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doi: 10.12131/20210014
[Abstract](36) [FullText HTML](5) [PDF 1461KB](4)
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Skipjack tuna (Katsuwonus pelamis) is widely distributed in the Western and Central Pacific Ocean, and El Niño events have significant impacts on its distribution. Based on the logbook data from mainland of China and the oceanographic environmental data, we applied the Maximum Entropy Model (MaxEnt) to explore the spatial distribution of fishing grounds and the response characteristics of environmental factors in different types of El Niño events. The results show that: 1) The MaxEnt model could predict the distribution of fishing grounds well. 2) The moderate Central Pacific El Niño events were mainly distributed around 160°E in the equatorial Pacific, while the super Eastern Pacific and weak Central Pacific El Niño events were mainly distributed around 170°E. 3) Sea surface temperature (SST), sea temperature at depth of 50 m (T50) and sea surface salinity (SSS) were the key factors affecting the distribution of skipjack tuna. In the moderate Central Pacific El Niño events, SSS had the highest contribution rate, while in the super Eastern Pacific and weak Central Pacific El Niño events, T50 did. 4) The center of gravity of fishing ground along the longitude was mainly distributed between 160°E and 175°W, and the suitable habitat average percentage was different in different El Niño events. The moderate Central Pacific El Niño events was 24%; the super Eastern Pacific El Niño events was 28%; the weak Central Pacific El Niño events was 29%.
doi: 10.12131/20200247
[Abstract](44) [FullText HTML](6) [PDF 688KB](1)
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Thermal processing is a traditional food processing technology, and hot boiling is one of the important methods. After being boiled, the fish tissue will become fragile and the structure will be loose, which is bad for the edible quality of the fish. This paper summarizes the research progress on the effect of hot cooking on the texture of fish meat in recent years, deeply analyzes the mechanism of the texture change, and combines the principle of texture change expounds the methods of maintaining the texture of fish meat by improving protein thermal stability, muscle water retention and muscle gel properties. Then it puts forward the research direction of combining new food processing technology with traditional processing methods to improve the boiling resistance of fish meat in the future, so as to provide reference for the texture preservation technology and edible quality control of fish during hot boiling.
doi: 10.12131/20210023
[Abstract](81) [FullText HTML](16) [PDF 1180KB](10)
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In order to explore the selection and utilization of Chinese seabass (Lateolabrax maculatus) in different subhabitats of the salt marsh of the Yangtze River Estuary, we investigated three subhabitats of tidal creek, mudflat and Scirpus mariqueter vegetation area, and took samples in spring, summer, autumn and winter. The results show that L. maculatus was the dominant species in that area. The spatial niche breadth of L. maculatus decreased gradually in spring, summer and autumn, while the temporal niche breadth was in a descending order of tidal creek>S. mariqueter vegetation area>mudflat. There was a significant spatial-temporal difference in the population distribution of L. maculatus (highest in spring but lowest in autumn; most in tidal creek, followed by S. mariqueter vegetation area and mudflat). The majority of L. maculatus entering the Yangtze River Estuary were juveniles, which occurred mainly in spring. Small-size individuals preferred to inhabit in tidal creek, while large-size individuals preferred to inhabit in mudflat and S. mariqueter vegetation area. For the average feeding grade of L. maculatus, it increased gradually from spring to winter in tidal creek, and increased gradually from spring to autumn but decreased sharply in winter in mudflat, reaching the maximum in summer and decreased gradually in autumn and winter in S. mariqueter vegetation area. In spring, summer and autumn, the average feeding order of L. maculatus was in a descending order of S. mariqueter>tidal creek>mudflat. However, the average feeding grade was in a descending order of tidal creek>S. mariqueter> mudflat in winter.
doi: 10.12131/20200231
[Abstract](61) [FullText HTML](7) [PDF 1083KB](6)
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To explore the feasibility of using fishery oxidants to eliminate antibiotic resistant genes (ARGs) in aquaculture water and to control their spread, we studied the effects on ARG removal of three commonly used fishery oxidants (Sodium hypochlorite, dibromohydantoin and potassium permanganate) in water source and pond water by real-time fluorescent quantitative PCR. Results show that the concentration of sul1 gene was high in the water source and pond water (105 and 106 copies·mL−1, respectively), and the intracellular sul1 gene was the predominant form. Additionally, sodium hypochlorite had a strong effect on sul1 gene removal in all the experimental groups, and dibromohydantoin only showed a strong removal effect on sul1 gene in the water source. Potassium permanganate only showed a strong effect on the removal of extracellular sul1 gene in both water source and pond water. The results indicate that sodium hypochlorite has the best effect on ARG removal in both water source and pond water for these three common used fishery oxidants. Scientific application of sodium hypochlorite is beneficial to ARG removal and prevention in aquaticulture water.
doi: 10.12131/20200230
[Abstract](62) [FullText HTML](12) [PDF 974KB](6)
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Sudden death occurred in Micropterus salmoides larvae reared on a farm in Foshan, Guangdong Province of China in spring of 2020. To investigate the etiology of this disease, we isolated a strain of bacteria GZXR2020 from the liver tissue of diseased M. salmoides larvae and conducted its molecular identification. We obtained the full-length sequences of the 16S rRNA gene and gyrB gene of the strain by PCR amplification. BLAST results show that the sequences were highly homologous to the corresponding sequence of Aeromonas veronii in GenBank, with homology higher than 99.5% and 98.3%, respectively. Using VITEK2 automatic bacterial identification system and according to the results of a total of 45 physical and chemical identification, sheep blood agar plate hemolysis test that showed β-hemolysis, detection of the virulence genes as well as the physicochemical identification, we identified the bacteria as A. veronii bv. sobria. In the artificial regression infection experiment, intraperitoneal injection of 3×107, 1.5×108 and 3×108 CFU·mL−1 resulted in 7%, 40% and 100% mortality, respectively. The drug sensitivity test of a total of 17 antimicrobial agents shows that the strain GZXR2020 was highly sensitive to 7 antibacterial drugs such as spectinomycin, fleroxacin, florfenicol and so on.
