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Size selectivity of codend mesh size of trawl for Decapterus maruadsi in northern part of South China Sea
LI Yanan, YANG Bingzhong, ZHANG Peng, LI Jie, WANG Teng, YAN Lei
 doi: 10.12131/20210256
[Abstract](171) [FullText HTML](40) [PDF 801KB](39)
To determine the suitability of minimum mesh size standards for trawls in the South China Sea, we conducted selectivity tests in that area by using the covered net method with mesh sizes of 30, 35, 40 and 45 mm (Denoted as D30, D35, D40 and D45, respectively). We used Logistic and Richards models to fit selectivity curves for Decapterus maruadsi by the maximum likelihood method, and determined the best-fitting curves by comparing the model deviations and degrees of freedom of the two models. The results show that the Logistic curve fitted better for D30, D35 and D45 mesh codend, while the Richards curve fit better for D40 mesh codend. The 50% retention fork lengths (L0.5) of D. maruadsi for D30, D35, D40 and D45 were 12.43, 12.88, 13.60 and 16.79 cm, respectively. As the mesh size increased, the L0.5 of D. maruadsi increased but the selection range decreased gradually. The minimum mesh size was 41.39 mm based on the relationship between L0.5 and mesh size of D. maruadsi. Thus, 45.39 mm is suggested as the minimum mesh size for trawl in the South China Sea to protect small and medium-sized economic fish such as D. maruadsi.
Relationship between body mass and activities of digestive enzymes and immune-related enzymes of juvenile yellowfin tuna (Thunnus albacares)
ZHOU Shengjie, YANG Rui, YU Gang, MA Zhenhua
 doi: 10.12131/20210191
[Abstract](39) [FullText HTML](4) [PDF 819KB](11)
In order to accumulate the land-based recirculating aquaculture basic data of juvenile yellowfin tuna (Thunnus albacares), we studied the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), amylase, lipase and protease in the serum, muscle tissue, liver, stomach, intestine and other tissues of the juveniles of different body mass. The ACP activity showed a descending order of intestine>muscle>liver>serum, while the AKP activity showed a descending order of intestine>liver>muscle>serum. With the increase of body mass, there was little difference in the ACP activity in muscle, intestine and liver, while the AKP activity in liver increased gradually, and there was significant difference between the two adjacent groups (P<0.05). In general, the digestive enzyme activity of the larvae was stable, without significant difference between the groups (P>0.05). Only when the body mass reached 1 000 g, the intestinal trypsin activity decreased significantly (P<0.05), and then floated in a small range, without significant difference between the groups (P<0.05). In conclusion, the ACP and AKP activities are high and stable in the tissues of juvenile T. albacares, which ensures stable functions for the decomposition, absorption and reuse of phosphorus (P) and immunity to external substances; during the breeding period of T. albacares, the nutritional demand is stable and the protein demand is strong.
Cumulative changes of off-flavor compounds of grass carp in two culture systems
YAN Li, LI Kang, KAMALA Gharti Chetri, LU Qiang, XU Yan, LIU Rucong, WANG Guixiang, ABDOUL Gadiri Sow, LIU Liping
 doi: 10.12131/20210167
[Abstract](244) [FullText HTML](41) [PDF 789KB](8)
In order to investigate the influence of culture systems on the accumulation of off-flavor substances in the aquaculture water and grass carp (Ctenopharyngodon idella), we studied the accumulation of geosmin (GSM) and 2-methylisoborneol (2-MIB) in the fish in the in-pond raceway system (IPRS) and the traditional culture system. We dynamicaclly detected the contents of the two compounds in the water and fish muscles in different culture systems and applied the Pearson analysis. The results show that the 2-MIB concentration in the water and fish muscle in the IPRS system increased significantly with the extension of aquaculture time. The GSM concentration also showed a gradual accumulation trend, and the changes in the concentrations of the two compounds in the muscle remained consistent with those in the water. In the traditional pond system, the concentration of 2-MIB gradually increased without significant difference, and the fish muscle had significantly higher concentration at the end of the experiment than at previous stages. The GSM concentration of both pond water and fish muscle first decreased and then increased. Correlation analysis shows that the accumulation of both GSM and 2-MIB was positively correlated with fish body mass and length. In conclusion, the accumulation of off-flavor compounds in pond water and fish muscle is affected by the culture system. Grass carp with body mass of 0.42–1.23 kg accumulates off-flavor compounds faster.
Effects of dietary Clostridium butyricum supplementation on growth performance and intestinal flora of juvenile Trachinotus ovatus
WU Yang, YANG Keng, HUANG Xiaolin, ZHOU Chuanpeng, XU Chuangwen, HUANG Zhong, YU Wei, XUN Pengwei, HUANG Jianbin, MAI Xiaoyong, LIN Heizhao
 doi: 10.12131/20210141
[Abstract](265) [FullText HTML](36) [PDF 942KB](14)
We evaluated the effects of dietary Clostridium butyricum supplementation on the growth performance and intestinal microbiota of juvenile Trachinotus ovatus, so as to provide a theoretical basis for the application of C. butyricum in T. ovatus aquaculture. In this study, five kinds of experimental feeds [0, 1% (1×107 CFU·g−1), 2% (2×107 CFU·g−1), 3% (3×107 CFU·g−1) and 4% (4×107 CFU·g−1) of C. butyricum] had been sprayed on the basic feed to feed T. ovatus for eight weeks. The results show that dietary supplementation of 2% C. butyricum improved the feed utilization rate of juvenile T. ovatus significantly. The diversity of intestinal flora was significantly different from that in control group and 4% supplemental group (P<0.05). The principal co-ordinates analysis and principal component analysis show that the added amount of C. butyricum in the feed was the main factor for the change in the structure of the intestinal flora of juvenile T. ovatus. At phylum and genus level, C. butyricum supplemental group and control group show difference at different degrees. Dietary supplementation with C. butyricum improved the growth performance and intestinal health of juvenile T. ovatus.
Algae-lysing characteristics of an algicidal bacterium G2 from reservoir sediment
YUAN Keting, REN Dajun, WAN Qiong, CHAI Beibei, KANG Aiqing, LEI Xiaohui, CHEN Bin, Chen Xiang
 doi: 10.12131/20210187
[Abstract](63) [FullText HTML](14) [PDF 1516KB](9)
Microcystis aeruginosa can cause algal blooms, which has been a serious threat to the water environment. Microbial algae removal is a technology with good application prospects. In this study, we isolated a new algae-dissolving bacterium G2 from the reservoir substrate of Xi'an of Shaanxi Province, identified as Cellvibrio sp. according to 16S rDNA sequence analysis (GenBank accession No.: MW221316), and investigated the feasibility of G2's solubilizing M. aeruginosa. Results show that G2 solubilized algae by secreting extracellular substances indirectly, and it had the best removal effect on algae during the stabilization period. Increasing G2 dosing ratio (>10%) contributed to the effect of algae dissolution. G2 was sensitive to the change of temperature, and the algae removal rate reached (59.42±0.88)% and (63.10±1.42)% at 5 and 25 ℃, respectively. The removal efficiency was poor at temperatures higher than 75 ℃. The pH and light had no significant influences on the algae removal effect, and G2 had strong tolerance to acid and alkali (pH 3−11). In conclusion, G2 can inhibit the growth of M. aeruginosa efficiently, so it is a promising biocontrol agent to mitigate cyanobacterial blooms.
Effects of inositol on growth and metabolism for juvenile Litopenaeus vannamei at different salinities
HE Guilun, YI Yuanming, YANG Qihui, TAN Beiping, CHI Shuyan, LIU Hongyu
 doi: 10.12131/20200186
[Abstract](179) [FullText HTML](37) [PDF 751KB](12)
To study the effects of inositol on the growth, serum biochemical indices, and non-specific immunity of juvenile Litopenaeus vannamei at different salinities (4 and 28), we fed the shrimps of the initial body mass of (0.75±0.00) g with six diets containing 0, 100, 200, 400, 800 and 1 600 mg∙kg−1 inositol for 10 weeks, respectively. The results show that the final body mass, weight gain rate, survival rate, specific growth rate, protein efficiency, net protein utilization, total cholesterol, acid phosphatase, alkaline phosphatase, total superoxide dismutase and nitric oxide synthase were significantly higher at high salinity than at low salinity (P<0.05); while the feed coefficient and moisture were the reverse. The feed coefficient and total cholesterol content decreased with increasing inositol levels in the diet, but the final body mass, weight gain rate, survival rate, specific growth rate, protein efficiency and net protein utilization increased, and the hepatopancreas somatic indices, acid phosphatase and alkaline phosphatase were significantly higher in inositol-added groups than in the control group (P<0.05). In summary, feeding inositol diets are recommended to improve shrimp's growth, survival and immutability; shrimp's growth and immunity are suppressed at low salinity; feeding higher than 100 mg∙kg−1 inositol diets can restore the growth to a high salinity level, and feeding higher than 200 mg∙kg−1 inositol diets can improve shrimp's immunity.
Effects of dietary alginate oligosaccharide on growth performance, antioxidative capacity and immune function of juvenile Trachinotus ovatus
HUANG Jianbin, CHI Yan, ZHOU Chuanpeng, HUANG Xiaolin, HUANG Zhong, YU Wei, XUN Pengwei, WU Yang, ZHANG Yu, LIN Heizhao
 doi: 10.12131/20210161
[Abstract](156) [FullText HTML](29) [PDF 1101KB](19)
Trachinotus ovatus juveniles (225 individuals) were fed for 58 d with three diets containing 0 (Control: TC), 0.7 (A1) and 6.0 g·kg−1 (A2) alginate oligosaccharide (AO) to investigate the effects of AO on the growth, plasma biochemical and immune indexes, hepatic antioxidative capacity, intestine morphology and expression of genes involved in Nf-κb signaling pathway of T. ovatus. The results show that the weight gain rate and specific growth rate of T. ovatus of both A1 and A2 group were significantly higher than those of TC group (P<0.05). The feed coefficient of A1 group was significantly lower than that of TC group (P<0.05). Compared with TC group, the mass concentration of plasma C3 increased in both A1 and A2 group significantly (P<0.05), and the activity of alkaline phosphatase increased in A2 group significantly (P<0.05). Compared with TC group, the activities of SOD, CAT, POD and GR and T-AOC increased in both A1 and A2 significantly, while the concentration of MDA decreased significantly (P<0.05). The height of villus in A1 and A2 group were significantly higher than those of TC group (P<0.05). Compared with TC group, the expressions of ikk, nf-κb, tnf-α and il-8 decreased in A1 and A2 group significantly, while the expressions of tgf-β increased significantly (P<0.05). In conclusion, AO supplementation in diet can improve the growth and intestine morphology of T. ovatus, enhance the plasma immune indexes and hepatic antioxidative capacity, inhibit the expression of intestinal Nf-κb and proinflammatory cytokine mRNA, and improve the expression of antiinflammatory cytokine mRNA. The suitable level of AO in diet is 0.7 g·kg−1.
Comparison of reproductive performance, embryo color and biochemical composition of white and green carapace strains of Chinese mitten crab (Eriocheir sinensis)
ZHANG Dongdong, FAN Chenwei, JIANG Xiaodong, CHEN Yu, WU Xugan
 doi: 10.12131/20210268
[Abstract](87) [FullText HTML](17) [PDF 841KB](12)
To investigate the reproductive performance of a new white carapace strain of Chinese mitten crab (Eriocheir sinensis), we compared the breeding experiments and gastral embryo quality of white and green carapace strains in indoor tanks. The results show that the ovigerous rate, survival rate and spawning rate of the white carapace strain were higher than those of the green carapace strain, but the egg production, fecundity and reproductive effort of the white carapace strain were slightly lower than those of the green strain. There were no significant differences in the egg diameter, wet and dry mass of single egg between the two strains (P>0.05). In addition, no significant differences were found in the color parameters in dried eggs (P<0.05) and the contents of total carotenoids, zeaxanthin, canthaxanthin and β-carotene in both strains were similar (P>0.05), but the contents of astaxanthin and lutein in dried eggs in the white carapace strain were significantly lower than those in the green carapace strain (P<0.05). Besides, the eggs of both strains had similar moisture, total lipid and crude protein contents (P>0.05). As for fatty acid composition of eggs, the percentage of C18:1 n-9 in the white carapace strain was significantly higher than that in the green carapace strain (P<0.05), but there were no significant differences in other fatty acid contents (P>0.05). In conclusion, the female ovigerous rate of the white carapace strain is faster than that of the green carapace strain, but the reproductive performance, eggs color and proximate composition are similar.
Effect of salinity on growth of planktonic larvae of sea cucumber (Holothuria leucospilota)
HUANG Xingmei, ZHAO Wang, LI Changlin, DENG Zhenghua, ZHANG Yuwei, WEN Weigeng, MA Zhenhua, YU Gang
 doi: 10.12131/20210100
[Abstract](58) [FullText HTML](15) [PDF 1212KB](5)
In order to improve the survival rate of larval breeding of Holothuria leucospilota and provide a theoretical basis for the development and utilization of wild resources of tropical sea cucumber, we investigated the effects of salinity on the growth, development and survival rate of planktonic larvae of H. leucospilota by measuring the growth and development of the planktonic larvae under different salinity conditions and analyzing the effects of body length, stomach width and survival rate of the planktonic larvae on its growth. Results demonstrate that the specific growth rates (SGR) of body length in the salinity groups of 33 and 36 were significantly higher than those in the other salinity groups (P<0.05), and there was no significant difference between the salinity group of 24 and 27, 33 and 36 (P>0.05). When the salinity was 30, the SGR of larval stomach width was significantly higher than that in the other salinity groups (24, 33 and 36 salinity groups, P<0.05). When the salinity was 27−30, the development and survival rate of stomach of planktonic larvae were the best, and its overall shape was stronger and clearer. Therefore, 27−30 is the optimal salnility for the development of plankton larvae of H. leucospilota.
Protective effects of addition of nano cerium oxide in diets on Eriocheir sinensis under ammonia-nitrogen and Aeromonas hydrophila stresses
SUN Yuanchen, XU Bingjie, CAO Yichou, XU Yingjie, QIN Fenju, YUAN Hongxia
 doi: 10.12131/20210209
[Abstract](131) [FullText HTML](50) [PDF 804KB](25)
To explore the mechanism of Chinese mitten crabs (Eriocheir sinensis) dealing with adverse water environmental stresses, we studied the effects of nano cerium oxide (nCeO2) on the immunity and antioxidant capacity of the crabs under ammonia-nitrogen and Aeromonas hydrophila stresses. The crabs were continuously fed with diets supplemented with different doses of nCeO2 (0, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8 mg·kg−1) for 90 d, then the ammonia-nitrogen and A. hydrophila stress tests were conducted. The results show that: 1) Both the single ammonia-nitrogen stress and dual stresses of ammonia-nitrogen and A. hydrophila (henceforth called "dual stress") decreased the survival rates of the crabs significantly (P<0.01); the activities of acid phosphatase (ACP), alkaline phosphatase (AKP) and lysosome (LZM) increased (P<0.01 or P<0.05); the activities of superoxide dismutase (SOD) and catalase (CAT) decreased significantly (P<0.01), while the concentration of malondialdehyde (MDA) increased (P<0.01 or P<0.05); 2) Suitable nCeO2 dose could enhance the survival rates of crabs under the single ammonia-nitrogen stress and dual stress (P<0.01 or P<0.05), increase the activities of SOD and CAT significantly (P<0.01), decrease the concentration of MDA (P<0.01 or P<0.05), further increase the activity of LZM (P<0.01), but the activities of ACP and AKP only increased under dual stress (P<0.01). Above all, suitable supplementation of nCeO2 can ameliorate the decline of survival rates and antioxidant capacity of E. sinensis under the the single ammonia-nitrogen stress and dual stress, and increase the immunity enzyme activities. The suitable nCeO2 supplementation doses for protecting crabs are 0.8 and 1.6 mg·kg−1 under single and dual stress, respectively.
Differential analysis of microRNAs in zebrafish gills under hypoxic stress
LIN Feng, JIA Ruonan, WANG Faxiang, XU Qianghua
 doi: 10.12131/20210124
[Abstract](139) [FullText HTML](36) [PDF 2326KB](5)
In order to study the biological function of microRNAs (miRNAs) in response to hypoxic stress, we perfomed high-throughput miRNAs sequencing in the gill tissues of zebrafish (Danio rerio) under hypoxic stress and normoxic condition, and analyzed the differences in miRNAs expression in the gill tissues of zebrafish. The results show that a total of 15 miRNAs are significantly differentially expressed in the gills of zebrafish under hypoxic stress and normoxic condition, among which 13 miRNAs were up-regulated significantly and 2 miRNAs were down-regulated significantly. Moreover, we performed a correlation analysis on miRNAs sequencing and zebrafish gill transcriptome, and predicted the target genes for 28 heat shock protein genes that were significantly differentially expressed under hypoxic stress and normoxic condition screened in the previous stage. The result shows that miR-455-3p, which was expressed significantly low under hypoxic stress, targeted to increase the expression of hspa14 and dnajb6b and enhance the adaptability to hypoxic stress. In addition, miR-194a and miR-155, which were highly expressed under hypoxic stress, targeted five heat shock protein genes (hspa12a, dnajc5aa, hspb7, hsp70.3, dnajb2) and four heat shock protein genes (hspa12a, hspg2, hspa13, dnajb2) to regulate zebrafish's adaptation to hypoxic condition.
Characterization and expression analysis of PP2C from Penaeus monodon under acute low salt and ammonia nitrogen stress
SI Mengru, LI Yundong, YANG Qibin, JIANG Song, YANG Lishi, HUANG Jianhua, JIANG Shigui, ZHOU Falin
 doi: 10.12131/20210193
[Abstract](162) [FullText HTML](26) [PDF 1191KB](6)
Protein phosphatase 2C family protein is a class of protein phosphatases that plays an important role in stress resistance. However, there are few studies in crustaceans. In this study, we cloned and obtained the full-length cDNA of protein phosphatase 2C (PmPP2C) with c-type domain in Penaeus monodon by rapid amplification of cDNA ends (RACE). The full length of ORF was 2 079 bp, encoding 692 amino acids. The real-time fluorescence quantitative results show that PmPP2C was expressed in all the tested tissues. The expression was the highest in hepatopancreas and gill tissues, followed by thoracic nerve, testis and muscle. The expression of PmPP2C in hepatopancreas and gill was first down-regulated and then up-regulated under 96 h acute low salt stress. The expression of PmPP2C in hepatopancreas and gill showed a downward-upward-downward trend under 96 h acute ammonia nitrogen stress. The results indicate that PmPP2C can be involved in the response of P. monodon to acute low salt and ammonia nitrogen stress, suggesting that it may play an important role in the immune defense against environmental stress.
Metabonomics analysis of ovaries of Coilia nasus in seawater and freshwater based on liquid chromatography-mass spectrometry
GAO Shufang, ZHANG Jinpeng, SHI Yonghai, YUAN Xincheng, LIU Qigen
 doi: 10.12131/20210185
[Abstract](178) [FullText HTML](83) [PDF 1088KB](50)
In order to clarify the effects of seawater and freshwater on the ovary development of Coilia nasus, we analyzed their differences by using non-targeted metabolomics, and compared with database of KEGG directly to find out the corresponding metabolic pathways, then analyzed its causes. The results show that a total of 47 metabolites had significant difference between the two groups (P<0.05, FC>1, VIP>1). Compared with the seawater group, the most significant differences in the expression were carbocyclic thromboxane A2, Galactosylceramide, and their differences were 10.40 and 2.78 times, respectively. The cortisol in the ovarian tissue of the freshwater group increased by 1.61 times. According to the analysis on KEGG metabolic pathways of 47 different metabolites, the biosynthesis of aminoacyl-tRNA and pyridine metabolic pathways changed in the seawater and freshwater environments significantly (P<0.05). The biosynthesis pathway of cortisol, aminoyl-tRNA, pyrimidine metabolism pathway and sphingo-lipid metabolism pathway may be related to the ovarian development during the reproductive migration of C. nasus.
Sequencing of whole genome of Bacillus velezensis LG37 and screening of inorganic nitrogen metabolism candidate genes
LIU Guangxin, DONG Yanjun, ZHAO Lijuan, DENG Yiqin, CHENG Changhong, MA Hongling, JIANG Jianjun, FENG Juan, GUO Zhixun, LIN Li
 doi: 10.12131/20210149
[Abstract](190) [FullText HTML](27) [PDF 1620KB](8)
It has been found that Bacillus velezensis can assimilate inorganic nitrogen efficiently. However, the underlying mechanism of inorganic nitrogen assimilation remains enigmatic. In order to elucidate the mechanism, we sequenced the complete genome of LG37 by PacBio RS II and Illumina HiSeq 2000, and then annotated and analyzed the sequence by the database of NR, KEGG, eggNOG, GO and CARD. Finally, we screened the genes related to inorganic nitrogen metabolism by local Blast+. The results show that: 1) The genome contained one circular chromosomal with a size of 3 929 697 bp and a GC-content of 46.5%. Gene prediction and annotation was performed to acquire a total of 3 854 protein-coding genes, 86 tRNA genes and 27 rRNA genes. 2) A total of 94 inorganic nitrogen metabolism candidate genes were screened by local Blast+. These genes were involved into coding sensing protein, transcriptional regulator, transporter, oxidoreductase and assimilator, etc.. In conclusion, the whole genome sequencing and data analysis of LG37 provide data at gene level and theoretical basis for functional study and application of Bacillus in reducing inorganic nitrogen in aquaculture water.
Spatial distribution and density changes of fish resources in East Dongting Lake during early fishing ban period
JIA Chunyan, WANG Ke, LI Huifeng, GAO Lei, YANG Hao, LIU Shaoping, CHEN Daqing, DUAN Xinbin
 doi: 10.12131/20210148
[Abstract](161) [FullText HTML](25) [PDF 1132KB](11)
In order to find out the density distribution of fish resources in the East Dongting Lake during the early fishing ban period, and provide data support for the effect evaluation of the fishing ban and the protection of fishery resources, we conducted the hydroacoustic surveys in the central area of the East Dongting Lake and the Xiangjiang floodway from November 2 to 8, 2020. The results show that the average target strength of fish in the survey area was −46.48 dB; the average body length was about 18.66 cm, and the body length ranged from 1.63 to 113.50 cm. The difference of fish target intensity between the different regions was significant. The average fish density in all the survey segments was 150.20 ind.· (1 000 m3)−1, ranging from 14.47 to 1 823.95 ind.· (1 000 m3)−1. The average fish density in the East Dongting Lake was greater than that in the Xiangjiang floodway, and there were significant differences in the average density of fish among different regions (P<0.05), highest at the confluence of rivers and lakes. Compared with the survey data of the East Dongting Lake before the fishing ban (2015), the average target intensity of fish after the fishing ban decreased, while the average density of fish increased significantly (P<0.05).
Spatial pattern of fish taxonomic diversity along coastal waters in northern South China Sea
MAI Guangming, CHEN Zhijie, WANG Xuefeng, XIAO Yayuan, LI Chunhou
 doi: 10.12131/20210117
[Abstract](159) [FullText HTML](45) [PDF 1162KB](10)
Fish taxonomic diversity is the basis of fish diversity protection and community stability analysis. Based on the monitoring and historical data of fishery resources in seven coastal waters of the northern South China Sea (Leizhou Bay, Daya Bay, Pearl River Estuary, Lingshui Bay, Hailing Bay, Fangchenggang and Nan'ao Island) during 2014 to 2017, we analyzed the species composition and spatial pattern of fish taxonomic diversity by studying the taxonomic diversity index and taxonomic dissimilarity index, in addtion with a cluster analysis. The results show that: 1) A total of 1 105 fish species had been identified. The species richness was the greatest in the Pearl River Estuary (958 species) and the least in Nan'ao Island (94 species). 2) The seven waters can be divided into two groups: Group I (Leizhou Bay, Pearl River Estuary and Daya Bay) had high taxonomic diversity and uneven genetic relationship; Group II (Lingshui Bay, Nan'ao Island, Hailing Bay and Fangchenggang) had low taxonomic diversity. 3) The variation range of average taxonomic distinctness index (∆+) in each water was small (54.3–61.04), and the variation of Δ+ was not positive with the increase of latitude. 4) The ∆+ of Lingshui Bay, Hailing Bay and Fangchenggang fell in the outside of the 95% confidence funnel. In conclusion, the tropical-subtropical characteristics of fish species in the surveyed area are generally obvious, with a decreasing trend of ∆+ of Bohai Sea>Yellow Sea>East China Sea>South China Sea; Lingshui Bay, Hailing Bay and Fangchenggang might have habitat degradation, which indicates that the research on fishery monitoring is necessary for the fishes biodiversity protection.
Establishment and optimization of environmental DNA extraction method from water of Pearl River Estuary
LI Hongting, ZHANG Shuai, ZOU Keshu, CHEN Zuozhi, CHEN Xiaolei, JIANG Peiwen, CAO Yiting, LI Min
 doi: 10.12131/20210304
[Abstract](148) [FullText HTML](38) [PDF 1346KB](22)
Environmental DNA (eDNA) technology has been widely used in the study of aquatic biodiversity in recent years. In this study, different filter membrane, storage method of membrane and DNA extract kits were used to evaluate effectiveness of eDNA enrichment from the brackish water in the Pearl River Estuary. Four kinds of filter membranes with diameter of 47 mm and pore size of 0.45 μm (Nitrocellulose membrane, cellulose acetate membrane, glass fiber membrane and polycarbonate membrane) were selected. Four kinds of membrane preservation methods were adopted and two kinds of DNA extract kits were used. The results show that filter membrane materials and preservation methods had a significant impact on the yield of eDNA. The highest concentration of eDNA was obtained by cellulose acetate membrane. Under the condition of the same quality of DNA yield, the concentration of eDNA extracted by Marine Animal Tissue Genomic DNA Kit was higher than that by DNeasy Blood and Tissue Kit. The concentration of eDNA obtained from ‘liquid nitrogen’ storage method was the highest among the four storage conditions. However, the concentration of eDNA was acceptable for alcohol preserved method at room temperature when cryopreservation was not available. Filtering water samples immediately after sampling can prevent eDNA degradation effectively. This study established a systematic protocol for eDNA extraction of water samples from the brackish ecosystem in the Pearl River Estuary, providing references for eDNA research in similar waters.
Preliminary metabacording dietary analysis of Diaphus splendidus in South China Sea
CHEN Xiaolei, LI Min, CHEN Zuozhi, ZHANG Jun, ZHANG Shuai, QI Zhanhui, XU Shannan
 doi: 10.12131/20210199
[Abstract](224) [FullText HTML](39) [PDF 699KB](10)
Dietary analysis of fish is an important part of fish biology and ecology as well as the basis of fishery resources development. In this study, the gastric DNA of Diaphus splendidus was extracted, and the mitochondrial cytochrome c oxidase subunit I (COI) was amplified as a molecular marker. The food composition was identified by high-throughput sequencing. The results show that a total of 34 species belonged to 5 phyla, 7 classes, 11 orders, 18 families and 29 genera. The diet of D. Splendidus mainly included Ostracoda, Copepoda, Amphipoda, Fish, Jellyfish, Euphausiacea, Gastropod and Polychaeta. Ostracoda, Copepoda and Amphipoda were the dominant groups in its food composition, which is basically consistent with the previous research based on traditional morphological identification, except for jellyfish that was identified only by this study. In conclusion, DNA metabarcoding method is suitable for the food analysis of D. splendidus in the South China Sea, and has higher identification potential than the food analysis based on morphology.
Preliminary construction and comparative analysis of environmental DNA metabarcoding reference database of freshwater fishes in Hainan Island
CHEN Zhi, CAI Xingwei, ZHANG Qingfeng, LI Gaojun, MA Chunlai, SHEN Zhixin
 doi: 10.12131/20210339
[Abstract](133) [FullText HTML](20) [PDF 1298KB](14)
In order to determine the optimal reference database and target genes for environmental DNA study of freshwater fishes in Hainan Island, we compared the species coverage, annotation accuracy and threshold values of interspecific difference of COI, 12S and 16S between the self-built database and the public database. The results show that: 1) Seventy-two fish species were collected, among which 16 (COI), 20 (12S) and 22 (16S) species' reference sequences were provided for the first time. 2) Only 68.06% (COI), 66.67% (12S) and 69.44% (16S) of the fish had high similarity sequence in the public database. 3) The annotation accuracy based on the self-built database was significantly higher than that on the public database (COI: 100% vs 69.64%; 12S: 96.15% vs 67.30%; 16S: 96% vs 70%). 4) COI gene was the best target gene for identifying freshwater fishes in Hainan Island, followed by 16S gene. 5) The threshold values of interspecific difference based on K2P genetic distance were 0.006 9 (COI), 0.005 6 (12S) and 0.007 5 (16S), respectively, and the accuracy rates were 94.96% (COI), 89.05% (12S) and 92.70% (16S), respectively. This study reveals that the sequence annotation accuracy of the self-built database is significantly higher than that of the public database, and it is suggested that COI and 16S should be used as the environmental DNA metabarcoding genes of freshwater fishes in Hainan Island.
Construction of DNA meta-barcode database of fish in Pearl River Estuary based on mitochondrial cytochrome COI and 12S rDNA gene
JIANG Peiwen, LI Min, ZHANG Shuai, CHEN Zuozhi, XU Shannan
 doi: 10.12131/20210210
[Abstract](269) [FullText HTML](48) [PDF 3461KB](16)
In order to establish a DNA barcode background database of fish in the Pearl River Estuary and provide information basis for fish species identification and diversity research, we had collected 251 samples from the Pearl River Estuary from 2020 to 2021, and determined 652 bp fragments of mitochondrial cytochrome oxidase subunit I (COI) of 219 individuals and 163−185 bp fragments of mitochondrial 12s rDNA of 247 individuals of 99 species, 10 families, 41 genera, 6 orders. Besides, we downloaded 165 COI sequences and 128 12S rDNA sequences from GenBank database, and had obtained 384 COI sequences and 375 12S rDNA sequences of 172 species of fish. The results show that the average intraspecific genetic distance of COI sequence was 0.20%, and the average interspecific genetic distance was 25.54%. The average intraspecific genetic distance of 12S rDNA sequence was 0.12%, and the average interspecific genetic distance was 34.39%. The DNA barcode of COI gene could form an obvious barcode gap, but the DNA barcode based on 12s rDNA gene could not, and it was difficult to distinguish the 11 species (6.4% of the total species). The establishment of the DNA barcode database of fish in the Pearl River Estuary is conductive to the environmental DNA analysis of the fish ecosystem in that area, providing reliable technical support for the protection of fish biodiversity and the monitoring of population dynamics in the Pearl River Estuary.
Identification of a novel oyster-related circovirus genome compa-rative genome analysis of oyster-related circoviruses
YANG Liling, GUO Yingxiang, WEI Hongying, WANG Meng, FANG Yifei, ZHU Peng, JIANG Jingzhe
 doi: 10.12131/20210260
[Abstract](161) [FullText HTML](14) [PDF 1405KB](5)
The lack of pathogen genome information is one of the main reasons for the slow progress of oyster disease research. In order to identify more oyster-associated viruses, based on the previously obtained viromic data of oysters (Crassostrea hongkongensis) cultured in multiple locations along the coast of the South China Sea, after quality control, assembly, and species annotation of the sequencing data, we selected the putative circovirus genome sequences for the construction of the phylogenetic tree, genome comparison, protein domain analysis, structure prediction and virus abundance analysis, which provides references for the research of oyster disease. The results show that five viral sequences clustered with known circoviruses in a large branch, indicating that they are members of the Circoviridae family. The five viral genome sequences all contained replication protein genes, with the highest similarity to a replication protein sequence of arthropod circovirus. The five sequences and seven other public database sequences formed an independent sub-branch. Viruses on this branch were mostly from animal-related samples. Based on the domain analysis (SMART), replicase conserved domains were identified in most sequences.
Relative energy accumulation in soma and gonad tissues of female Dosidicus gigas and relation to environmental effects
LIAN Jinxin, FENG Yixuan, LIN Dongming
 doi: 10.12131/20210219
[Abstract](134) [FullText HTML](36) [PDF 1399KB](5)
In order to understand the life history strategy of Dosidicus gigas in terms of energy accumulation, we applied the methodology tissue energy density technique and generalized linear mixed-effects models (GLMM) to investigate the relative energy accumulation in soma and gonad tissues. The specimens of D. gigas were collected from the commercial jigging fisheries during 2017 and 2019. The results show that soma tissue was the largest organ for energy accumulation, accounting for at least 70% of the total energy of D. gigas, while gonad tissues accumulated a small portion of energy. The relative energy accumulation in soma tissue declined significantly from physiologically maturing stage to functionally mature stage, followed by a significant rebound at the spawning stage. In contrast, the relative energy accumulation in gonad tissues showed an increasing trend after the onset of physiologically maturing, reaching a peak at the stage of functionally mature. The relative energy accumulation in soma was not significantly correlated with sea surface temperature, neither was the relative energy accumulation in gonad tissues. However, there was significant relationship between the relative energy accumulation in both soma and gonad tissues and sea surface chlorophyll-a concentration. There was also significant relationship between the relative energy accumulation in soma and gonad tissues and sampling longitudes in the East Pacific Ocean. These observations indicate that D. gigas increases energy allocation to gonadal development after the onset of physiologically maturing, and maintains somatic condition during the spawning period. The relative energy accumulation in soma and gonad tissues may be more likely related to marine production, due to larger relative energy accumulation associated with higher chlorophyll-a concentration.