doi: 10.12131/20200183
[Abstract](133) [FullText HTML](18) [PDF 603KB](11)
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Filter-feeding bivalves is one of the most productive species in the world. Large scale aquaculture has greatly increased the number of shellfish in coastal waters. The influences of bivalves' physiological processes and aquaculture activities on the marine ecosystem have drawn lots of attention from scientists. This paper summarizes the current research progress on the impact of shellfish on plankton, and conclude that the influences of bivalves aquaculture on plankton communities in farming areas and its adjacent area include: the filter feeding leads to a grazing pressure and exerts a ‘top-down’ control of planktonic communities in farming areas, resulting in a significant depletion of plankton concentration; selective predation changed plankton community structure; the excretion of shellfish increased the nutrient elements in the water and promoted the growth of phytoplankton; the biodeposition process lead to a deposition and burial of silicon (Si) which resulted in a change in biogenic elements ratio and a limit of diatom; the rearing infrastructures decreased the hydrodynamic and water flow velocity, and prolonged the residence time of plankton inside farming areas, which tends to increase the risk of predation of planktonic populations, reducing biomass and production; bivalves can increase the amount of fouling organisms and have an impact on plankton. Finally, the paper summarizes the scientific problems to be further studied.
doi: 10.12131/20200237
[Abstract](50) [FullText HTML](13) [PDF 925KB](3)
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The first generation (G1) of Chinese mitten crab (Eriocheir sinensis) named "Changdang Lake 1" Strain A (body mass of female parent is more than 200 g) and B (body mass of female parent is more than 250 g) have been obtained. In previous study, G1 showed better growth and culture performance in juvenile crab culture stage, but the performance of adult crab culture is still unclear. Therefore, the difference of growth, survival rate, yield, average mass and size distribution were systematically compared among Strain A, Strain B and unselected groups. The results show that: 1) In middle and later stages of culture (September−November), the average body mass of two breeding groups was slightly higher than that of the control group, and that of Strain B female was significantly higher than that of the control group (P<0.05). In addition, the weight gain rate and specific growth rate (SGR) of Strain B were significantly higher than those of Strain A from May to July (P<0.05). 2) The puberty molting rate and hepatosomatic index of male in the two selected groups were slightly lower than those in the control group. The hepatopancreatic index of Strain B was significantly lower and higher than those of the other two groups on October 20 and November 15, respecitively. 3) The proportion of large-sized crabs (male≥195g, female≥120 g) in male and female of two breeding groups was higher than that of the control group, among which only G1 male of Strain B (195−219.9 g) was significantly higher than that of the control group (P<0.05). Besides, the final average body mass, survival rate, yield and feed conversion rate of the two selected strains were higher than those of the control group. Above all, "Changdang Lake 1" strain A is characterized by high survival rate, yield and feed conversion rate, while Strain B is characterized by high proportion in large-size and great final average body mass.
doi: 10.12131/20200243
[Abstract](55) [FullText HTML](10) [PDF 1038KB](9)
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We studied the effects of different feeding frequencies on the food intake, growth, digestive enzymes, antioxidant enzymes and intestinal tissue of Paralichthys olivaceus under the condition of running water culture, in order to explore the optimal feeding frequency of P. olivaceus. The experiment set up three feeding frequency treatment groups, feeding 2 (T2), 3 (T3), 4 (T4) times per day, lasting 60 d. The results show that the daily intake of T3 group was significantly higher than those of T2 and T4 groups (P<0.05), and there was no significant difference in the specific growth rate and survival rate of T2 and T3 groups, which were significantly higher than that of T4 group (Specific growth rate: P<0.05, survival rate: P<0.01). There was significant difference in the weight gain rate among the three groups (P<0.05); there was no significant difference in the hydrogen peroxide enzymes, total superoxide dismutase and lipase between T2 and T3 groups, which were significantly higher than in T4 group (hydrogen peroxide enzyme, lipase: P<0.01; total superoxide dismutase: P<0.05). There was significant difference in gastric proteases among the three groups (P<0.05), with a descending order of T3, T2 and T4. The intestinal wall thickness, longitudinal muscular thickness and number of goblet cell in T4 group were significantly lower than those in T2 and T3 groups (P<0.01), but there was no significant difference between the T2 and T3 groups, and the thickness of the endocrine cells in T3 group was significantly higher than that of the other two groups (P<0.05), and the difference between the T2 and T4 groups was not significant. Combining the results with the actual situation of breeding, under the condition of running water culture, the most suitable feeding frequency in the process of P. olivaceus cultivation is 3 times per day.
doi: 10.12131/20200260
[Abstract](67) [FullText HTML](37) [PDF 819KB](8)
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In order to use copper sulfate scientifically to treat the disease caused by parasite Amyloodinium ocellatum in farmed fish, golden pompano (Trachinotus ovatus) was used as an animal model to study the copper sulfate's effective concentration and time of killing of each stage of A. ocellatum. The safety concentration of copper sulfate to juvenile golden pompano was evaluated. Results show that the juveniles had good tolerance to copper sulfate and the safety concentration was less than 43.06 mg·L−1. The effective concentrations of copper sulfate to kill full dinospores within 10, 30 and 60 min were 3.13, 0.78 and 0.20 mg·L−1, respectively. At copper sulfate concentrations of 2, 1 and 0.5 mg·L−1, trophonts were detached from the host within 2, 4 and 8 h, respectively. However, tomonts were highly resistant to copper sulfate because they divided when being incubated with 100 mg·L−1 copper sulfate solution. Additionally, the relative protection rates of pompanos infected with A. ocellatum were 80% and 90% when being immersed continuously in 0.2 and 0.4 mg·L−1 copper sulfate solutions respectively for 10 d. These results imply that the immersion to copper sulfate solution can protect golden pompano from A. ocellatum infection at low concentration.