Optimization of thermal sterilization process for low-acid and acidified instant laver
GE Mengmeng, SHEN Jiandong, TANG Xiaohang, XIA Wenshui, XU Yanshun
 doi: 10.12131/20220003
[Abstract](46) [FullText HTML](11) [PDF 1018KB](5)
In order to optimize the sterilization process of laver (Porphyra spp.) and develop high-quality instant wet laver products, we measured the heat penetration curves during high-pressure heat treatment (110, 115, 121 ℃) and normal pressure heat treatment (85, 90, 95 ℃) for low-acid and acidified lavers (pH≤4.6). Combined with preservation experiment and microbial analysis, we determined the F-value (safe sterilization heating time) corresponding to the two sterilization methods, and explored the effects of different temperature-time combinations on the sensory and nutritional quality of laver with the same F-value. Results show that low-acid laver could reach commercial sterility when F0 was 3 min under high-pressure heat sterilization, and acidified laver could also reach the preservation requirements when \begin{document}$ {F\,}_{93.3}^{8.89} $\end{document} was 5 min under normal pressure heat sterilization. Compared with high-pressure heat sterilization, acidification combined with normal pressure sterilization could obtain better texture and color. The toughness, hardness and sensory score of laver increased with the increase of sterilization temperature with the same F-value. In terms of nutrients, the total soluble sugar and free amino acids decreased with the increase of temperature in the high-pressure group. The highest free amino acids content was obtained at 90 °C in the normal-pressure group. In general, the texture, sensory and nutritional quality were better when the sterilization parameters were 90 °C, 11.5 min (acidified group) and 115 °C, 8 min (low-acid group).
Effects of different C/N ratios on formation of biofloc, water quality and microflora in aquaculture water of Chinemys reevesii
ZHANG Kai, LIN Yijing, LI Chenyang, LIU Fangling, SHEN Minghao, ZHENG Shanjian
 doi: 10.12131/20200144
[Abstract](112) [FullText HTML](39) [PDF 1032KB](6)
In order to determine the feasibility and the best addition amount of biofloc technology in turtle culture, we studied the formation of biofloc and its effects on water quality and microflora by regulating the C/N ratio in the culture water of Chinemy sreevesii. We carried out the experiment with the addition of sucrose at 10∶1, 15∶1, 20∶1 and the control group for 40 d. The results show that the biofloc volume index of each group of biofloc became stable after 28 d, and the treatment effect of ammonia nitrogen and nitrite was significant when the C/N ratio≥10∶1. Among them, the removal rate of ammonia nitrogen and nitrite after 40 d of the group with a C/N ratio of 15∶1 were 76.7% and 64.4%, respectively, which indicates that the C/N ratio of 15∶1 can promote the formation of biofloc, and reduce the level of ammonia nitrogen and nitrite in the water effectively. The biological flocs of the experimental group (C/N=15∶1) and the control group were sequenced by high-throughput sequencing, and the results show that the dominant phyla of biofloc in the two water bodies were Proteobacteria, Bacteroidetes and Actinobacteria, but the proportion of each dominant bacteria phylum was different. In conclusion, the addition of different C/N ratios can affect the formation of biofloc, water quality and microflora of C.reevesii ponds. 15∶1 is the optimal C/N ratio for the formation of biofloc, which can promote the formation of biofloc and has a strong ability to regulate water quality.
Mathematical analysis of morphometric attributes effects on body mass for four-month-old Plectropomus leopardus
YU Wei, LIN Heizhao, MA Zhenhua, WU Qia'er, CHEN Xueqing, YANG Yukai, HUANG Xiaolin, HUANG Zhong, ZHAO Wang, LI Tao, ZHOU Chuanpeng
 doi: 10.12131/20210253
[Abstract](156) [FullText HTML](32) [PDF 605KB](6)
In this study, we selected 159 individuals of the same batch of 4-month-old coral trout (Plectropomus leopardus) juveniles as the experimental objects to explore the correlation between the eleven morphological traits and body mass. The results show that there were significnat correlation between snout length (x9) and body mass (P<0.05), and extremely significant correlation between the other ten morphological traits and body mass. The results of path analysis reveals that the standard length (x2), body depth (x4), body width (x5), head height (x7), snout length (x9) were the main decisive morphological traits on body mass. The direct effect coefficient of body depth on body mass was 0.444, indicating that body depth mainly affected body mass through direct action. However, the other morphological traits mainly affected body mass indirectly via body depth. The total decision coefficient of five morphological traits on body mass was 0.853, indicating that these morphological traits were the main factors affecting body mass. After eliminating the morphological traits with insignificant coefficient to body mass, we established the multiple regression equation by multiple regression analysis. The morphological traits retained by the multiple regression analysis were consistent with the results of path analysis.
Recognition of Acetes chinensis fishing vessel based on 3-2D integration model behavior
ZHANG Jiaze, ZHANG Shengmao, WANG Shuxian, YANG Yuhao, DAI Yang, XIONG Ying
 doi: 10.12131/20210263
[Abstract](240) [FullText HTML](53) [PDF 1436KB](14)
Since the yield of Acetes chinensis has decreased sharply year by year, China has begun to implement quota fishing measures for A. chinensis in offshore waters by using video surveillance technology to assist the fishing management. This paper proposes a method for identifying the behavior of A. chinensis fishing vessels based on the 3-2D fusion model, so as to provide a new solution for quota fishing management. By installing high-definition camera equipment at four fixed positions on the A. chinensis fishing vessel and recording the entire process of fishing operations, we had obtained more than 600 video surveillance data had been as initial data. Secondly, we filtered effective video data from the initial data, and divided and labeled them with five behaviors. In order to improve the efficiency of network training, we preprocessed the video data such as compression and frame number segmentation. Finally, the model was trained by building a 3-2D fusion convolutional neural network to realize the extraction and classification of fishing vessel behavior characteristics. The results show that the classification accuracy of the fishing vessel behavior recognition method was 95.35%; the recall rate was 94.50%; the average accuracy was 96.60%; the overall score of the model could reach 93.32%; and the average detection time was 35.46 ms·frame−1. The method can be used for real-time analysis of the fishing video of A. chinensis fishing boats.
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Special Issue: New Technology and Product Development of High-Quality Biological Processing of Aquatic Products

Cover & Content
2022, 18(2).  
[Abstract](30) [PDF 2495KB](13)
Research Paper
Bioinformatics analysis and efficient preparation of β-agarase from marine bacteria
YOU Yuxian, XIE Wenyan, BAN Xiaofeng, KONG Haocun, LI Caiming, LI Zhaofeng
2022, 18(2): 1-12.   doi: 10.12131/20210330
[Abstract](84) [FullText HTML](44) [PDF 5988KB](16)
In order to expand the high-quality agarase categories, make full use of seaweed resources, and realize the efficient preparation of functional agar oligosaccharides, we derived a β-agarase from the marine bacterium (Agarivorans gilvus WH0801)(β-AGAase) by using genome mining technology, and predicted its physical and chemical properties as well as structural characteristics by bioinformatics analysis. Based on the results, β-AGAase is a non-secreted protein. The β-AGAase was extracellular expressed in Escherichia coli through the introduction of signal peptides by molecular biology methods, and its production efficiency was significantly enhanced through fermentation regulation strategy optimization. The optimal fermentation conditions are as followed: seed culture medium with an inoculation time of 5 h; fermentation starting medium was TB (pH 7.0); carbon source was 6 g·L−1 of fructose; nitrogen source was 30 g·L−1 of yeast extract II. After being cultured at 25 ℃ for 2 h, IPTG was added with a final concentration of 0.025 mmol·L−1 for 48 h induction. Under these conditions, the obtained enzyme activity was 16.72 U·mL−1 and was about 5 times higher than the initial enzyme activity, which proves that β-AGAase is of great potential for industrial application.
Preparation and characteristic research of immobilized patatin lipase suitable for fish oil processing
TU Lanlan, XU Jingshen, CHEN Runsha, WU Jinhong, LI Xianghong, ZHANG Yong
2022, 18(2): 13-22.   doi: 10.12131/20210291
[Abstract](93) [FullText HTML](28) [PDF 25054KB](9)
Patatin, an ester hydrolase with lipase catalytic activity, can be applied to the hydrolysis of fat. To solve the problems of poor stability of free patatin lipase and difficult reuse in industrial production, we immobilized patatin lipase by coupled nano (ConA) magnetic beads to improve its catalytic characteristics of its industrial application. The results show that the average adsorption rate of ConA magnetic beads was 24.50%, and PAA-Fe3O4 was determined as the most suitable immobilization material. The optimal immobilization conditions are as follows: immobilization time of 47.2 min, immobilization temperature of 25.3 ℃, magnetic bead addition of 3.0 mg·mL−1. Immobilized patain had the highest hydrolytic substrate activity at 40.0 ℃ and pH 7.0. Compared with free patatin lipase, its temperature tolerance increased by about 123% and the pH tolerance increased by about 47%. After five consecutive reactions, 56.60% patatin activity was still retained, indicating that the immobilized nano magnetic beads improved the enzymatic catalytic characteristics of patatin, which provides a new enzyme system with stronger catalytic performance for its application in the processing of aquatic products such as oil fish.
Enzymatic synthesis and purification of Vitamin A docosahexaenoate
GAO Kunpeng, SUN Jian'an, MAO Xiangzhao
2022, 18(2): 23-30.   doi: 10.12131/20210288
[Abstract](113) [FullText HTML](28) [PDF 773KB](8)
Vitamin A shows a variety of physiological activities, such as maintaining normal vision, improving skin and anti-aging activity. However, it is extremely unstable and easily decomposed under the action of light, heat and oxygen. In this study, Novozyme435 was used to catalyze the transesterification reaction of Vitamin A acetate (VAAE) and ethyl docosahexaenoate (EDHE). The target product (Vitamin A docosahexaenoate, VADHE) was identified by high performance liquid chromatography (HPLC) and mass spectrometry (MS). On this basis, VADHE in the reaction system was purified by silica gel column chromatography (C18 filler). The result of HPLC shows that the purity of VADHE reached 90%. In order to increase the yield of VADHE, the transesterification reaction was optimized in organic solvent system and solvent-free system, respectively. In the organic solvent system, the conversion rate reached 40.61% after 6 h. In the solvent-free system, when 100 mg Novozyme was used to catalyze the reaction for 4 h, the conversion rate reached 56.39%. VADHE was firstly designed and synthesized in this study, and the purified VADHE can be further used in the physiological activity experiment.
Heterologous expression of lipase Sv-lip5 and its application in hydrolysis of astaxanthin ester
YAN Jiao, GAO Kunpeng, YU Kexin, SUN Jianan, MAO Xiangzhao
2022, 18(2): 31-38.   doi: 10.12131/20210293
[Abstract](117) [FullText HTML](55) [PDF 1074KB](16)
Astaxanthin has a variety of physiological activities, but its most common form in nature is astaxanthin ester bound with different fatty acids. Hydrolysis of astaxanthin ester into free astaxanthin is an important research direction to improve the absorption and utilization of astaxanthin ester and to prepare astaxanthin ester with specific configuration. In this study, we heterologously expressed Sv-lip5 derived from Streptomyces violascens ATCC 27968 in Bacillus subtilis to explore the enzymatic properties and its application in astaxanthin ester hydrolysis. The results show that the optimal temperature of Sv-lip5 was 45 ℃; the optimal pH was 10.0 (Gly-NaOH buffer); and the enzyme activity of Sv-lip5 was higher than 55.7% after incubation at 35−55 ℃ for 21 h. As an alkaline resistant enzyme, the relative enzyme activity of Sv-lip5 could remain over 70% after incubation for 48 h under alkaline conditions. Sv-lip5 could hydrolyze astaxanthin ester in Haematococcus pluvialis oil effectively. Using p-nitrophenol palmitate as substrate, the specific activity of Sv-lip5 was 12.46 U·g−1. The optimal hydrolysis conditions of astaxanthin ester were: pH of 8.0, ratio of ethanol to buffer of 1:12; and the optimal enzyme dosage and time were 900 mg and 12 h, respectively. After adding 900 mg enzyme powder to 5.5 mL reaction system, the hydrolysis effect was obvious in 1 h, and the highest hydrolysis rate was 98.27% at 12th hour. The yield of astaxanthin in 200 μg astaxanthin ester was 147.48 μg. This method is high-efficiency for the biological hydrolysis preparation of free astaxanthin.
Recombinant expression of Bacillus licheniformis chitinase in B. subtilis and preparation of amino-oligosaccharides
YUAN Yuan, SU Lingqia, ZHANG Kang, ZHU Xuyang, XIA Wei, WU Jing
2022, 18(2): 39-47.   doi: 10.12131/20210297
[Abstract](92) [FullText HTML](46) [PDF 1038KB](6)
In this study, a chitinase blchiA from Bacillus licheniformis was recombinantly expressed in B. subtilis, and the B. subtilis engineering strain (B. subtilis WS9/pHY300PLK-blchiA) was constructed. The enzyme activity in the fermentation supernatant was 0.73 U·mL−1. The enzymatic properties of recombinant enzyme BLCHIA were characterized, and its best activity was obtained at pH 6.0 and 60 ℃, and the specific activity was 3.68 U·mg−1. 10 mmol·L−1 Cu2+ and Fe2+ could promote its activity, and its stability was good at pH 5.0−8.0 and 50−60 ℃. In addition, the catalytic ability of the recombinant enzyme on chitosan with a degree of deacetylation> 95% was significantly better than that of colloidal chitin, and the types of hydrocolloid chitin and chitosan were significantly different. Using colloidal chitin as substrate, the recombinant enzyme could mainly produce chitobiose, but using chitosan as substrate, it could produce chitosan oligosaccharide with polymerization degree of 2−7. The results have a good application prospect for viscosity reduction of chitosan and preparation of oligosaccharides with different polymerization degrees.
Identification of key amino acid sites for pH stability of GH46 family chitosanase
CHENG Yimeng, SUN Huihui, LIU Qi, ZHAO Ling, CAO Rong
2022, 18(2): 48-56.   doi: 10.12131/20210290
[Abstract](130) [FullText HTML](48) [PDF 961KB](11)
Chitooligosaccharides, which have a variety of biological activities, are the only known basic oligosaccharide widely used in food, agriculture and biomedicine. Chitosanases can cleave the β-1,4 glycosidic bonds in chitosan specifically to form chitooligosaccharides with different degrees of polymerization. Therefore, obtaining chitosanases with good stability is the key for the large-scale enzymatic preparation of chitooligosaccharides. In order to identify the amino acid sites affecting the pH stability of GH46 family chitosanases, the chitosanase from Bacillus sp. DAU101 (optimal pH 7.5) was selected as template and the chitosanase Csn-BAC from Bacillus sp. MD-5 as the research object. By combining homology modeling and sequence alignments, four candidate sites were selected, and the corresponding mutants were obtained (V1: P68A; V2: A137G; V3: A203M; V4: H234E). Compared with Csn-BAC, the thermal stabilities of four mutants showed varying degrees of reduction, while the pH stability was significantly improved. These results indicate that the selected amino acid sites have an obvious effect on pH tolerance, and this strategy is an effective way to modify the stability of chitosanase.