doi: 10.12131/20200251
[Abstract](85) [FullText HTML](8) [PDF 907KB](8)
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To explore the ameliorative effect of Chlamys nobilis and its enzymatic hydrolysates on male sexual function, we investigated the sexual behaviors, organ coefficient, level of serum sex hormone, NO contents and enzyme activity of NOS in penile tissue of the hemi-castrated male SD rats. The results show that C. nobilis and its enzymatic hydrolysates could increase the sexual behaviors of hemi-castrated male rats, such as catching frequency (P<0.05) and mount frequency (P<0.05); decrease the errection latency significantly (P<0.01); and increase the coefficients of testicular and prostate-seminal gland in hemi-castrated male rats significantly (P<0.05). Besides, it could increase the serum testosterone content, stable the levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH). Moreover, it could mediate the production of NO and NOS in penile tissue significantly (P<0.05). Therefore, C. nobilis and its enzymatic hydrolysates can improve the reproductive capacity of hemi-castrated male rats, and the improvement mechanism is probably related to the regulation of serum sex hormones and the promotion of signal factors of penile tissue in hemi-castrated male rats.
doi: 10.12131/20200240
[Abstract](65) [FullText HTML](12) [PDF 1017KB](3)
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With X-ray and ecological digestion methods, the axial skeleton of Seriola dumerili were digested, photographed and described statistically. It is showed that the axial skeleton of S. dumerili included skull and spine. The skull was divided into neurocranium and splanchnocranium. The neurocranium was composed of ethmoidal region, orbital region, otic region, occipital region and circumorbital series. The splanchnocranium was divided into mandibular arch, hyoid arch, branchial arch and opercular series. The supporting structure spine was composed of vertebrae connected front and back. All vertebra consisted of centrum, neural spine and neural arch in different shapes. Partial vertebrae differentiated into parapophysis, ribs, haemal arches and haemal spines. The results show that the main bones of skull were about 128, including 39 neurocranium and 89 splanchnocranium. The number of vertebrae of S. dumerili spine was 24, with 23 neural spine, 23 neural arch, 14 haemal spines, 15 haemal arch, 10 pairs of parapophysis and 9 pairs of ventral ribs, but without dorsal rib.
doi: 10.12131/20210004
[Abstract](85) [FullText HTML](14) [PDF 1061KB](9)
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The in-pond raceway system (IPRS) based on intensive production of ponds is an emerging aquaculture model. In order to further understand the ecological structure dynamics of this system's water body circulation process and to reveal the change characteristics of water quality in purification area, we studied the spatial variability of phytoplankton community structure and the relationship between the phytoplankton community structure changes and the environmental factors by Redundancy Analysis (RDA) during the growing season in IPRS of grass carp (Ctenopharyngodon idella). The system identified 99 species of phytoplankton in seven phyla, mainly including Cyanophyta, Chlorophyte, Bacillariophyta, Euglenophyta, Cryptophyta, Pyrrophyta and Chrysophyta. Chlorophyta had the largest number of species (54 species), followed by Cyanophyta (18 species). In this system, the phytoplankton community structure in different areas was different. The density and biomass of phytoplankton in the middle of the purification area were the highest, and those of Cyanophyta in the purification area were higer than that in the culture area. The relative density of Cyanophyta in different areas was much higher than those of Chlorophyta and Bacillariophyta. From the front to the back of the purification zone, the relative density of Cyanophyta gradually increased, while those of Chlorophyta and Bacillariophyta gradually decreased. The results of RDA show that the main environmental factors that affect the changes in the phytoplankton community structure in the system are temperature, nitrogen and phosphorus nutrients.
doi: 10.12131/20200234
[Abstract](61) [FullText HTML](8) [PDF 785KB](16)
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The stable isotope ratios (δ13C and δ15N) of carbon and nitrogen of Tachypleus tridentatus collected from Beibu Gulf and its potential food source species (Shrimps, crabs, bivalves and fishes) in food web were determined. Besides, their food composition and nutritional position were anayzed by stable isoelement mixture model (SIAR). The results show that the average δ13C and δ15N values of the T. tridentatus were (−17.11±0.03)‰ and (12.14±0.20)‰, respectively. Potential food sources of T. tridentatus were shrimps, crabs, bivalves and fishes. The SIAR model shows that bivalves were the main food source of T. tridentatus with average contribution rate of 31.27% (Fishes: 25.91%, crabs: 23.50%, shrimps: 19.32%). The trophic position of T. tridentatus was 2.02±0.06, while those of fishes, shrimps and crabs were 2.13±0.51, 2.36±0.09 and 2.61±0.21, respectively. Trophic position analysis shows that T. tridentatus is in a relatively weak position in the natural ecosystem food web, and scientific protection measures are urgently needed as it is already endangered.
doi: 10.12131/20200227
[Abstract](49) [FullText HTML](8) [PDF 1144KB](4)
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Stable isotope analysis technology has become an important means in the study of nutrition sources in ecology, but the premise is to obtain the data of stable isotope enrichment effect of animals in different diets. In this experiment, Acentrogobius caninus, Callionymus richardsoni, Metapenaeopsis barbata, Ruditapes philippinarum, Perinereis nuntia and cultured P. aibuhitensis were collected from mangroves and adjacent beaches and used as baits to feed Scylla paramamosain for 66 d. The results indicate that R. philippinarum, P. aibuhitensis and M. barbata had better culture effects on S. paramamosain. The stable isotope abundances of δ13C and δ15N in six natural diets were obviously higher than that in initial crabs. Compared with the initial crabs, the contents of stable isotope δ13C and δ15N of final crabs increased significantly. The enrichment effects of the 13C (∆13C) were 0.7, −0.19, 0.22, 2.58, −0.12 and 2.75 for the six diets, respectively, while the ∆15N varied from −2.98 to 0.21. Most of these values were inconsistent with the judgment baselines (discrimination) of direct predator and prey, which were 0‰−1‰ for ∆13C and 3‰−4‰ for ∆15N, respectively. This may be due to the huge difference of stable isotope enrichment between beach dwelling organisms and land organisms. It is also possible that low water temperature, slow growth and low weight gain rate of S. paramamosain at later stage of the experiment lead to insufficient renewal of carbon and nitrogen in the body.
doi: 10.12131/20200265
[Abstract](65) [FullText HTML](13) [PDF 1031KB](13)
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To study the influence of morphological characteristics of Changfeng silver carp (Hypophthalmichthys molitrix) on its growth, we applied the principal component analysis and path analysis methods to analyze the conventional morphological measurements and truss network. The results show that the correlation coefficients between the morphological traits and body mass were extremely significant at different ages (P<0.01). Besides, the correlation coefficients between them were also different at different stages. Principal component analysis revealed that 6- and 12-month old H. molitrix showed a synergistic growth, as well as development of the overall structure, but it was mainly the growth of the trunk at 36-month age. Path analysis shows that the path coefficients of three morphological traits (x8, x11, x13) for the body mass were significant at three stages (P<0.05), and these traits had significant impacts on the body mass at all stages. The optimal regression equations of morphological traits to body mass were established for the three groups. The effects of morphological traits on the body mass were distinct at different stages. The results suggest that the total length, body length and body height should be selected as breeding targets for H. molitrix at early growth stage. However, the target trait for selective breeding of adult fish should mainly be total length, and the synergistic breeding of fish body width should be emphasized.
doi: 10.12131/20200198
[Abstract](65) [FullText HTML](8) [PDF 873KB](8)
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Based on the stratified survey data of larvae and juveniles in the adjacent waters of the Yangtze River Estuary in spring 2016, we investigated the stratified variation characteristics of species number, abundance, diversity and dominant species of larvae and juveniles and their relationship with temperature and salinity. Altogether 1 548 larvae and juveniles were caught with an average of 55 per net. The variation range of abundance value of each water layer was 80.85−312.03 ind ·km−3, with 50 m water layer being the largest, 30 m water layer being the smallest, and 15 m water layer being the smallest. The fish species number varied from 7 to 14, with a continuous increasing trend from 5 m to 50 m water layer. The abundance of larvae and juveniles in the four developmental stages was the highest at 50 m water layer. The species number and richness index showed a continuous increasing trend from shallow water to deep water, while the diversity index and evenness index increased first and then decreased. According to the IRI index, there were three main species at 5 m water layer. There were five main species at each of the other water layers, but there were some differences in their IRI index among different water layers. There was a significant positive correlation between the number of larval and juvenile fish species and their salinity (P<0.05, R=0.86). Thus, with the increase of water depth and salinity, the species number also increased. There was a significant positive correlation between the abundance of juvenile and water temperature in the upper and middle water (P<0.01, R=0.98); there was a significant positive correlation between the abundance of juvenile and salinity in the lower and middle water (P<0.05, R=0.79).
doi: 10.12131/20200218
[Abstract](86) [FullText HTML](11) [PDF 1044KB](11)
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Squid (Sthenoteuthis oualaniensis), one of the important economic Cephalopods in the South China Sea, has great development potential and economic value, playing an increasingly significant role in the marine fisheries of the South China Sea. In order to understand the variation of catch per unit effort (CPUE) and make scientific predictions, we constructed a gray prediction model GM (1,N) and combined it with marine environmental factors, then fitted and predicted the production data of the South China Sea squid from spring to summer of 2013−2019. Besides, we modified the background value of the original model by Simpson formula and Fourier series, and corrected the residual error of the simulated value. The results show that the average relative errors of the traditional GM (1,N) model and the optimized grey GM (1,N) model were 7.78% and 2.54%, respectively. For the prediction of squid CPUE in 2019, the optimized grey GM (1,N) model reduced the relative error from 4.79% of the traditional GM (1,N) model to 1.87%. It is showed that the optimized grey system model has a higher prediction accuracy than the traditional GM (1,N) model, which provides a new idea on how to predict the relative abundance of the squid resources accurately.
doi: 10.12131/20200249
[Abstract](146) [FullText HTML](45) [PDF 682KB](28)
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We analyzed the basic nutrinet composition, amino acids and fatty acid contents, texture characteristics and off-flavor compounds of muscle of Liza haematocheila cultured in in-pond raceway system (IPRS) and usual-pond system (UPS). Results show that the crude lipid content in IPRS was significantly lower than that in UPS, but the crude ash content increased significantly (P<0.05). The lysine and valine contents as well as the ratio of essential amino acids/non-essential amino acids were higher in IPRS than those in UPS (P<0.05). The total saturated fatty acid content of fish dorsal muscle in IPRS was significantly lower than that in UPS (P<0.05), but the total content of poly-unsaturated fatty acid content was significantly higher (P<0.05). The texture characteristics were all higher in IPRS than those in UPS (P<0.05). The geosmin concentration in muscle was detected in UPS, but the geosmin and 2-methylisobomeol were not observed in IPRS. The results indicate that in-pond raceway system has positive effects on improving muscle nutritional quality of L. haematocheila.
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2021, 17(2): 0-0.
[Abstract](29) [PDF 2176KB](11)
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2021, 17(2): 1-10.   doi: 10.12131/20200236
[Abstract](145) [FullText HTML](58) [PDF 1115KB](24)
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We analyzed the total number of heterotrophic bacteria and Vibrio, ammonia and nitrite nitrogen of water, survival rate of larvae, bacterial community of larvae and rearing water of Litopenaeus vannamei after different disinfection treatment of hatchery water, including iodine (I2), chlorine dioxide solution (ClO2), formaldehyde (HCHO) and bleach [Ca(ClO)2]. The results show that the total number of bacteria and Vibrio in the formaldehyde group was lower, and the number of Vibrio was the lowest. The concentration of ammonia and nitrite nitrogen in the four disinfectants groups was lower than that in the control group, and the concentration of bleach group was the lowest. The survival rate of the larvae in the formaldehyde group was significantly higher than those in the other four groups (P<0.05). The 16S rDNA high-throughput sequencing reveals that the disinfectant changed the microbial community and abundance of dominant bacteria of the hatchery water and the larvae. The bacterial composition of the hatchery water was more complex than that of the larvae, and the early stage was more complex than the late stage. Besides, the genera OM43_clade, Alcanivorax, Erythrobacter, Altererythrobacter, Tenacibaculum, Enhydrobacter and Gilvibacter were enriched in the N6−Z1 periods of rearing water; Donghicola, Cohaesibacter, Phaeodactylibacter, Candidatus-Cquiluna and Ruegeria were enriched in the M1−P1 periods of rearing water, while Vibrio, Planomicrobium, Exiguobacterium, Psychrobacter, Acinetobacter, Bacillus, Methylophaga and Halomonas had high abundance in the larvae.