Metabolic engineering synthesis of neoxanthin, a key precursor of fucoxanthin
ZHANG Guilin, ZHANG Yating, JIANG Hong, LIU Zhen, MAO Xiangzhao
2022, 18(2): 57-65.   doi: 10.12131/20210316
[Abstract](91) [FullText HTML](35) [PDF 942KB](14)
Fucoxanthin is one of the common luteins in marine algae, especially in brown algae, which has antibacterial, anti-inflammatory, anti-obesity, anti-diabetes, anti-cancer, regulating intestinal flora, anti-organ fibrosis and other physiological activities. Neoxanthin is a possible precursor of fucoxanthin. In this paper, we constructed a neoxanthin synthesis pathway in Escherichia coli for the first time and the plasmid pTrc99a-crtEBIYZ, which carries five genes (crtE, crtB, crtI, crtY and crtZ) from Pantoea ananatis, and codes for proteins (geranylgeranyl pyrophosphate synthase, phytoene synthase, lycopene cyclase and β-carotene hydroxylase). We transferred the plasmid into E. coli, and obtained the zeaxanthin-producing E. coli BL21 pTrc99a-crtEBIYZ. The yield of zeaxanthin (dry cell mass) was 0.70 mg·g−1. We obtained E. coli pTrc99a-crtEBIYZ pACYCDuet-1-QZEP3 strain by transferring ZEP3 gene from Phaeodactylum tricornutum without signal peptide, and obtained E. coli BL21 NEO successfully by transferring the neoxanthin synthase gene NSY into E. coli BL21 pTrc99a-crtEBIYZ pACYCDuet-1-QZEP3. The concentrations of neoxanthin, violaxanthin and zeaxanthin were 99.27, 150.30 and 119.77 μg·g−1 dry cell mass, respectively.
Preparation and properties of medical compound hemostasis dressing from Pacific cod skin
SONG Xue, LIU Han, LI Zhaoxuan, LI Bafang, HOU Hu
2022, 18(2): 66-73.   doi: 10.12131/20210323
[Abstract](73) [FullText HTML](27) [PDF 1586KB](3)
In this study, an absorbable composite hemostatic dressing was prepared by combining sodium alginate with Pacific cod (Gadus macrocephalus) skin gelatin, and its mechanical properties, hemostatic effect, hemostatic mechanism and biocompatibility were evaluated. The results show that the composite hemostatic dressing had high mechanical strength with 1% of gelatin concentration. Results of hemostatic evaluation in vivo indicate that the dressing had good hemostatic effect on the femoral artery, liver wound and tail hemostasis models of rats, and the hemostatic time was (64±9), (108±4) and (230±25) s, respectively, which was similar with the hemostatic effect of commercial gelatin sponge. The dressing could shorten activated partial thromboplastin time (APTT) and thrombin time (TT), which activated endogenous coagulation and common coagulation pathway, and promoted the release of thromboxane-B2 (TXB2), platelet factor-4 (PF4) and P-selectin to achieve rapid hemostatic effect. Biocompatibility experiments show that the composite dressing had no acute toxicity or irritation and the hemolysis rate was less than 5%, which meets the standards of medical materials. The study provides reference and theoretical basis for developing new medical dressing and realizing high-value utilization of Pacific cod skin.
Preparation and characterization of S-nitrosated sodium alginate antibacterial hydrogel
YANG Xing, LIU Qiao, YU Dawei, TU Xiaoliang, TIAN Jinhuan, LI Lihua
2022, 18(2): 74-82.   doi: 10.12131/20210325
[Abstract](62) [FullText HTML](23) [PDF 3902KB](6)
Nitric oxide (NO) is a gas signaling molecule with high bacterial inhibition rate, which has been widely used in biomedical treatment. However, there are still problems such as poor biocompatibility of NO donor materials, low NO load, poor control release and slow-release effect. In this study, we used an aquatic polysaccharide material, sodium alginate (SA), to prepare sulfhydryl sodium alginate (SA-SH) and NO donor S-nitroso sodium alginate (SA-SNO), and prepared in-situ formed hydrogel by using different ratios of SA-SH and SA-SNO. The results show that the NO loading in the hydrogels increased with the increasing content of SA-SNO, and the release curve indicates that the gel possessed long-lasting release effects, wherein the releasing amount of NO arrived to 30.12−44.32 μmol·g−1 even after 5 d and the total release amount was 152−264 μmol·g−1. Additionally, antibacterial experiments show that the hydrogel had a significant inhibitory effect on Staphylococcus aureus and Escherichia coli. In summary, the composite hydrogel has the potential application as an anti-bacterial wound dressing.
Effect of carboxymethyl agar on gel properties of tilapia surimi
QI Bo, YANG Shaoling, WANG Yueqi, HU Xiao, YANG Xianqing, PAN Chuang, LI Laihao, WANG Lunan
2022, 18(2): 83-89.   doi: 10.12131/20210311
[Abstract](61) [FullText HTML](23) [PDF 1418KB](8)
We added different doses of carboxymethyl agar (CMA) to tilapia (Oreochromis niloticus×O. areus) surimi to investigate the effects of CMA on the gel properties of tilapia surimi based on the indexes such as surimi gel strength, water holding capacity, texture characteristics, color, protein chemical composition and microstructure. The results show that CMA could significantly increase the gel strength of surimi gel with the addition of 0.5%−2.0% CMA (P<0.05), reaching the maximum value of 70.7%. The water holding capacity, texture characteristics and whiteness could be improved significantly by adding 1.5%−2.5%, 1.5%−2.5% and 0.5% CMA, respectively (P<0.05). CMA had a significant effect on the chemical force of surimi protein (P<0.05), showing that moderate addition of CMA destroyed the ionic bond, promoted the formation of hydrogen bond, hydrophobic bond and disulfide bond, and promoted the gelation of surimi. SDS-PAGE electrophoresis and scanning electron microscopy analysis show that CMA promoted the cross-linking of myosin heavy chains (MHC), and the addition of 1.5% CMA could make the surimi gel form a uniform and dense network structure. In conclusion, moderate addition of CMA to tilapia surimi affected the water absorption, chemical force and protein thermal aggregation behavior of the surimi, enhanced the crosslinking effect of protein, improved the network structure of surimi gel, and reformed the gel properties of surimi.
Effect of carrageenan on quality of low-sodium noodles
HU Zining, MAI Shixue, LU Wei, FANG Yapeng
2022, 18(2): 90-97.   doi: 10.12131/20210334
[Abstract](139) [FullText HTML](29) [PDF 1266KB](11)
To study the effect of seaweed polysaccharide carrageenan on the sensory properties and overall quality of low-sodium noodles, we designed the noodles containing low-sodium salts with different formulas and carried out a sensory evaluation experiment, so as to analyzed the color, cooking time, texture and microstructure of the noodles. The results show that the addition of carrageenan covered the metallic bitterness caused by potassium chloride in noodles effectively. Carrageenan showed no significant influence on the optimal cooking time of noodles (P>0.05), but changed the color of noodles after the noodles having been cooked to a certain extent and improved the hardness, springiness and chewiness of noodles. Scanning Electron Microscope (SEM) analysis demonstrates that carrageenan made the microstructure of noodles more compacted after the cooking but did not show obvious influence on the microstructure of noodles before the cooking. The results suggest that carrageenan can reduce the bitterness caused by potassium chloride salt substitute but maintain the quality of noodles, achieving a high-efficiency salt reduction (up to 50%) in noodles, which proposes a new idea for the potassium chloride-based salt substitutes in food industry.
Mutation and selection of high squalene production yeast Pseudozyma sp. induced by carbon-ions beam irradiation and its electrotransfor-mation
XIAO Yan, WANG Lu, WANG Sen, CONG Peihu, LU Dong, FENG Yingang, CUI Qiu, SONG Xiaojin
2022, 18(2): 98-104.   doi: 10.12131/20210294
[Abstract](70) [FullText HTML](18) [PDF 1134KB](9)
In order to improve the yield of squalene, using Pseudozyma sp. SD301 as the starting strain, we selected the mutant strain with high squalene yield by carbon-ions (12C6+) beam irradiation technology, and optimized the electrotransformation conditions of the mutant strain. We used 100 μmol·L−1 H2O2 as the screening pressure. When the carbon heavy ion beam irradiation dose was 120 Gy, the mutant PS120 was obtained with higher squalene yield than the original strain. After 3 days of culture, the squalene yield of the mutant reached 1.33 g·L−1 and the squalene mass reached 41.31 mg·g−1. The green fluorescent protein EGFP was used as the characterization marker to optimize the electrotransformation conditions of PS120. The results of enzyme digestion, electrophoresis and sequencing show that the gene encoding EGFP could be successfully transferred into PS120 cells under 900 V voltage. The high-level expression of EGFP protein in PS120 cells was further confirmed by laser confocal microscope.
Process optimization and quality analysis of Siniperca chuatsi fermentation based on mixed bacteria fermentation
WU Yanyan, WANG Yueqi, SHEN Yingying, CHEN Qian, LI Chunsheng, ZHAO Yongqiang, YANG Shaoling, PAN Chuang, LI Laihao
2022, 18(2): 105-114.   doi: 10.12131/20210296
[Abstract](130) [FullText HTML](36) [PDF 1625KB](9)
In order to explore the technology of artificial inoculation with mixed bacteria fermention for mandarin fish (Siniperca chuatsi), to improve the extensive and empirical processing mode and to ameliorate the quality of traditional fermented S. chuatsi, we optimized the fermentation process conditions (fermentation temperature, fermentation time, strain ratio and starter inoculation amount) inocuted with mixture starter by single factor and response surface tests. Then we determined the moisture, pH, amino nitrogen, total acid, thiobarbituric acid reactive value (TBARS) and total volatile base nitrogen (TVB-N) content and compared them with traditional natural fermented fish, so as to investigate the effect of inoculation fermentation on its quality. The optimal fermentation process for S . chuatsi was obtained (mass ratio of Pediococcus pentosaceuLactobacillus sakeiStaphylococcus carnosus of 1∶1∶3; inoculum of 1.0%; fermentation temperature of 22 ℃; fermentation time of 4 d). Compared with naturally fermented S. chuatsi, the mass fractions of moisture and pH of the inoculated mixed starter fermented fish decreased by 2.04% and 0.46%, respectively. In a shorter fermentation time, its mass fraction of amino nitrogen was similar with that of naturally fermented fish, and the mass fraction of total acid increased by 29.27%. The mass fractions of TBARS and TVB-N decreased by 35.00% and 53.10%, respectively. In conclusion, the inoculated mixed starter culture fermentation of S. chuatsi helps to improve its quality and safety, shorten the fermentation time, and control the fermentation process.
Improvement effect of Halanaerobium fermentans YL9-2 on quality and flavor of fish sauce during fermentation
LI Wenjing, LI Chunsheng, WANG Yueqi, CHEN Shengjun, ZHAO Yongqiang, WU Yanyan, LI Laihao
2022, 18(2): 115-123.   doi: 10.12131/20210314
[Abstract](47) [FullText HTML](32) [PDF 855KB](5)
In order to solve the problems of long fermentation period and difficult flavor control of traditionally fermented fish sauce, we screened a salt fermenting anaerobic bacterium (Halanaerobium fermentans) YL9-2 related to the flavor formation of traditional fish sauce from the fermentation broth of traditional fish sauce. The results show that YL9-2 could increase the content of amino acid nitrogen and shorten the quality formation time in fish sauce significantly. Meanwhile, its addition improved the food safety of fish sauce significantly, and the mass concentrations of histamine, tyramine, putrescine, cadaverine, tyramine and total biogenic amine decreased by 26.4%, 27.1%, 9.4%, 39.8%, 69.4% and 25.7% at the end of the fermentation. Besides, we applied headspace solid-phase microextraction gas chromatography-mass spectrometry to analyze the volatile flavor compounds in fish sauce. A total of 38 volatile compounds were identified. At the end of the fermentation, the concentrations of isovaleraldehyde, 2-methylbutanal, hexanal, heptanal, n-octanal, n-nonanal, 1-pentene-3-ol, 1-octen-3-ol, 2-nonone and 2-hendecanone respectively increased by 79.7%, 92.5%, 45.3%, 41.8%, 21.2%, 29.4%, 20.4%, 46.6%, 67.7% and 47.2%, which enhanced the malt, grass, cheese, fruit, mushroom, sweet and fatty flavors of fish sauce significantly. The trimethylamine concentration decreased by 61.7% compared with that during natural fermentation, significantly reducing the fishy taste of fish sauce. The results provide important technical supports for the targeted improvement of the quality, flavor and food safety of traditionally fermented fish sauce.
Effects of inoculation of Lactiplantibacillus pentosus and Saccharomyces cerevisiae on quality of low-salt fermented bream
TIAN Xuyan, GAO Pei, XIA Wenshui, XU Yanshun
2022, 18(2): 124-133.   doi: 10.12131/20210321
[Abstract](67) [FullText HTML](28) [PDF 887KB](6)
In order to improve the flavor and safety quality of low-salt fermented fish, we inoculated bream (Parapraxis pekinensis) with Lactiplantibacillus pentosus (Lp-1) and Saccharomyces cerevisiae (Sc-2018), so as to study the effects of inoculating microbial strains on the quality of low-salt fermented bream based on the indexes of pH, volatile basic nitrogen (TVB-N), microorganisms, TCA-soluble peptides, biogenic amines and volatile flavor compounds. Results show that compared with the control group, inoculation of Lp-1 and Sc−2018 could inhibit the production of volatile basic nitrogen and biogenic amines effectively, promote the degradation of protein and the formation of volatile flavor compounds such as ethyl acetate and 3-hydroxy-2-butanone. Inoculation of Lp-1 could promote the growth of lactic acid bacteria and reduce the pH of fermented bream appropriately. Compared with the other two groups, inoculation with lactic acid bacteria could reduce the biogenic amine content of fermented bream siginificantly (P<0.05), which improves the edible safety and the flavor of bream.
Mixotrophic and carbon fixation culture of nervonic acid-producing microalgae Mychonastes afer
SHI Xiaoyi, DING Xiaoting, WAN Zixuan, YING Yu, LI Fuli, GAO Xin, FAN Yong
2022, 18(2): 134-141.   doi: 10.12131/20210307
[Abstract](67) [FullText HTML](47) [PDF 702KB](11)
Microalgae are a group of single cell microorganism, which play an important role in aquatic production such as aquatic feeding and water regulating. This research focuses on the growth and photosynthetic capacity of Mychonastes afer and Chlorella sorokiniana under different nutrition and aeration conditions. The microalgae were cultivated under autotrophic, mixotrophic or heterotrophic conditions, respectively. And the influence of CO2 concentration was also investigated. The growth curve, photosynthetic electron transfer rate, organic carbon source utilization, photosynthetic oxygen evolution and respiratory oxygen consumption rate were measured to inflect the differences between M. afer and C. sorokiniana, and the emphasis was given to lipid components of M. afer. The results show that C. sorokiniana could grow under heterotrophic condition without light, while M. afer could not. The photosynthetic system of the two species were both inhibited by organic carbon sources, displaying lower efficiency of photosynthetic electron transfer rates and slower photosynthetic oxygen evolution rates. Besides, it is found that under mixotrophy condition, high concentration of CO2 was beneficial to the growth of M. afer, which promoted cell utilization of glucose, and increased the production of lipid and nervonic acid. The study explores a mixotrophic condition for M. afer to produce natural nervonic acid, shows significant differences between the two algae species in photosynthetic system, and explores the cooperative utilization of external organic carbon sources.
Comparative research of plant hormones and alginate oligosaccharides in seaweed extracts by different processing methods
MIAO Junkui, ZHANG Yating, ZHANG Shengguo, ZHENG Zhihong, WANG Zhipeng, WANG Haiying
2022, 18(2): 142-149.   doi: 10.12131/20210287
[Abstract](108) [FullText HTML](31) [PDF 621KB](6)
In seaweed (Laminaria japonica) extraction processing, biological enzymolysis processing has been an ideal alternative to traditional chemical extraction method. In order to evaluate the extraction effects of three different processing methods, we treated the seaweed by chemical processing (CP), enzymolysis processing (EP) as well as combined enzymolysis and microbial fermentation processing (CEMP). Besides, we compared the contents of plant hormones and algiante oligosaccharides in addition to the molecular mass distribution in three kinds of seaweed extracts. We determined the alginate content, molecular mass of alginate oligosaccharide and plant hormones contents by m-hydroxydiphenyl method, HPLC and HPLC-MS, respectively. The results show that the CP method had the lowest extraction rate of alginate oligosaccharides (41.99%) with molecular mass of 200−400 D, while the EP method and CEMP method had relatively higher extraction rate of alginate oligosaccharides (90.75% and 82.21%) with molecular mass of 200−1 600 D. Indoleacetic acid (IAA) was the most abundant plant hormone among all the three extracts, ranging from 2.64 to 64.59 ng·g−1, followed by jasmonic acid (JA, 0.05−13.09 ng·g−1). The plant hormone content of the extract by CEMP method was higher than that of the other two extracts. Based on the comprehensive comparison of extraction rate of plant hormones and alginate oligosaccharides, the CEMP method is more suitable for the preparation of agricultural seaweed extract than the CP method and EP methods.