2021, 17(2): 11-19.   doi: 10.12131/20200209
[Abstract](76) [FullText HTML](39) [PDF 2006KB](10)
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We analyzed 30 congeners of polychlorinated biphenyls (PCBs) in the farmed oysters (Crassostrea rivularis, C. hongkongensis, C. gigas) from the main aquaculture areas along Guangdong coast (Shantou, Shanwei, Shenzhen, Zhuhai, Jiangmen, Yangjiang and Zhanjiang) by using gas chromatography mass spectrometry (GC/MS). The detection rates of PCBs in oysters and their potential risks to human health were also evaluated. Results show that PCBs had a detection rate of 97.6% in the farmed oysters along Guangdong coast. Concentration of PCBs in oysters ranged from nd to 8.62 ng·g−1 (wet mass), with an average value of (0.57±1.23) ng·g−1. The highest PCBs concentration was found in Shenzhen, followed by Zhuhai, Shantou, Yangjiang, Jiangmen, Zhanjiang and Shanwei. The congeners of PCBs and their compositions were similar in different locations, showing that Hexa-PCBs and Penta-PCBs are the most abundant components in oysters. Compared with the shellfish in other coastal waters at home and abroad, the concentration of PCBs in this study is at a lower level. Bioaccumulation of PCBs in farmed oysters is lower than the limited residue levels of PCBs in National Food Safety Standard Limits of Pollutants in food in China and the hygienic standard for shellfish in European Union. The carcinogenic risk and hazard quotient of PCBs in oysters are less than the threshold value of the US Environmental Protection Agency, indicating that the carcinogenic risk of indicator PCBs in Guangdong oysters is at an acceptable level for consumers.
2021, 17(2): 20-27.   doi: 10.12131/20200202
[Abstract](114) [FullText HTML](35) [PDF 858KB](23)
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Pennahia macrocephalus, one of the major commercial fishes in the Beibu Gulf, is of great significance to study its stocks status. Based on the biological data of P. macrocephalus collected in the Beibu Gulf from 2006 to 2014, we estimated the asymptotic body length (L), relative natural mortality (M/k), relative fishing mortality (F/k), relative total mortality (Z/k), optimal body length-at-first-capture (Lc_opt), exploitation rate (E) and relative biomass index (B/B0) by the length-based Bayesian biomass estimation method (LBB). Results show that the average L and Lc_opt were 265 mm and 157 mm, respectively, and the relative mortality rates of M/k, F/k and Z/k were 1.39, 3.58 and 4.96, respectively. The Lc_opt of P. macrocephalus showed an increasing trend while the L showed a decreasing trend. At present, the E of P. macrocephalus is relatively high (0.58), indicating the resources have been in the state of overexploited. The B/B0 is less than 0.5, indicating the overexploitation of current stocks.
2021, 17(2): 28-35.   doi: 10.12131/20200221
[Abstract](110) [FullText HTML](35) [PDF 2883KB](10)
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Blue shark (Prionace glauca) is a widely distributed pelagic species with relatively high catch rate of longline fishery targeting tunas. Based on the 51-trip observer data for the blue sharks collected in the Western Central Pacific Ocean during 2015–2018, we anayzed their catch rate, sex proportion and fork length. The results show that higher catch per unit effort (CPUE) was found in the area of 170°30'E−124°50'W and 33°30'N−34°40'S. It is noted that the CPUE fluctuated greatly during 2015−2018 (highest in 2017). There was no significant difference between CPUE and month (P>0.05). The distribution range of male and female was basically the same. The sex ratio for female and male was 1.75. The dominant fork length (FL) for both male and female ranged from 160 cm to 220 cm, accounting for 89.26% and 85.19%, respectively. There was significant distribution difference between male length and female length by t-test (P<0.05).
2021, 17(2): 36-43.   doi: 10.12131/20200179
[Abstract](131) [FullText HTML](52) [PDF 1219KB](18)
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In order to reveal the bone morphology of Thunnus tonggol, we studied its skeletal system by X-ray fluoroscopy imaging and manufacturing technique of bone specimen. It is found that the skeleton of T. tonggol consists of appendicular skeleton and axial skeleton. Its appendicular skeleton includes belt bone and branched fin bone, and the axial skeleton consists of skull, spine and coccyx. The cranial skeleton of T. tonggol consists of neurocranium and splanchnocranium. The neurocranium is divided into ethmoidale, frontale, sphenoid and occipitale. The splanchnocranium is surrounded by the bones at the front of the digestive tube, and it includes arcus mandibularis, arcus hyoideus, arcus branchialis and opercular bones. The spine of T. tonggol is composed of 39 vertebraes, and the neural spine and haemal spine of the 35th–38th centrum deformed into epural and hypural. The 39th centrum evolved into the urostyle. The study on skeletal system of T. tonggol not only enriches the biological basis of the genus Tunas, but also provides references for its classification and evolution.
2021, 17(2): 44-50.   doi: 10.12131/20200005
[Abstract](113) [FullText HTML](45) [PDF 1021KB](36)
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To explore the structure of the spleen of Pelteobagruvs vachelli and the location of its blood-spleen barrier, we observed its spleen in morphology, size, histology and in vivo staining. The results show that the spleen of P. vachelli was located in the middle of the abdominal cavity with dark red colour, and the spleen body index was 0.120%–0.273%. Paraffin sections of healthy spleen were prepared and stained with HE and modified James, and the microscopic observation reveals that the spleen tissue was mainly composed of underdeveloped capsule system, unclear boundary between red and white pulp, and fibers that were composed of reticular fibers and collagen fibers. Reticular fibers were mainly located around the splenic cord and ellipsoid; collagen fibers were mainly located in the splenic cord. We applied Trypan blue in vivo staining method to explore the position and function of the blood-spleen barrier, and found that Trypan blue was mainly located in the ellipsoid endothelial cells of the spleen, and first appeared at 4th hour after injection. It accumulated in the ellipsoid gradually along with time, and the number increased significantly after 24 h, and continued to increase until 72nd hour. It is shown that the ellipsoid endothelial cells are an important component of the blood-spleen barrier.