Effect of different molecular weight chitosan coating on preservation of fish fillets during refrigerated storage
ZHAO Wenyu, YU Dawei, DONG Junli, XIA Wenshi, LI Lihua
2022, 18(2): 150-157.   doi: 10.12131/20210333
[Abstract](130) [FullText HTML](54) [PDF 753KB](6)
In order to explore the differences in the effect of different molecular weight (Mw) chitosan coatings (50, 200 and 500 kD) on the quality of refrigerated grass carp (Ctenopharyngodon idella) fillets, we applied the biological, physical and chemical methods to detect the fresh-keeping quality of the fish fillets, and compared the changes in the sensory scores, microbial enumeration [total viable count (TVC) and Pseudomonas count], and physicochemical indicators [shear force, water loss rate, pH, total volatile base nitrogen (TVB-N), TCA-soluble peptides and biogenic amines] during the storage of different coating samples. The results show that compared with the control group, the coating treatments with all the three Mw chitosan coatings could inhibit the deterioration of fillets quality effectively. Combining with the results of sensory evaluation, TVB-N and TVC, the shelf life of the control group was less than 6 d, while the coating treatment could extend the shelf life more than at least 2 d, and especially the sensory quality of fillets with 200 kD Mw chitosan coating remained the best and had the longest shelf life during the storage. By comparing the microbial and physicochemical indexes of the three coated groups, we found that the total viable count (TVC), Pseudomonas count, shear force, juice loss rate, TVB-N and putrescine content of 200 kD Mw chitosan coating on the 8th day of storage were better than those of the other two groups. Thus, 200 kD Mw chitosan coating could be used as a preferred coating material for the preservation of fresh fish meat.
Study on optimization parameters of spray drying and quality evaluation of Channa argus head soup drying product
GAO Ruichang, ZHANG Wei, LI Xin, SU Li, YUAN Li
2022, 18(2): 158-164.   doi: 10.12131/20210309
[Abstract](48) [FullText HTML](37) [PDF 614KB](15)
In order to meet consumers' demand for delicious fish soup products, and improve the utilization value of Channa argus processing by-products, we prepared the fish head soup by spray drying method using C. argus head soup as raw material and maltodextrin as a drying aid. The optimization of spray drying technology was carried out by analyzing the water mass fraction, color, solubility, bulk density, time of punching and viscosity of dry powder. The results show that maltodextrin could increase the spray drying rate, powder brightness and solubility effectively, and improve the adhesive condition. With the maltodextrin addition amount of 15 g·L 1, spray drying inlet temperature of 170 ℃ and feeding speed of 6 mL·min 1, the spray effect and product quality were the best. The prepared fish head soup powder contained low water content, large packing density, high solubility, low moisture absorption and uniform particle size. In conclusion, spray drying method can be used as a preparation method for fish head soup.
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Species identification and morphology of fish eggs from Jiangmen coastal waters in spring using DNA barcoding
CHEN Jing, HUANG Delian, WANG Xuehui, XU Lei, ZHANG Jian, LI Yafang, NING Jiajia, WANG Lianggen, LIU Shuangshuang, LIN Zhaojin, DU Feiyan
 doi: 10.12131/20220028
Jiangmen is located in the southwest of the Pearl River Estuary. It is the spawning ground and nursery ground for a variety of small fish.To identify the species of fish eggs from Jiangmen coastal waters of the Pearl River Estuary in sping based on DNA barcoding analysis, we described and preliminarily classified the morphological characteristics of fish eggs. We acquired a total of 13 taxa, which belonged to three orders and ten families. Four and eight taxa were identified to species and genus levels, respectively (Ambassis gymnocephalus, Gerres limbatus, Sillago sihama, Cynoglossus puncticeps, Sardinella sp., Stolephorus sp., Acanthopagrus sp., Alepes sp., Johnius sp., Sillago sp. and Cynoglossus sp.). One taxon was identified in family's Leiognathidae sp.. The results demonstrate that most fish eggs collected in the survey area can be classified by morphological characteristics such as shape, fish eggs size, perivitelline space, number, and pigment distribution of oil globules. In addition, the colour, amount and distribution of pigments on the embryo are also important in species identification when the embryo is well developed. However, it is difficult to distinguish the closely related species only by the morphological characteristics of a single developmental stage. Further morphological studies should be conducted in the future.
Molecular cloning and characterization in immune response of two C-type lectin genes (SaCD302 and SaMBL) from Symphysodon aequifasciatus
MA Tengfei, WEN Bin, LIU Xin, MIAO Lin, GAO Jianzhong, CHEN Zaizhong
 doi: 10.12131/20220018
Symphysodon aequifasciatus has a unique parental rearing behavior. In the previous study, two C-type lectins (CTLs) were found to be highly expressed in the skin of the parent fish, but with different expression patterns. In order to investigate the difference in the potential immune functions of the specific CTLs, we cloned two CTL genes (SaCD302 and SaMBL), then simulated and analyzed their immune esponse patterns under pathological infection. The results show that the ORF region of SaCD302 and SaMBL were 741 and 795 bp in length, encoding 246 and 264 amino acids (aa), respectively. The SaCD302 sequence contained a signal peptide (aa 1–29), a C-type lectin-like domain (CTLD) (aa 32–169) and a transmembrane domain (aa 184–206). Two low complexity regions (aa 32–92 and aa 104–121) and a CTLD (aa 137–263) were expressed in SaMBL sequence. Moreover, SaCD302 and SaMBL shared the highest similarity with that of Archocentrus centrarchus. SaCD302 was highly expressed in the head kidney, followed by the liver and gill. Compared with the intestine, liver, spleen and gonads, the skin had the higher expression of SaMBL. After Aeromonas hydrophila infection, SaCD302 expression was significantly upregulated in the spleen, head kidney, intestine and skin, while SaMBL was only upregulated in the head kidney, intestine and skin, and these two genes were expressed in different temporal manners, indicating that they might play different roles in the immune defense of S. aequifasciatus.
Embryonic development and morphological characteristics of larvae and juvenile of Platax teira
LIU Mingjian, GUO Huayang, GAO Jie, ZHU Kecheng, LIU Baosuo, GUO Liang, ZHANG Nan, YANG Jingwen, LIU Bo, ZHANG Dianchang
 doi: 10.12131/20210251
In order to improve the egg hatching rate and fry survival rate of Tiera batfish (Platax teira), and to provide a theoretical basis for artificial spawning and fry breeding, we observed and analyzed the temporal characteristics of embryonic and juvenile development of fertilized eggs of P. teira, and measured the morphological indexes to derive the regression equations for the growth characteristics of juvenile stages. The results show that the eggs were floating, (1.29±0.09) mm in diameter, with a tough, transparent, yellow spherical shell and a single oil globule that was not sticky. At an incubation temperature of (26±0.3) ℃, salinity of 34–36 and pH 7.8±0.5, the embryos underwent seven stages of development for 27 periods, taking 27 h 45 min. The total length of newly hatched larvae were (3.120±0.349) mm, transparent, with a large amount of branched lutein scatterring on the surface of the body, followed by the juvenile stage (0–17 d) and the larval stage (17–25 d). The juvenile stage was 25 d later, when the fin spines and fin ray were fully developed, typically with three black bands on the head, trunk and tail, and a snowy silvery body color. Statistical models show that the early stages of growth were slow, but accelerated after 7 dah. At 8 dah, the juveniles showed feeding and aggressive behavior.
Evaluation of genetic parameters for growth and comprehensive stress tolerance traits of Litopenaeus vannamei
WANG Lun, WANG Chongyi, LIU Jianyong
 doi: 10.12131/20210252
To enrich the growth and stress resistance database of Litopenaeus vannamei, and to provide scientific reference for the genetic improvement of its growth and comprehensive stress tolerance. We took five L. vannamei populations with different genetic backgrounds as parents, among which "Xinghai 1" (GS-01-007-2017) was the core population and the other four populations were introduced from Thailand and the United States. Eighty full-sib families had been obtained through mating and 38 families finally retained. We then used multi-trait animal model and ASReml 4 software to estimate the variance components and genetic parameters of growth and comprehensive stress tolerance of L. vannamei P105 under the combined stress of high salt (35), low pH (6±0.1), and high ammonia nitrogen (70 mg·L−1). The results show that the heritability of growth traits was high (0.37±0.09)−(0.51±0.10), and the heritability of comprehensive stress tolerance traits was medium (0.21±0.06). The results show that it is feasible to improve the growth traits and comprehensive stress tolerance traits by breeding. The genetic correlation of growth traits (including body mass, body length, head breastplate length, and full length of the abdomen) was generally high, ranging from (0.54±0.13)−(0.99±0.01) (P<0.01). The extremely significant correlation between growth traits shows that any growth trait could be replaced by other growth traits for indirect selection. The genetic correlation between growth traits and comprehensive stress tolerance traits was low to medium positive correlation (0.11±0.23)−(0.39±0.19), indicating that the comprehensive stress tolerance traits can also be indirectly improved when breeding with growth traits as the main selection target.
A study on spatial-temporal distribution and marine environmental elements of Symplectoteuthis oualaniensis fishing grounds in outer sea of Arabian Sea
XIAO Ge, XU Bo, ZHANG Heng, TANG Fenghua, CHEN Feng, ZHU Wenbin
 doi: 10.12131/20210217
In order to understand the development status of fishery resources in the waters off the Arabian Sea in the high seas of the northwest Indian Ocean, and to explore the fishery distribution of Symplectoteuthis oualaniensis and the impact of fishery environmental factors on its resources, we carried out two sea surveys in the waters off the Arabian Sea, obtained the data of catch and operating water temperature at each survey site, and used the Generalized Additive Model (GAM) analyzed the impact of various marine environment and tempo-spatial factors on the catch per unit effort (CPUE) of S. oualaniensis in that sea area. The results show that: 1) There are mainly three areas with high CPUE values (60°E−61°E, 16°N; 62°E, 16°E−18°N; 61.50°E−63°E, 17°N−17.75°N). 2) The influencing factors of the best GAM model included latitude and longitude, lunar calendar day, sea surface temperature (SST), chlorophyll a concentration (Chl a) and sea surface temperature anomaly (SSTA). The top three explanatory factors with the highest explained variance were longitude and latitude, lunar calendar day and SSTA. 3) The total number of catch on the no-moonlight night was 1.38 times the number of catch on the bright moonlight night, and the total catch of the no-moonlight night was 108.21% higher than the total catch of the bright moonlight night. 4) According to the GAM model, the optimal SST range was 26.5−27.5°C; the Chl a concentration range was 0.30~0.50 mg·m−3; the SSTA range was 0−0.4°C.
Cloning and expression profiling of Cyp1a gene in Lutjanus argentimaculatus under 4-bromodiphenyl ether (BDE-3) and decabromodiphenyl ether (BDE-209) exposure
ZHANG Zhe, GONG Xiuyu, LAN Lili, WANG Xuefeng, MA Shengwei, CHEN Haigang, ZHANG Linbao
 doi: 10.12131/20210271
Cytochrome P450 enzymes (CYPs) are encoded by P450 genes, in which cytochrome P450 1A (Cyp1a) genes mainly involve in biotransformation and metabolism of numerous xenobiotics. In this study, we cloned the Cyp1a gene from Lutjanus argentimaculatus, and investigated its tissue expression pattern. In addition, we evaluated different concentrations (10, 50 and 250 μg·L−1) of BDE-3 and BDE-209 on Cyp1a gene profile and 7-ethoxyresorufin-O-deethylase (EROD) activity in liver of L. argentimaculatus. The results show that the full length of Cyp1a cDNA was 2 540 bp with 1 566 open reading frame encoding 521 amino acids. The sequence homology of L. argentimaculatus CYP1A was the highest (92.69%) with that of Lateolabrax maculatus. Phylogenetic analysis results indicate that CYP1A was closely aligned with Sander lucioperca protein. Cyp1a transcripts were most abundant in liver, followed by brain and gill, but lowest in muscle. 10 μg·L-1 of BDE-3 and BDE-209 showed no effects on both Cyp1a expression and EROD activity, while high concentrations (50 and 250 μg·L-1) of BDE-3 down-regulated both of them significantly in a concentration-dependent manner on 7th-15th day. In contrast, exposure to 50 and 250 μg·L-1 of BDE-209 resulted in the increase in hepatic Cyp1a level and EROD activity. Moreover, Cyp1a genes levels and EROD activities showed a good correlation. High concentrations of BDE-3 and BDE-209 can affect Cyp1a gene expression in liver of L. argentimaculatus in different manners.
Analysis of solid-state anaerobic fermentation process of mackerel processing by-products by high-throughput sequencing
WANG Yao, LI Hongyu, QI Xiangming, MAO Xiangzhao, DONG Hao, GUO Xiaohua
 doi: 10.12131/20210285
In order to develop commercial technology for the comprehensive utilization of mackerel (Pneumatophorus japonicus) processing by-product, we carried out the non sterilized solid-state anaerobic fermentation of mackerel by-products to produce a novel protein source for feed with bioactivity. In addition, we monitored the content of histamine, acid-soluble protein and other indexes such as pH, total volatile basic nitrogen and antigenic protein; and investigated the evolution of microbial community during the fermentation by high-throughput sequencing technology, comparing the free amino acids and fatty acids before and after the fermentation. The results show that Lactobacillus plantarum HSCC-LP121 had the best comprehensive effect in increasing acid soluble protein content, reducing histamine accumulation and reducing volatile base nitrogen production. After 30 d of fermentation, the histamine content decreased to 0.629 g·kg−1, which indicates that HSCC-LP121 had the ability to degrade histamine. Moreover, HSCC-LP121 inhibited the growth of potential histamine-producing microorganisms such as Psychrobacter and Pseudomonas. Besides, the strain could also inhibit the growth of potentially harmful fungi such as Aspergillus, and induce the growth of some aroma-producing yeasts.
Fish stock assessment based on abundance index and resilience: a case study of largehead hairtail in Sea of Japan and East China Sea
 doi: 10.12131/20210213
In order to understand the exploitation status of largehead hairtail (Trichiurus japonicus) fisheries in the Sea of Japan and the East China Sea, we used a fishery assessment model based on abundance index (abundance maximum sustainable yields, AMSY) to assess the two fisheries. The results show that during most of the 1990s and 2000s, the relative biomass levels (B/BMSY) of the largehead hairtail fisheries in the two seas were lower than 1, but the relative fishing mortality levels (F/FMSY) were higher than 1, which indicates an overfished state. The estimated parameters such as relative maximum sustainable yield (MSYq) and relative fishing mortality at MSY level (FMSY) of the AMSY model were more sensitive to different prior distribution ranges of intrinsic rate of increase (r), while the estimated biological reference points (BRPs), i.e., F/FMSY and B/BMSY were more sensitive to the lower limit of different prior distribution ranges of relative biomass level (Bt/k). AMSY can estimate the BRPs of the target fisheries under MSY framework using only catch per unit effort (CPUE) data, prior information of r and relative biomass level for a specific year. AMSY is appropriate for fishery stock assessment in the sea areas where lack statistical data of catches.
Comparative analysis of nutritional composition and energy density of muscle in three geographical populations of Megalobrama terminalis
LIU Yaqiu, LIU Mingdian, LI Xinhui, LI Jie
 doi: 10.12131/20210226
In order to compare the nutritional composition and energy density of Megalobrama terminalis populations in Wangquan River, Moyang River and Xijiang River, we applied the biochemical analysis methods to determine the contents of moisture, crude protein, ash and crude fatty, as well as amino acid and fatty acid composition and energy density of the muscle of three M. terminalis populations. The results indicate that the Xijiang River population had the highest crude protein mass fraction [(20.2±0.5)%], while Wangquan River population had the highest water mass fraction [(79.0±0.5)%]. The energy density of Xijiang River population was significantly higher than that of Wangquan and Moyang River populations (P<0.05). The essential amino acid index (EAAI) of Xijiang River population was higher than that of Wanquan and Moyang River populations. We had detected 23 kinds of common fatty acids in the muscle of three M. terminalis populations. The content of monounsaturated fatty acid (MUFA) in the muscle of Wanquan River population was the lowest, while the content of polyunsaturated fatty acids (PUFA) of Wanquan River populatin was the highest. The DHA content in muscle of Xijiang River population was much higher than that of Wanquan and Moyang populations. Potassium (K) and copper (Cu) had the highest and lowest contents among all the mineral elements in the muscle of three M. terminalis populations, respectively. The contents of ferrum (Fe) and manganese (Mn) of Xijiang River population were significantly higher than those of Moyang and Wanquan River populations, but the content of zinc (Zn) of Xijiang River population was much lower than those of Moyang River population.
Analysis of bacterial community and diversity in gill tissues of bony fishes in adjacent South China Sea
GUO Yingxiang, YANG Liling, XU Youwei, FANG Yifei, WANG Meng, JIANG Jingzhe
 doi: 10.12131/20210247
Focusing on the abundant fishery resources in the South China Sea, we analyzed the distribution characteristics of the microbial community in the gill tissue of bony fishes in the adjacent South China Sea by using 16S amplicon sequencing technology. In addition, we discussed the differences in the bacterial community structure at different sites. The results show that the sequencing obtained a total of 2 952 366 effective spliced fragments (Clean Tags) with an average of 56 776 in each library. The dominant taxa were analyzed at phylum and genus levels. Proteobacteria was the highest (71.3%) at phylum level, and Acinetobacter was the highest at genus level (17.2%). The alpha diversity of different sites was significantly different, and the I9 and H8 sites had the highest species richness (Chao1 index), and the D3 site had the highest diversity (Shannon index). The beta diversity of samples from different sites was significantly different (P<0.05), but there was no significant difference between the host classification (order level) groups (P>0.05). The composition of bacterial communities in the gill tissues of bony fishes in the South China Sea was abundant. Compared with the classification of the host, the sampling station has more important influence on the community of the bacterial in the gill tissues, and may play an active role in assisting the host's nutrient transport and metabolism.
Study on extraction, identification and stability of UV resistant MAAs from Porphyra haitanensis in cosmetics system
XU Feng, CHEN Deke, CHEN Xiaogang, NIE Jinmei, MA Zhihao, SUN Huili, CHEN Xin
 doi: 10.12131/20210244
Taking Porphyra haitanensis as raw material, we extracted the mycosporine-like amino acids (MAAs) and charaterized them by UV Vis spectroscopy and Liquid Chromatograph-Mass Spectrometer (LC-MS), so as to study the effects of various factors in the cosmetic system (pH, light, temperature, preservatives, antioxidants and functional additives) on the stability of MAAs. The results show that Shionrine and Porphyra-334 were the main MAAs in P. haitanensis. MAAs had the highest stability in the weak acid environment with pH=6. UV irradiation for 10 h could decrease the absorbance value by 94.4%. After having been placed at 48 ℃ for 56 d, its absorbance value decreased by 28.3%. At 48 ℃, the addition of small peptide and hyaluronic acid increased the absorbance value of the solution by 82% and 18.6%, respectively, which could improve the stability of MAAs compounds significantly. Other commonly used preservatives, antioxidants and functional additives had no significant effects on the stability of the MAAs.
Effect of salinity on embryonic development and post-embryonic larval growth of Pramisgurnus dabryanus
CHEN Jianhua, LI Xue, ZHAO Jian, ZHU Honggeng, WANG Haihua, ZHU Ming
 doi: 10.12131/20210230
In order to understand the adaptability of embryo and larvae of Paramisgurnus dableanus to salinity, we bred the gastrula embryos in water at salinity of 0, 2, 4, 6, 8 and 10, then investigate the effect of salinity on the hatching period, hatching rate, abnormality rate, survival rate, specific growth rate (SGR), yolk sac absorption and survival activity index (SAI). The results show that: 1) The incubation period was significantly shorter than that of the control group at salinity of 2 and 4 (P<0.05). The incubation rate was highest at salinity of 4, not significantly different from the control group (P>0.05). 2) The abnormality rate of the newly hatched larvae increased with the increase of salinity, while the survival rate of larvae of 3 dah (days after hatching) decreased. 3) The total length of newly hatched larvae decreased first and then increased, while that of larvae of 3 dah decreased with the increasing salinity. The SGR and yolk sac absorption rate increased first and then decreased. 4) The survival activity index (SAI) of the larvae increased first and then decreased with the increase of salinity, and reached the maximum at salinity of 4. These results indicate that the optimal salinity for embryo development and larval growth of P. dableanus is 0−4.
Construction and characterization research of essA, essB and essC-deleted mutants of Streptococcus agalactiae
MA Yanping, HAO Le, FENG Guoqing, LIANG Zhiling, MA Jiangyao, KE Hao, LIU Zhenxing
 doi: 10.12131/20210246
The membrane proteins are critical to substrate protein secretion in VII secretion system existing in Streptococcus agalactiae. In this study, we constructed the membrane proteins knockout vectors with chloramphenicol tag including pSET4s-ΔessA, pSET4s-ΔessB and pSET4s-ΔessC, and transformed them into electrocompetent S. agalactiae strain WT. After the homologous recombination, we screened the mutant S. agalactiae ΔessA, ΔessB and ΔessC via PCR assays. Based on the growth curve analysis, S. agalactiae ΔessA, ΔessB and ΔessC strains showed significantly slower growth process than WT. ΔessA and ΔessB strains had significant difference in early stage of growth compared with WT strain (P<0.01). According to the secretion product analysis of ESAT6 protein, S. agalactiae ΔessA, ΔessB and ΔessC strains showed significantly lower ESAT6 product than WT (P<0.01). According to challenge test analysis, the deletion of essA, essB or essC gene significantly reduced virulence of S. agalactiae ΔessA, ΔessB and ΔessC compared with WT (P<0.01). The results suggest that essA, essB and essC proteins are important component membrane proteins of VII secretion system in S. agalactiae, and these genes deletions cause ESAT6 mRNA expression and virulence decline.
Geostatistics-based study on spatial-temporal distribution of Auxis thazard in South China Sea
ZHOU Xingxing, FAN Jiangtao, YU Jie, XU Shannan, CAI Yancong, CHEN Zuozhi
 doi: 10.12131/20210327
In this study, we analyzed the spatial-temporal distribution characteristics and ecological dynamics of Auxis thazard by geostatistical methods based on the data from the light mask fishery survey conducted in the South China Sea from 2016 to 2017. The results show that the distribution of A. thazard in the South China Sea was mainly low-density, and there were few high-density sea areas. The seasonal aggregation characteristics of A. thazard in offshore shallow waters were obvious, and the resource density index followed a descending order of summer>spring>autumn. The spatial distribution of A. thazard fishery had strong spatial heterogeneity, with the proportion of spatial structure over 75% in four voyages. The spherical model was the main variation model, and the average main variation range was 1.861 0°. The A. thazard in the South China Sea was obviously characterized by southwest-northeast migration, and its spatial layout had a patch-like spatial distribution. The results can better reflect the spatial-temporal distribution characteristics of the A. thazard fishery in the South China Sea, which provides scientific basis for its fishery analysis and management.
An investigation of large-size light falling-net fishing vessels operating in South China Sea based on Beidou VMS data
QIAN Jing, LI Jiajun, CHEN Zuozhi, MA Shengwei, ZHANG Peng, QIU Yongsong, CAI YanCong
 doi: 10.12131/20220001
Beidou vessel monitoring system (VMS), which can be used to monitor fishing operations of the vessels, has the potential to provide scientific foundation for management of the fishery. We explored the large-size light falling-net fishery in the South China Sea based on VMS data in 2018. The Beidou VMS obtained a total of 8 821 681 records of 121 vessels from Guangdong, Guangxi and Hainan Provinces, with an average of 406 records per vessel per day. There is difference in the frequency of Beidou VMS transmission among the vessels from different provinces, and VMS signals were more frequently transmitted when a vessel was operating in the open South China Sea than when it was fishing along the coast. The vessels mainly operated fishing in the Nansha Islands in spring, off the Pearl River mouth in summer, and in the Beibu Gulf and Zhongsha and Xisha Islands waters in autumn and winter. In 2018, the vessels operated 19 986 fishing days in the South China Sea, decreasing from 7 768 d (38.87%) in spring, 4 738 d (23.71%) in autumn, 4 406 d (22.05%) in winter to 3 074 d (15.38%) in summer. Moreover, we discussed the advantages and disadvantages of Beidou VMS in monitoring the large-size light falling-net vessels. It is showed that using Beidou VMS to study the large-scale light falling-net vessel in the South China Sea can monitor their spatial distribution and dynamic changes quickly and comprehensively.
Effect of low-temperature acclimation on survival, non-specific immune and antioxidant indexes of Epinephelus fuscoguttatus ♀×E. lanceolatus
YUAN Zhongjin, CEN Jianwei, LI Laihao, YANG Xianqing, HUANG Hui, WEI Ya, HAO Shuxian, ZHAO Yongqiang, WANG Yueqi
 doi: 10.12131/20220042
In order to obtain the best acclimation temperature conditions for Epinephelus fuscoguttatus ♀×E. lanceolatus ♂, we decreased the water temperature to 24, 20, 18 and 16 ℃ at the rate of 0.5−1 ℃·h−1, then recorded the physiological responses and survival time, as well as the changes of water quality, non-specific immune index and antioxidant indicator. The results show that the survival time of the grouper increased with the decrease of temperature within the range of 24−16 ℃. When the water temperature was maintained at 16 ℃, the concentration of total ammonia nitrogen (TAN) increased slowly, and the survival time was the longest, up to 109 h. The non-specific immune and antioxidant parameters changed after the grouper being cultured at different temperatures for 48 h. Compared with control group, the contents of complement protein 3 (C3), globulin (GLB) and total protein (TP) increased in 16 ℃ group significantly, while the other indexes had no significant changes. The activities of superoxide dismutase (SOD) and catalase (CAT) in the liver tissue in 16 ℃ group increased significantly. However, the activity of glutathione peroxidase (GPX) decreased significantly, but higher than that of the other temperature groups. Compared with other temperature treated groups, the content of malondialdehyde (MDA) decreased significantly. Thus, 16 ℃ temporary culture can not only maintain good water quality, but also reduce the metabolic level of fish and maintain the homeostasis of internal environment, so as to reduce the damage caused by oxidative stress reaction. It is suitable for temporary culture and transportation of Epinephelus fuscoguttatus ♀×E. lanceolatus ♂.
Genetic structure analysis of Ochetobius elongatus between Yangtze River and Pearl River using multiple loci
CHEN Weitao, DUAN Xinbin, GAO Lei, LI Xinhui, YANG Jiping, WANG Dengqiang
 doi: 10.12131/20220007
Taking seven Ochetobius elongatus individuals collected from the Yangtze River during field sampling as samples, we sequenced two mitochondrial genes (Cytb and ND2) and two nuclear genes (mhy6 and RAG2) for the seven samples using Sanger sequencing technique. Combined with the published four gene sequences of 52 O. elongatus samples in the Pearl River, we explored the genetic structure of O. elongatus between the Pearl River and the Yangtze River, so as to provide scientific support for its conservation. We appled phylogenetic analyse, haplotype networks and divergence time estimation in the study. Phylogenetic analyse and haplotype networks reveal that O. elongatus populations in the two rivers generated two deep and independent lineages and formed private alleles at the nuclear gene level. The results suggeste that O. elongatus populations in the two rivers evolved independently without gene flow. The rapid lifting of the Qinghai-Xizang Plateau during the middle Pleistocene might be an important factor that triggered the splitting of O. elongatus populations in the two rivers before 0.38−0.76 million years ago (Ma). Given that strictly geographical division of O. elongatus populations between the two rivers at both mitochondrial and nuclear gene levels, we suggest that these two populations should be regarded as two evolutionary significant units, and targeted strategies should be urgently put forward to manage and protect its resources.
A preliminary study on reproduction and feeding habits of Lutjanus gibbus from Meiji Reef of Nansha
WANG Teng, LIU Yong, LI Chunran, LI Chunhou, TANG Guanglong, XIAO Yayuan, LIN Lin, WU Peng
 doi: 10.12131/20210379
Lutjanus gibbus, a kind of coral reef fish with delicious meat and high economic value, whose spawning aggregation can easily lead to overfishing. Based on 67 individuals of L. gibbus collected by diving fishing in the waters of Mischief Reef in July 2020, we investigated its basic biological characteristics, including sex ratio, sexual maturity body length, egg diameter characteristics, fecundity and feeding habits. The results show that the ratio of female to male of L. gibbus was 2:1; the 50% sexually mature body lengths of males and females were 204.757 and 201.623 mm, respectively; the egg diameter of stage IV gonadal was 0.176–0.419 mm with an average of 0.296 mm; the frequency distribution of egg diameter was unimodal. The fecundity of L. gibbus was 51 858–276 205 eggs with an average of 139 145 eggs. Its fecundity had a significant power function relationship with body length and body mass. The preys of L. gibbus from Meiji Reef were crabs, fish, snails, shellfish and shrimps. The stable isotope study shows that the average trophic level of L. gibbus was 3.33, and its feeding habits changed significantly with individual development (the niche width was narrower and the trophic level was higher).
Effect of trichloroisocyanouracic acid on antibiotic resistance genes in aquaculture water of shrimp
XIA Taotao, SU Haochang, HU Xiaojuan, XU Yu, WEN Guoliang, CAO Yucheng, YU Zhaolong
 doi: 10.12131/20210361
In order to explore the feasibility of removing and controlling the spread of antibiotic resistant genes (ARGs) by the fishing oxidant trichloroisocyanuric acid (C3Cl3N3O3) in the aquaculture water environment, we applied real-time quantitative PCR to monitor and determine the ARGs concentrations in the offshore source water, storage water of sedimentation tank and reserved water after oxidation and disinfection for 29 d. The final concentration of trichloroisocyanuric acid used for oxidation and disinfection was 40 mg·L-1. The target ARGs were commonly found in the aquaculture environments, including sul1, sul2, tetX, tetM, floR, cmlA and qnrA. The results show that sul1, sul2, floR and tetX were the dominant ARGs among the above mentioned water samples. The number of types and total concentration of ARGs were the highest in offshore source water. The total concentrations of ARGs in the storage water of sedimentation tank were lower than those in the offshore source water, especially the concentrations of sul2 and floR were 0.86 log and 0.34 log lower than those in the offshore source water, respectively. After oxidation and disinfection by trichloroisocyanuric acid, the total concentrations of ARGs in the reserved water decreased, and compared with the offshore source water, the concentrations of sul2 and floR decreased by 1.58 log and 1.30 log, respectively. The results indicate that offshore source water is the main source of ARGs in the aquaculture environment. Oxidation and disinfection treatment on offshore source water with trichloroisocyanuric acid can reduce the concentrations of common ARGs in the aquaculture water significantly, which is helpful to prevent and control the spread of ARGs in the aquaculture environments.
Estimation of genetic parameters and its breeding progress for body mass and body length of Cyprinus carpio
DU Xuesong, CHEN Zhong, WEN Luting, PAN Xianhui, HUANG Yin, ZHOU Kangqi, LIN Yong, LI Zhe, LUO Hui, QIN Junqi
 doi: 10.12131/20210353
In order to improve the growth rate of the cultured population of Cyprinus carpio in Quanzhou, two generations of breeding were carried out by family breeding method. The body mass and body length indexes of 3 699 individuals in 121 families of G0, G1 and G2 generations of C. carpio were measured. The heritability, phenotypic correlation and genetic correlation of body mass and body length traits were estimated by mixed linear model. The selection progress of G0 ~ G2 generations was evaluated by the method of breeding value and least square value estimation based on target traits. The results show that the variable coefficient, heritability estimates, correlation value between heredity and phenotype in body mass were 0.50 0.72, 0.132 (P<0.01) and 0.921 (P<0.01), respectively. The variable coefficient, heritability estimates, correlation value between heredity and phenotype in body length was 0.18 0.22, 0.122 (P<0.01) and 0.995 (P<0.01), respectively. The value of selective reaction in body mass estimated by breeding value based on target traits and least square estimation was 12.82% and 15.45%, respectively, while 2.76% and 6.60% in body length, respectively, which indicates that the evenness of body mass was low, and it did not participate in breeding production, but had high breeding and improvement potential. In general, this population of C. carpio obtained effective genetic progress after two successive generations by the family breeding, but with a modest progress. In is suggested that molecular-assisted selection (MAS) and marker-assisted large-scale mixed families' selection should be adopted in the future breeding so as to improve the breeding efficiency.