2021, 17(2): 51-59.   doi: 10.12131/20200229
[Abstract](102) [FullText HTML](43) [PDF 668KB](19)
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In order to analyze and evaluate the muscle nutritional composition and value of bigeye tuna (Thunnus obesus), bluefin tuna (T. thynnus) and yellowfin tuna (T. albacares) near Mischief Reef, the South China Sea, we applied the national standard method to evaluate their water, protein, ash, fatty acid and amino acid composition. The results show that yellowfin tuna had the highest protein content, while bluefin tuna has the highest fat content and ash content. With amino acid score (AAS) and essential amino acid index (EAAI) as scoring criteria, the amino acid scores of three tuna species were greater than or equal to 1. The essential amino acid compositions of the three tuna species were better than FAO/WHO model. The oleic acid content of bluefin tuna was significantly higher than those of the other two species (P<0.05). Most mono-unsaturated fatty acid (MUFA) and poly-unsaturated fatty acid (PUFA) were detected in bluefin tuna with highest contents. It is indicated that all of the three tuna species had richer nutrients, higher nutritional ratio and value. Yellowfin tuna provided more protein, while bluefin tuna provided more unsaturated fatty acids. Thus, the bigeye tuna, bluefin tuna and yellowfin tuna near Mischief Reef have high development value, and the composition detection has important guiding significance for further research, design special domestication and breeding feed ingredients of these three tuna species.
2021, 17(2): 60-69.   doi: 10.12131/20200214
[Abstract](127) [FullText HTML](32) [PDF 4348KB](6)
Abstract:
The morphological changes of mitochondria rich cells (MRCS) in gills of juvenile goldfish (Scatophagus argus) were studied by microscopic technique under the stress of sudden salinity drop (20 salinity group put into 5 salinity group) and salinity sudden rise (20 salinity group put into 35 salinity group). The results show that the long and short diameters of MRCs were (9.517±1.390) μm and (7.150±1.448) μm, respectively, significantly higher than those of the control which were (7.317±0.986) μm and (7.317±0.986) μm (P<0.05), respectively; and the MRCs number increased significantly at 6th hour. Two types of MRCs were discovered: Type I MRCs, oval in shape with irregular nuclei, well-developed inner ridges and closed or open apical openings; Type II MRCs, round, with regular round nuclei and multiple apical openings. With different shapes of mitochondria, Type a mitochondria were slightly stained, showing short and thick shape; Type b mitochondria were more deeply stained, showing small granular. The results indicate that juvenile S. argus will produce a response mechanism through the changes of MRCs volume, quantity, shape and structure, as well as the shape and structure of mitochondria in order to maintain the stability of internal environment.
2021, 17(2): 70-77.   doi: 10.12131/20200167
[Abstract](116) [FullText HTML](49) [PDF 957KB](10)
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In this study, we investigated the expression of FMRFamide in vivo of Onchidium reevesii after inflammatory stimulus, and the molecular mechanism of FMRFamide polypeptide maintaining homeostasis. Based on a fragment of FMRFamide gene from the transcriptome of O. reevesii, we obtained the full-length cDNA of FMRFamide gene as 2 618 bp by RACE (Rapid-amplification of cDNA ends), including an open reading frame (ORF, 882 bp) which encoded a total of 293 amino acids. The results of the phylogenetic tree suggest that the FMRFamide gene of O. reevesii was most closely related to that of Lymnaea stagnalis, which is consistent with traditional morphological classification. The qRT-PCR results indicate that FMRFamide mRNA was distributed in different tissues of O. reevesii, but the expression in ganglion was very significantly higher than that in skin, hemocyte, hepatopancreas, muscle, gonad and pleopod (P<0.01). Immunohistochemistry verified the consistency of the FMRFamide peptide with mRNA distribution in tissues. The inflammatory stimulation experiment shows that the mRNA expression levels of FMRFamide gene in ganglia, hepatopancreas, hemocyte and skin were significantly higher in the experimental group than in the control group after lipopolysaccharide (LPS) injection (P<0.05), reaching the maximum value at 12th hour after stimulation. In conclusion, O. reevesii FMRFamide is mainly found in ganglia and is involved in collective immune regulation through neuroendocrine system, playing a significant role in maintaining the stability of tumefaciens in vivo under inflammatory stimuli.
2021, 17(2): 78-86.   doi: 10.12131/20200223
[Abstract](105) [FullText HTML](57) [PDF 836KB](20)
Abstract:
Lateolabrax maculatus with initial body mass of (7.2±0.07) g had been fed for 56 d with five diets containing 0 (N0), 0.4% (N1), 0.8% (N2), 1.2% (N3) and 1.6% (N4) taurine, so as to investigate the effects of taurine on the growth performance, digestive enzymes, antioxidant capacity and immune indices of L. maculatus. The results show that the dietary taurine improved the weight gain rate (WGR), specific growth rate (SGR) and feed rate (FR) of L. maculates significantly (P<0.05) , especially for N2, N3 and N4 groups. The whole-body crude protein content increased but lipid content decreased with the increase of dietary taurine level (P<0.05). The activities of protease and lipase in taurine supplemented groups were significantly higher than those in the control (P<0.05). The levels of red blood cell (RBC) and white blood cell (WBC) were significantly higher in taurine supplemented groups than those in the control (P<0.05), and hemoglobin (Hb) levels in N2, N3 and N4 were higher than that in the control (P<0.05). The total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities in taurine supplemented groups were significantly higher than those in the control (P<0.05). The malondialdehyde (MDA) contents in taurine supplemented groups were significantly lower than those in the control (P<0.05). The linear regression analysis on the weight gain rate indicates that the optimal dietary taurine level for growth of L. maculates is 0.85%.