Effect of carbon dioxide anesthesia on physiology and quality of tilapia
YUAN Yuanyue, CEN Jianwei, LI Laihao, YANG Xianqing, HUANG Hui, WEI Ya, HAO Shuxian, ZHAO Yongqiang, WANG Yueqi, LIN Zhi
 doi: 10.12131/20210276
We used carbon dioxide (CO2) to anesthetize tilapia (Oreochromis niloticus) to reduce the stress response caused by operation, and analyzed the changes of physiology and meat quality of tilapia during anesthesia and resuscitation. By studying the anesthetic effects of different treatment temperatures, we found that the optimal temperature for CO2 anesthesia of tilapia was 15 ℃; the duration of anesthesia was (101±18) s; the duration of resuscitation was (134±23) s. The serum indexes of hydrocortisone (COR), blood glucose (GLU), aspartate aminotransferase (AST),  alanine aminotransferase (ALT) and alkaline phosphatase (ALP) increased significantly after anesthesia, but decreased after resuscitation. The glycogen (GLY) content decreased significantly after anesthesia, while the lactic acid (LD) content in liver reached the maximum value after resuscitation. The LD content in muscle increased during anesthesia but decreased when the stress was relieved. High malondialdehyde (MDA) content but low superoxide dismutase (SOD), glutathione peroxidase (GSH-PX) and total antioxidant capacity (T-AOC)  activity were observed during anesthesia. The hardness, adhesiveness and chewiness of the fillets were significantly affected by anesthesia, but could recover to the control group's level after 24 h, with stable flexibility. In conclusion, tilapia can be anesthetized effectively and quickly after CO2 anesthesia treatment; anesthesia treatment causes oxidative stress response of tilapia; and the physiological state of tilapia can be restored after stress was relieved.
A preliminary study on community structure of mesopelagic fish in cold seep of Xisha Islands
TIAN Han, JIANG Yan'e, ZHANG Jun, CHEN Zuozhi, XU Shannan, ZHU Jiangfeng
 doi: 10.12131/20210370
We used the midwater trawl to investigate the mesopelagic fish resources inside and outside the cold seep in the Xisha Islands. A total of 106 species of mesopelagic fish had been identified which belong to 62 Genera, 31 Families and 12 Orders, with the dominant groups being Myctophiformes and Stomiiformes. Among them, 84 species of fish belonging to 54 Genera, 30 Families, 11 Orders were collected inside the cold seep; while 60 species of fish belonging to 32 Genera, 13 Families and 6 Orders were collected outside the cold seep. There were 38 shared species of mesopelagic fishes belonging to 22 Genera, 9 Families, 5 Orders inside and outside the cold seep, and the main shared species were Chauliodus sloani, Ceratoscopelus warmingii and Diaphus garmani. The Jaccard species similarity index shows that the species similarity of mesopelagic fish was moderately different inside and outside the cold seep (I=35.8%). The average taxonomic distinctness (Δ+) of mesopelagic fish was significantly higher inside the cold seep than that outside (P<0.01), but the variation in the taxonomic distinctness (Λ+) of mesopelagic fish community was inverse (P<0.01). From the perspective of pelagic distribution, there were significant differences in the species composition of the mesopelagic fish communities inside and outside the cold seep (P<0.01). In the surface waters, the mesopelagic fish diversity inside the cold seep was lower than outside, while it’s the opposite in the deeper water layers. There was a correlation between the fish communities at different stations inside and outside the cold seep in terms of water stratigraphy and timing, with higher similarity between the deeper layers inside the cold seep; and higher similarity between the nocturnal surface layers inside the cold seep area and the nocturnal surface layers outside the cold seep. The results show that there are differences in the mesopelagic fish communities inside and outside the cold seep, with more species of mesopelagic fish inside the cold seep and a higher diversity of species in the deeper water layers. Eight key species that distinguish the mesopelagic fish communities in the waters inside and outside the cold seep include Bolinichthys longipes and Vinciguerria nimbara, having a cumulative contribution of 56.06%.
The protective effect of Xiaochaihu Decoction on D-GalN/ LPS-induced hepatocyte injury in hybrid grouper (Epinephelus lanceolatusy♂× Epinephelus fuscoguttatus♀)
ZOU Cuiyun, CHEN Xiaojing, WU Yingxin, HUANG Jinxiong, TAN Xiaohong, HU Xinyue, GAN Songyong, WU Jinhui
 doi: 10.12131/20210362
The present study is aiming at evaluating the protective effect of Xiaochaihu Decoction (XCHD) on chemical hepatocyte injury. Hepatocytes were treated with D-GalN (20 mmol·L–1) and LPS (1 μg·mL–1) for 24 h to build a hybrid grouper (Epinephelus lanceolatus♂×E. fuscoguttatus♀) hepatocyte injury model, pretreated with different concentrations of XCHD (100, 200 and 400 μg·mL–1) (D-GalN/LPS damage), measured hepatocyte viability by the CCK-8 assay. Hepatocyte morphology was visualized by HE staining, and cell supernatants were collected to detect the content of the inflammatory factors INF-, COX-2, and PGE2, as well as the expression of apoptotic and immune-related genes in the cell cryoprecipitate. The results show that XCHD can improve the survival rate of hepatocytes, inhibit INF-γ activity and coX-2 and PGE2 contents in the supernatant of hepatocytes induced by D-GalN/LPS injury to a different extent, reduce LDH, AST and ALT contents and apoptosis rate of hepatocytes, it also has a significant protective effect on the structure of hepatocytes, in the meantime significantly inhibits the up-regulation of apoptosis-related genes caspase-3, caspase-9, and P53, and enhances the up-regulation of immune-related genes TLR3. According to the data from the statistical analysis, the inhibition effect was most obvious in the 200 μg·mL–1 XCHD group. In conclusion, XCHD has a protective effect on the chemical liver injury of tiger dragon hybrid grouper, and can prevent the occurrence and development of liver disease, providing a new insight for the study of liver protection drugs in fish.
Effects of cbpD gene on virulence and related biological characteristics of Vibrio alginolyticus
SU Wenxiao, DENG Yiqin, ZANG Shujun, WANG Qian, LIN Ziyang, FENG Juan
 doi: 10.12131/20220025
In order to study the virulence and related biological characteristics of Vibrio alginolyticus after the absence of Chitin-binding protein D (CbpD) gene, the cbpD gene deletion mutant strain of V. alginolyticus ZJ-T was constructed by the homologous recombination technique. Moreover, the virulence to Danio rerio and other related physiological processes were compared between the wild type strain and the cbpD gene mutant strain, including the growth ability, bacterial colony morphology, motility, extracellular protease secretion activity, hemolytic activity and antibiotic sensitivity, biofilm formation, hydrogen peroxide and copper ion resistance as well as ion absorption capacity. The results show that due to the absence of cbpD gene, the swimming motility, swarming motility and extracellular protease activity all reduced, the resistance to copper ion of the mutant strain strengthened, and its virulence to D. rerio was weakened. However, the deletion of cbpD gene did not affect the growth of the strain in nutrient-rich medium, biofilm formation, hemolytic activity, stress response to H2O2, uptake and utilization of iron and sensitivity to most antibiotics. In conclusion, the results indicate that cbpD may promote the virulence by positively regulating the motility, extracellular protease secretion activity of V. alginolyticus.
Effect of Haematococcus pluvialis on growth performance, antioxidant capacity and immune responses of Lates calcarifer
YU Wei, CHEN Xueqing, YANG Yukai, HUANG Xiaolin, HUANG Zhong, LI Tao, MA Zhenhua, WU Qia'er, YU Gang, ZHOU Chuanpeng, LIN Heizhao
 doi: 10.12131/20220002
To investigate the effects of Haematococcus pluvialis on the growth performance, antioxidant capacity, haematological indexes and immune responses of Lates calcarifer, we had fed L. calcarifer by six diets containing 0 (C), 0.2% (H1), 0.4% (H2), 0.6% (H3), 0.8% (H4) and 1.0% (H5) H. pluvialis for eight weeks. The results show that the specific growth rate (SGR) and weight gain rate (WGR) in H2, H3, H4 and H5 groups were significantly higher than those of the control group (P<0.05). Compared with the control group, the whole-body lipid protein content decreased significantly in the treatment groups (P<0.05). The dietary H. pluvialis improved the total antioxidant capacity (T-AOC) significantly (P<0.05), while the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) activities and malondialdehyde (MDA) content were significantly lower than those of the control group (P<0.05). Compared with the control group, in H3, H4 and H5 groups, the levels of red blood cell (RBC) and hemoglobin (Hb) increased (P<0.05), but the levels of triglyceride (TG), cholesterol (TCHO) and low-density lipoprotein cholesterol (LDL-C) decreased significantly (P<0.05). The complement 4 (C4) and immunoglobulin (Ig) contents and lysozyme (LYZ) activities improved significantly in the treatment groups than in the control group (P<0.05). The regression analysis on the WGR indicates that the recommended optimum dietary H. pluvialis level for the optimal growth of L. calcarifer is 0.66%.
Seasonal variatons of digestive tract index, histology characteristics and enzyme activity of Holothuria edulis
TAN Chunming, ZHAO Wang, MA Zhenhua, YU Gang
 doi: 10.12131/20210356
To reveal the environmental regulation mechanism and aquaculture of tropical sea cucumber, and provide scientific basis for its artificial breeding, we studied the seasonal variations of physiological and biochemical conditions of Holothuria edulis, monitored the changes of the digestive tract index, histology characteristics and enzyme activities of H. edulis. Results show that the feeding state of H. edulis was relatively vigorous in spring and summer, and exhibited similar characteristics to Stichopus japonicus's aestivation in winter, which is characterized by the decline of body mass, the atrophy of digestive tract tissue, the emergence of a large number of cavities due to cell apoptosis, the decrease of the thickness of transverse folds and the decrease of the density of columnar epithelium in the intestinal wall structure. The digestive enzymes and immune enzymes activities of the digestive tract tissues were the highest in March and June, respectively. In December, except for the alkaline phosphatase activity that regulates metabolism, all the others were at low values. Therefore, it is preliminarily judged that H. edulis have hibernation phenomenon.
Responses of important virulence factors of Aeromonas veronii to environmental conditions
WANG Qian, DENG Yiqin, LIN Ziyang, SU Wenxiao, LIU Mengyao, CHENG Changhong, GUO Zhixun, FENG Juan
 doi: 10.12131/20210273
As important pathogenic factors of Aeromonas veronii, flagellin, quorum sensing and Type III secretion system (T3SS) are closely related to their pathogenicity and regulated by varieties of environmental conditions. In order to study the effect of variation in external environmental factors on the pathogenic factors of A. veronii, we used the ascF, fliE and luxR factors of A. veronii as objects by real-time PCR method. The response of ascF, fliE and luxR genes to environmental factors such as temperature, pH, rotating speed and ions were explored at the transcription level. The results show that the three genes of A. veronii had a positive response to acidic environment (pH 6.5−7.0), low and medium speed (150−210 r·min−1), Zn2+ and Mg2+. The response patterns of the three genes of the two strains of A. veronii with different molecular typing were different, indicating that the pathogenic mechanisms of A. veronii might be different. Besides, the important virulence factors of A. veronii were regulated by environmental conditions and showed different regular change. The results can provide reference for further research on the pathogenesis of A. veronii.
Effects of cold stress on black porgy tissue injury and apoptosis gene expression
WEI Mingliang, ZHANG Zhiwei, ZHANG Zhiyong, LIN Zhijie, ZHU Fei, JIA Chaofeng, MENG Qian, XU Dafeng, ZHANG Caojin
 doi: 10.12131/20210372
In order to explore the physiological adaptation mechanism of black porgy (Acanthopagrus schlegelii) under low temperature stress, we designed three temperature gradient groups (15, 10 and 5 ℃). Taking 15 ℃ as the control group and with a low temperature stress for 24 h, we studied the tissue structure changes, physiological, biochemical reactions and the expression of apoptosis genes before and after the cold stress. The results show that with the intensification of low temperature stress, tissue damage such as liver vacuolation, gill lamellae contraction and breakage and muscle fiber breakage were aggravated. The content of triglyceride (TG) in the liver decreased significantly, while the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) as well as the content of total cholesterol (T-CHO) increased significantly, indicating that the black porgy had suffered from liver dysfunction and structural damage under cold stress condition. At 10 ℃, the liver reduced the damage of cold stress by decreasing expression levels of apaf-1, bax and caspase-1 genes, increasing expression of caspase-3 and diablo genes so as to reduce the loss of liver cells. When the temperature reached 5 ℃, the temperature exceeded the black porgy's physiological regulation threshold, so the degree of liver cell damage was aggravated. The expression of apaf-1, bcl-2 and diablo genes were promoted, while the caspase-3 gene expression was inhibited in order to maintain the homeostasis of liver cells to the greatest extent. It is showed that as the temperature decreased, the liver, gills and muscle damages of black porgy increased. The liver regulated the expression of AST, ALT, T-CHO, TG and apoptotic pathway related genes to reduce the damage caused by tissue damage.
Fast determination of prometryn in aquatic products by QuEChERS combined with gas chromatography mass spectrometry
MA Lisha, YIN Yi, TIAN Fei, XIE Wenping, SHAN Qi, ZHENG Guangming, LI Lichun, LIU Shugui, DAI Xiaoxin, ZHAO Cheng, WEI Linting, LIN Jiawei
 doi: 10.12131/20210351
A method was developed for the determination of prometryn in aquatic products by quick,easy, cheap, effective, rugged and safe (QuEChERS) extraction coupled with gas chromatography mass spectrometry. The samples were extracted by acetonitrile-dichloromethane mixture (V:V=8:2) and purified by neutral alumina, zirconium dioxide, PSA and GCB, quantified with internal standard. Good linearity was obtained in the range of 5.00−200 µg·L−1 with the correlation coeficient of 0.9999. The average recoveries were 85.8%−111.8% in Ctenopharyngodon idellus, Siniperca chuatsi, Fenneropenaeus chinensis, Stichopus japonicus and Meretrix meretrix at four spiked levels of 10, 20, 40 and 200 µg·kg−1 with RSDS of 1.2%−8.8%, which meets the quality control specifications required in the national standard (GB/T 27404−2008 Criterion on Quality Control of Laboratories-Chemical Testing of Food). The limits of detection (S/N≥3) and quantification (S/N≥10) were 5.0 and 10.0 µg·kg−1, respectively. The method is suitable for the rapid determination of the prometryn residues in aquatic products owing to its advantages of simplicity, sensitivity, accuracy and better purification.
Preparation of active peptide from Pinctada martensii adductor muscle and evaluation of its auxiliary hypoglycemic effect
LIAO Jin, LIN Haisheng, WU Bin, QIN Xiaoming, CAO Wenhong, GAO Jialong, ZHENG Huina, ZHANG Chaohua, TAN Qiqing
 doi: 10.12131/20210377
To explore the potential nutritional value of shellfish active peptides, we hydrolyzed the adductor muscles of Pinctada martensii, Chlamys nobilis and Atrina pectinate by compound protease and flavor protease, and investigate the effects of protease types, enzymolysis time, pH, temperature and enzyme dosage of the enzymatic hydrolysate on the inhibitory activity on α-glucosidase, so as to screen out the optimal enzymatic hydrolysate and further verify its auxiliary hypoglycemic activity through animal experiments. Results show that the hydrolysate of three kinds of adductor muscle had α-glucosidase inhibitory activity. The enzymatic hydrolysate of Pinctada martensii adductor (EHPA) muscle was most active at enzymolysis time of 3 h, pH of 7.0, enzymolysis temperature of 50 ℃ and enzyme dosage of 5 000 U·g−1. Under these conditions, the inhibitory activity of α-glucosidase was 24.54%, which was related to the short chain polypeptide content. The animal experiments indicate that EHPA had the activity of auxiliary hypoglycemia. In summary, EHPA has potential application value in developing functional food for auxiliary hypoglycemic function.
Molecular characterization and expression of MAP2K1 gene in Hyriopsis cumingii
LIU Meiling, SHANGGUAN Xiaozhao, WANG Xiaoqiang, WANG Yayu, WANG Guiling, LI Jiale
 doi: 10.12131/20210328
In order to study the role of the MAP2K1 (MEK1) gene in the sex determination of Hyriopsis cumingii, we applied RACE method to clone the MAP2K1 gene sequence. We used real-time fluorescence quantitative analysis to compare MAP2K1 gene in six tissues (gonads, adductor muscle, hepatopancreas, gills, mantle, foot), gonads at early developmental stage (1−8 month old) and 1−3 years' level of expression in male and female glands of H. cumingii. We determined the location of MAP2K1 gene in the gonads of 2-year-old H.cumingii by in situ hybridization. The results show that the ORF region of MAP2K1 gene was 1 194 bp in length and encoded 397 amino acids. MAP2K1 gene was highly expressed in the ovary; the expression level was the highest at 2 months of age at early development stage; the expression results from 1−3 years of age show that the expression of MAP2K1 gene in the ovary was higher than that in the spermatozoa for the same period (P<0.05). The in situ hybridization results show that the MAP2K1 gene had a significant hybridization signal in the oocytes and eggs of female H. cumingii. RNAi results show that the expression of the downstream gene MAP2K1 gene decreased by 82.31% in females and 73.60% in males after interfering with the upstream gene C-MOS gene of MAP2K1 gene. In conclusion, MAP2K1 gene may be involved in the ovarian development process and is a female-biased gene in H. cumingii, and C-MOS gene affects its expression.
Mining of InDel marker and association analysis of hypoxia tolerance traits in Trachinotus ovatus based on resequencing
SAN Lize, LIU Baosuo, ZHANG Nan, GUO Liang, GUO Huayang, ZHU Kecheng, ZHANG Dianchang
 doi: 10.12131/20210347
In this study, the whole genome re-sequencing technology was applied to analyze the InDel differences of Trachinotus ovatus gene and the significant correlation between hypoxia tolerance traits. The InDel sites were excavated, and the candidate genes related to hypoxia tolerance traits were discussed. Altogether 693.48 Gb was obtained by sequencing, and the average value of Q30 was 90.8%. A total of 2 574 178 InDel markers were found by annotation analysis. A total of 249 395 InDel markers were found in the 50 T. ovatus in the tolerance group, of which 2 209 were located on exons. It is found that there were mutated genes in the nucleotide excise repair signaling pathway and cell adhesion molecules. Three InDel markers (InDel 22883061, InDel 24919481 and InDel 14451779) were found to be close to the significance threshold by association analysis between InDel markers and hypoxia tolerance trait. Nine candidate genes were obtained by annotation analysis. The selected InDel markers were of great value for selecting and identifying molecular marker selection breeding. The annotated candidate genes provide basis and reference for the study of the hypoxia tolerance mechanism of T. ovatus.
Optimization on calculation method of horizontal illuminance for metal halide fish lamp around fishing boats
WANG Weijie, WAN Rong, KONG Xianghong, XIAO Yuchen
 doi: 10.12131/20210320
Monte Carlo simulation is an effective numerical simulation approach to calculate illuminance at target region by discretizing beam into photons and calculating illuminance based on tracking photon path. In order to calculate the horizontal illumination distribution of the fish lamp accurately, taking the metal halide fish lamp as an example, we analyzed and optimized the photon number and photon emission model within Monte Carlo (MC) simulation. For the photon number, we carried out numerical simulation by setting different photon numbers to analyze its influence on the stability of simulation results. Meanwhile, we presented a photon emission optimization model based on the luminosity distribution data of fish lamp and verified by the measured data. The results show that: 1) The larger the number of the simulated photon, the better the stability of the simulation result. Taking the calculation point with a horizontal distance of 5m from the lamp as an example, when the value exceeded 108, the coefficient variance (CV) was 0.07% and when the value exceeded 1010, the CV was 0.05%. 2) By using the optimization model, the mean relative error (MRE) between the simulated and measured data reduced from 0.051 2 to 0.045 3. In addition, the light field illumination of fishing boats in the actual working environment was calculated by using the optimization model. The average error between the calculated value and measured value was about 0.052 3.
Evaluation of scale effect on hydrodynamic force of V-shaped otter board based on CFD
LIU Jingbin, TANG Hao, XU Liuxiong, SUN Qiuyang, LIU Wei, YIN Liqiang, ZHANG Feng
 doi: 10.12131/20210355
The main way to study the hydrodynamic characteristics of the otter board is to build a physical model to measure its hydrodynamic characteristics based on the similarity law. In this study, we analyzed the lift, drag coefficient and flow field distribution of V-type otter board with three scale ratios (1∶2, 1∶3 and 1∶4) and three thickness (2, 5 and 10 mm), and compared them with the corresponding model test results to explore the influence of different physical model scales on hydrodynamic estimation of the otter boards. The results show that: 1) With the increase of the angle of attack, the drag coefficient of otter board with all scales gradually increased, while the lift coefficient first increased and then decreased, and the lift-drag ratio gradually decreased. 2) When the angle of attack reached 30°, the apparent separation vortex appeared at the back of the otter board, resulting in the decrease of simulated lift force. 3) With the increase of the otter board model scale, the separation effect of the boundary layer on the otter board surface and the separation vortex of the flow field in the wake area gradually increased, and the lift, drag and lift-drag ratio of the otter board also showed an increasing tendency. The thickness of the mesh plate had little effect on the flow field, lift and resistance, and the average error of the maximum lift coefficient relative to the model test is 4.97%. As the model scale increased, the prediction error of hydrodynamic force decreases gradually.
Hydrodynamic performance of Argentine shortfin squid (Illex argentinus) bottom trawl based on model experiment
HAO Yuxin, WAN Rong, ZHOU Cheng, YE Xuchang, GUAN Qinglong, ZHANG Xiaoxian
 doi: 10.12131/20210343
Illex argentinus, inhabiting in shallow waters with a short life cycle, is an important economic cephalopod in the high seas fishing ground of the southwest Atlantic Ocean. Squid jigging and bottom trawling are the main fishing patterns to catch this species. However, there are some problems in the bottom trawling, such as high energy consumption, poor matching between vessel and trawl. Thus, it is necessary to understand the hydrodynamic performance of bottom trawl for I. argentinus. In this paper, we conducted a model experiment in the dynamic water tank to explore the effects of towing speed, horizontal spreading ratio, buoyancy-mass ratio on hydrodynamic performance of height of net opening, resistance, coefficient of energy consumption and power consumption. The model net was designed based on the small mesh six-panel single boat bottom trawl used for the main capture of I. argentinus [main scale: 200 m×113.8 m (84.6 m)]. According to the Tauti's Law, the model experiment was scaled with the large scale ratio of 1:30 and the small scale ratio of 1:5. When the towing speed V was 3 kn and the horizontal spreading ratio L/S was 0.54, the buoyancy-mass ratio increased from 0.6 to 0.7, the height of the net opening increased from 9.66 m to 14.1 m, and the resistance increased from 73.73 kN to 83.48 kN. However, with the increase of towing speed, the influence of the buoyancy-mass ratio on the height of the net opening and resistance decreased. When the sweeping area of trawl opening was less than 200 m2, the energy consumption coefficient was greatly affected by the horizontal expansion ratio, on the contrary, it was greatly affected by the height of trawl opening. The power consumption increased with towing speed and horizontal spreading ratio. It accounted for more than 10% of main engine power for vessel when towing speed was more than 4 kn.
Effects of salinity stress on oxygen consumption rate, ammonia excretion rate and immune-related enzyme activities of Strombus luhuanus
CHEN Xu, ZHAO Wang, CHEN Mingqiang, TAN Chunming, YU Gang
 doi: 10.12131/20210346
To investigate the adaptability of salinity stress of Strombus luhuanus, we determined the oxygen consumption rate and ammonia excretion rate of S. luhuanus at different salinity levels of 17, 22, 27, 32 (control group) and 37. Then we set groups with the same salinity levels to investigate the effects of immune-related enzyme activities. The results indicate that the oxygen consumption rate and ammonia excretion rate in control group were significantly higher than the other groups (P<0.05). the results show that the activity of total superoxide dismutase revealed insignificant difference (P>0.05). Compared with the control group, the catalase activity of hepatopancreas groups increased to varying degrees, while the catalase activity of muscle groups was not significantly different (P>0.05). The peroxidase activities of hepatopancreas in the control group, salinity 27 and 37 groups were significantly higher than those in salinity 17 and 22 groups (P<0.05). The peroxidase activities of muscle in the experimental groups were significantly higher than that in the control group (P<0.05). The lysozyme activities of hepatopancreas and muscle in the control group were significantly higher than those in the other experimental groups (P<0.05). In summary, the oxygen consumption rate, ammonia excretion rate and activities of immune-related enzyme have significant effects on S. luhuanus under salinity stress.
Evaluation of fisheries ecological environment in adjacent sea areas of Wanshan Archipelago in Pearl River Estuary in spring
WU Peng, LIU Yong, XIAO Yayuan, XIE Yufang, TANG Guanglong, LIN Lin, WANG Teng, LI Chunhou
 doi: 10.12131/20210332
Wanshan Archipelago plays an important role in the conservation of fishery resources in the Pearl River Estuary. However, there is still a lack of sufficient research on the fishery ecological status of the adjacent waters of islands and reefs in this region. Thus, we analyzed the characteristics of the seawater environment and zooplankton community in Wanshan Archipelago in April 2021. The results show that the seawater environment of Wanshan Archipelago was greatly influenced by fresh water input from the Pearl River coastal channels. Consequently, the concentration of dissolved inorganic nitrogen, nutrient quality index and eutrophication index were higher in the adjacent sea areas of Guishan Island and Dong'ao Island which are located in the northwestern Wanshan Archipelago. Eutrophication was observed in this area. Furthermore, the primary production in the seawater of these two islands was also higher, most with medium and low levels. The zooplankton communities of Wanshan Archipelago can be divided into three groups, and one of them affiliated to the adjacent sea areas of Guishan Island had a low Shannon index value, indicating a potentially polluted seawater environment. However, high abundances of spawning and larval fish were observed at Guishan Island (133 and 18 egg·m−3, respectively), suggesting that it is an important fish spawning area. The primary production and Pielou evenness index of zooplankton can reflect the correlation between water environment and zooplankton community in Wanshan Archipelago, and can indicate the state of water eutrophication.
Effects of elevated CO2 and photoperiod on growth and physiological performance inseedlings of Ulva prolifera
ZHOU Wei, WU Hui, HUANG Jingjing, ZHAO Xixing, WANG Jingwen, WANG Jinguo
 doi: 10.12131/20210278
Ulva prolifera seedlings, which are the main component of the natural "seed bank" of green tide algae, play an important role in the occurrence and development of green tide. In this study, both the growth and physiological responses of seedlings were studied after the seedlings being cultured at two different CO2 levels (LC, 400 μatm; HC, 1 000 μatm) in combination with three different photoperiods (LL: 10 L:14 D; ML: 12 L:12 D; HL: 14 L:10 D). Therelative growth rate of seedlings were significantly enhanced by elevated CO2 under three light-dark regimes. The seedlings showed an obvious higher growth rate and lower dark respiration rate (Rd) at HL treatment than at ML treatment, regardless of the CO2 treatment. The photochemical performance was largely unaffected by elevated CO2 and day length. Elevated CO2 had negative effects on chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoids (Car) content, longer day length also inhibited the synthesis of these pigments. These results suggest that the growth and physiological of seedlings are significantly influenced by elevated CO2 and photoperiod. HCHL promotes the growth of its seedlings and increases the possibility of outbreak of green tide caused by U. prolifera. This study provides basic data for in-depth understanding of the causes of green tide algae outbreak.
Site selection of marine ranching in Wailingding Island sea area of Zhuhai
XIE Xiaoyan, CHEN Pimao, TONG Fei, YUAN Huarong, FENG Xue, YU Jing, YU Jie, SHU Liming
 doi: 10.12131/20210241
Site selection of marine ranching plays a key role in the construction of marine ranching. Appropriate location is the precondition of a successful marine ranching construction. In this study, we selected 34 indicators as factors for marine ranching suitability evaluation (Coastline stability, marine functional zoning, marine ecological red lines, aquaculture water tidal flat planning, marine engineering and facilities), and established an index system of marine ranching location. On this basis, according to the actual situation of Wailingding Island of Zhuhai, we selected eight indexes including length and area change intensity of island coastline, marine functional zoning, marine ecological red line, beach planning of aquaculture waters, ports, anchorages, navigable areas and submarine pipelines, to evaluate the suitability of marine ranching site selection in that sea area by using the spatial analysis method of GIS. The results show that there was no most suitable and more suitable area for marine ranching construction, and the areas of generally suitable and unsuitable areas for marine pasture construction were 33.09 and 45.59 km2, respectively. The suitable area for marine ranching construction was similar to the existing artificial reefs and planned marine ranching areas in Zhuhai.
Advances on antibiotic resistance genes (ARGs) in aquaculture environment
LI Danyi, WANG Xunuo, ZHANG guangju, WANG Zenghuan, HUANG Ke
 doi: 10.12131/20210207
Antibiotics play a significant role in the disease control of aquatic organisms and output increase of aquatic products. However, the long-term abuse of antibiotics can result in the occurrence of antibiotic resistant bacteria (ARB) which harbor antibiotics resistance genes (ARGs) in aquatic organisms. The persistent existence, migration and spread of ARGs in aquaculture environment will potentially cause genetic pollution, destroy the ecological balance, and pose risks to human health. Therefore, how to constrain the spread of antibiotic resistance has attracted global attention. In terms of the research advancement of ARGs in aquaculture environment, this review systematically summarizes the status of ARGs pollution coupled with the source, migration and spread behavior of ARGs and their influencing factors, illustrates the correlations between ARGs and antibiotics, microbial communities and environmental factors, as well as discusses the effect of antibiotics, ARGs and ARB on ecological environment and human health. On this basis, it overviews the management strategies and removal technologies of ARGs, and proposes the future research directions regarding ARGs. The review aims to provide reference in revealing the pollution mechanism of ARGs and reducing the transmission risk of antibiotic resistance.
Pattern of fish community and its relationship with environmental factors in Fangchenggang (Qinzhou coastal area of Beibu Gulf)
ZHANG Gongjun, YANG Changping, LIU Yan, ZHOU Wenli, SHAN Binbin, WANG Liangming, WANG Sihan, SUN Dianrong
 doi: 10.12131/20210255
We analyzed the fish assemblage composition and spatio-temporal distribution of fish stocks based on the bottom trawl survey data in Fangchenggang (Qinzhou coastal area of Beibu Gulf) in 2016. Combining with the information of temperature, salinity, dissolved oxygen, pH and depth, we investigated the relationship between fish community structure and environmental factors. A total of 152 fish species belonging to 15 orders, 55 families, and 96 genera had been collected, and Parargyrops edita, Secutor Ruconius, Saurida tumbil and Sebastiscus marmoratus were the dominant species. The abundance of fish stocks was the highest in spring. The diversity index was higher in spring and summer, but lower in winter. Four distinct groups were defined by Cluster and non-metric multidimensional scaling (NMDS) analysis, and the average similarity of the groups ranged from 18.27% (Group I) to 32.49% (Group II). The analysis of similarity (ANOSIM) shows that the differences of fish composition among different groups were extremely significant (R=0.703−0.982, P<0.01), with the most sinificant difference of 98.02% between Group I and IV. The results of redundancy analysis (RDA) show that the temperature of bottom, dissolved oxygen, depth and salinity of bottom were the main environmental factors that affected fish distribution in Fangchenggang.
Optimization of flow field in dual-drain square aquaculture tank with relative arc to width ratio
ZHANG Qian, GUI Jinsong, REN Xiaozhong, XUE Boru, BI Chunwei, LIU Ying
 doi: 10.12131/20210044
In order to improve the flow field characteristics in dual-drain square aquaculture tank, we combined arc angle and straight edge to optimize the flow field, so as to provide better aquaculture equipment for the recirculating aquaculture industry. We applied computational fluid dynamics technology to simulate the flow field in dual-drain aquaculture tanks, and evaluated the effect of relative arc to width ratio (R/B, R is the radius of arc angle, B is the side length of tank wall) on the flow field characteristics in the tanks by analyzing corrected velocity v0 and uniformity coefficient UC50. The results show a same rule under different conditions of underflow split ratio (The percentage of outflow from the center outlet at the bottom of the tank in the total outflow). The average velocity in the square arc angle aquaculture tanks with 0.2≤R/B<0.4 was about twice than that in the square aquaculture tanks for the same water exchange rate, and there was no significant difference compared with the circular aquaculture tanks. According to the analysis of flow field uniformity, the square arc angle aquaculture tanks with 0.2≤R/B<0.4 had higher uniformity coefficient, and even higher than that of circular aquaculture tanks. The research indicates that the area of lower velocity caused by the right angle in the square aquaculture tanks reduced effectively by the arc angle in the square arc angle aquaculture tanks, and higher space utilization rate was retained. The advantages of the square aquaculture tank and the circular aquaculture tank are fully combined in the square arc angle aquaculture tank, which solves the problem of poor flow pattern in dual-drain square aquaculture tank, with good industrial popularization and application value.