2021, 17(2): 87-96.   doi: 10.12131/20200193
[Abstract](118) [FullText HTML](45) [PDF 1082KB](25)
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In order to investigate the effects of taurine on the intestinal microflora structure and immune function of Trachinotus ovatus, we used fish meal, fermented soybean meal and corn gluten meal as the basic protein sources to prepare the nitrogen and fat feed with taurine contents of 1.3 g·kg−1 (T0), 4.4 g·kg−1 (T1), 7.4 g·kg−1 (T2), 10.5 g·kg−1 (T3), 12.7 g·kg−1 (T4), respectively. Seven hundred and fifty individuals of T. ovatus with an average body mass of (80.0±0.5) g were randomly devided into five groups with three replicates of fifty fish, and the experiment lasted 56 d. Sequencing results show that a total of 87 707 sequences had been obtained in the intestine of T. ovatus. The number of OTUs that can be annotated to the database was 5 130 (95.32%). At phylum level, Proteobacteria, Tenericutes and Spirochaetes were the predominant phyla. Alpha diversity and beta diversity analyses show that the richness and diversity of intestinal microbial in T2 group were the lowest and the species composition was significantly different between T1 and T4 groups (P<0.05). The serum lysozyme activity, C4, and Ig increased significantly with the addition of exogenous taurine (P<0.05). The expression of ToTLR-1, ToTLR-2, ToTNF-α and ToIL-1β in each group decreased significantly (P<0.05). The expression of ToNFkB P65 of T1, T2 and T4 groups was significantly lower than that of the control group (P<0.05), while the expression of ToIL-10 of T3 and T4 groups was significantly higher than that of control group (P<0.05). The results indicate that exogenous taurine has a significant impact on intestinal microflora and immune function.
2021, 17(2): 97-103.   doi: 10.12131/20200197
[Abstract](151) [FullText HTML](37) [PDF 959KB](12)
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In this study, agar was modified by carboxymethylation, hydrogen peroxide oxidation and hydroxypropylation to compare the solubility, color, gel transparency, gel texture, IR molecular structure and thermal stability before and after the modification, aiming to explore the influence of three modification treatments on the physicochemical properties of agar. The results show that the dissolving temperature, gelling temperature, melting temperature and gel strength decreased significantly after carboxymethylation and hydroxypropyl treatments (P<0.05), whereas the soft elasticity and water holding capacity of agar gel improved; the gel strength of agar was improved by oxidation treatment (P<0.05), from 984 g·cm−2 to 1 463 g·cm−2; after oxidation and hydroxypropylation, the modified agar showed higher whiteness (P<0.05), while carboxymethyl agar was on the contrary (P<0.05). Besides, all modifications had increased the transparency of agar gel significantly (P<0.05). The thermal stability increased with oxidation and hydroxypropylation, but reduced with carboxymethylation. In conclusion, three modification methods can improve physicochemical properties of agar at different extents.
2021, 17(2): 104-113.   doi: 10.12131/20200211
[Abstract](95) [FullText HTML](34) [PDF 1276KB](20)
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Taking Litopenaeus vannamei of different forms (whole shrimp, decapitated shrimp, shrimp meat) as research objects, we applied Illumina high throughput sequencing technology to identify the surface microbial composition and changes of samples during partial freezing storage. The results show that: 1) The operational taxonomic units (OTUs) number of all samples decreased with the extension of storage time. After four weeks of storage, the whole shrimp and the decapitated shrimp had more OTUs, and the OTU number in shrimp meat was the least. 2) Chao, ACE and Shannon indices of all samples decreased but Simpson index increased, which indicates that the abundance and diversity of samples reduced during the storage. 3) At genus level, Vibrio was the main microorganism of all samples at the beginning, and Arcobacter existed more in the decapitated shrimp and the whole shrimp. After four weeks of storage, Pseudomonas, Shewanella and Psychrobacter became the dominant spoilage bacteria. 4) The heatmap and key species analysis at genus level show that the composition and proportion of three forms of shrimp samples were different. Therefore, different forms of L. vannamei had different microbial compositions and abundance in various storage periods. It is necessary to inhibit the advantages of microorganisms specifically to ensure the quality of the products during the cold chain process.
2021, 17(2): 114-121.   doi: 10.12131/20200220
[Abstract](90) [FullText HTML](35) [PDF 652KB](8)
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To investigate the changes in the basic properties of surimi gel after the first and second heating stages, we studied the surimi gels of five kinds of freshwater fish (Pelteobagrus fulvidraco, Ctenopharyngodon idellus, Aristichthys nobilis, Cirrhinus molitorella, Hypophthalmichthys molitrix) by indices of gel properties, chemical bonds, lipid content, phospholipid content and so on. The results show that the gel strength, hardness, chewiness, whiteness and water holding capacity of the first heating surimi gel were significantly less than those of the second heating surimi gel (P<0.05), but there were no significant differences in the elasticity and cohesion. The surface hydrophobicity of the five kinds of fish surimi gels increased significantly after the second stage of heating, and the degree was significantly different (P<0.05). However, there was no significant difference in the disulfide bond content between the two heating stages of A. nobilis and P. fulvidraco (P>0.05). The lipid content of the second heating surimi gel ranged from 38.24 g·kg−1 to 76.45 g·kg−1, and the total phospholipid ranged from 1.929 mg·g−1 to 3.452 mg·g−1.
2021, 17(2): 122-128.   doi: 10.12131/20200169
[Abstract](151) [FullText HTML](55) [PDF 810KB](23)
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The experiment was conducted to investigate the effects of simulated transportation for 24 h with three transport densities (D1=14 kg·m−3, D2=21 kg·m−3, D3=28 kg·m−3) and six different transport durations (T1=4 h, T2=8 h, T3=12 h, T4=16 h, T5=20 h, T6=24 h) at 7 kg·m−3 on the transport water quality, resuscitation rate and antioxidant capacity of juvenile Lates calcarifer. The results show that with the increase of transport density and duration, the contents of NH4 +-N and NO2 -N in the transport water increased, while the DO content, pH and resuscitation rate decreased but the survival rate was 100%. The results of transport density test show that the T-SOD activities in D1 and D2 groups were significantly lower than that in the control group (P<0.05); the POD activity in D3 group were significantly lower than those in D1 group, D2 group and the control group (P<0.05); the MDA content in D2 group was not significantly different from that in D3 group, which was significantly higher than those in D1 group and control group (P>0.05). The results of transport time test show that there was no significant difference in T-SOD activity between T3 and T4 groups, which were significantly higher than those in T1, T2, T5 and T6 groups (P<0.05); the POD activity in each experimental group was significantly higher than that in the control group (P<0.05); the MDA content in T2 group was not significantly different from that in T4 group, but was significantly higher than those in T1, T3, T5, T6 groups and control group (P<0.05). It is shown that with the increase of transport density and duration, the water has deteriorated and the resuscitation rate decreased, having significant effect on the antioxidant ability of L. calcarifer juveniles. In conclusion, under conditions of water temperature 24 ℃, salinity 32 and pH 7.92, with body length of (1.42 ± 0.19) cm, the density should not exceed 21 kg·m−3 for 24 h.
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doi: 10.12131/20210048
[Abstract](0)
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Investigation on artificial marking technology is a very important supporting work for national fish mark release recapture and effectiveness tracing evaluation issues. In this study, two-month old juvenile black carp (Mylopharyngodon piceus) were immersed in alizarin complexone (ALC) at a concentration of 100 mg·L−1 for 48 h, and then transferred to normal water for 20 d. Three pairs of otoliths (i.e., sagitta, lapillus and asteriscus) were removed from the black carps by continuous sampling and observed under fluorescence microscope and photographed, so as to evaluate the characteristics of deposition and the marking effect of ALC in different otoliths. The results show that the marked areas were clearly observed in each otolith pair under visible light and different excitation light, with a 100% mark success rate. After 20 d of recovery culture in normal water without ALC, the intensity of ALC mark in otoliths of the marked fish was still very high, reflecting a good marking effect. Moreover, the optimum light source was blue excitation light, followed by green excitation light. The lapillus was the optimal otolith type for ALC marking and for judgment of time lag among the three pairs of otoliths, followed by asteriscus. In addition, there was a time lag of 1 day between the carps immersed in ALC solution and ALC deposition into otolith, as well as between the removing immersed carps from ALC solution and disappearance of ALC mark from otolith.
doi: 10.12131/20210040
[Abstract](4)
Abstract:
In this study, soft tissues of fresh oyster (Crassostrea ariakensis) were used as the experimental material for the determination of glycogen, and the optimal reaction conditions were determined by comparing and analyzing the absorbance values of different anthrone sulfuric acid ratios and different reaction times, and then the lowest detection limit, stability and accuracy of this method were evaluated. Finally, a trace detection system for the determination of oyster glycogen content was established. The results show that the volume of the optimized micro-reaction system was 300 μL, mainly including 200 μL of 0.2% anthrone sulfuric acid solution and 100 μL of the sample solution; the reaction time in the boiling water bath was 10 min. The minimum detection limit of glucose was 0.001 5 mg·mL−1, and the coefficient of variation of the standard curve was less than 4%, which indicates that this method has high detection sensitivity and good repeatability; after the reaction completed, absorbance was basically unchanged within 120 min at room temperature, which means that the stability of this reaction is also high; the recovery rate of the six tissue of oyster mantle, gill, lip, gonad, hepatopancreas and adductor muscle were between 95.3% and 105.8%, indicating that this method has high accuracy. Therefore, the method for the determination of oyster glycogen in a micro-reaction system has the advantages of small reagent consumption, simple operation and low cost per sample. Besides, this method has high repeatability, stability and accuracy, so it is suitable for batch determination of large quantities of samples. The study provides an effective technical method to complete the glycogen detection of oyster samples more quickly and efficiently.
doi: 10.12131/20210027
[Abstract](4)
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To study the performance and influence factors of equipment for deep-water cage cleaning, we applied numerical simulation method and prototype testing to investigate the biofouling removal rate of cleaning equipment with different inlet pressures and nozzle diameters, and then we explored the biofouling removal mechanism of aquaculture net cage under the action of cavitation jet. The numerical simulation results show that the maximum gas volume fraction of nozzle showed an increasing trend when the nozzle diameter was 0.6−1.0 mm under rated flow, and the maximum gas volume fraction value of d=1.0 mm nozzle was 37.5%. The flow velocity of the jet 40 mm away from the nozzle outlet decreased by 85.57%−96.98%, and the velocity of the nozzle decreased significantly in submerged environment. Further water tank cleaning test results show that when the input pressure was 18.8 MPa and the diameter value of nozzle was 0.8 mm, the largest cleaning rate of aquaculture nets of the cleaning equipment was 79.76%. The shellfish fouling organisms mainly fell off in the form of shell breaking under the impact of cavitation jet of cleaning equipment. After the cleaning, most of the residues was the soft foot silk tray of shellfish with strong adsorption. The soil on the surface of the net was completely removed and presents the primary color of the breeding net.
doi: 10.12131/20210019
[Abstract](2)
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In order to understand the community structure of zooplankton in the main freshwater rivers of Jiangmen, Guangdong Province, we investigated the zooplankton community structure in Tanjiang River, Yinzhou Lake and Xijiang River during December 2016 to October 2017. Altogether 157 species of zooplankton had been observed, including 74 species of rotifers, 43 species of protozoa, 21 species of cladocers, 19 species of copepods. The annual average density and biomass of zooplankton were 1 651 ind·L−1 and 0.80 mg·L−1, respectively. The density of protozoa was the highest (1 164 ind·L−1). And the highest biomass of rotifers and copepods was 0.37 and 0.31 mg·L−1, respectively. Compared with the historical level, the species number of large zooplankton has decreased significantly, while the small zooplankton has increased significantly. And the density of zooplankton increased significantly, while their biomass decreased significantly. The Shannon-Wiener diversity index H′ was 1.05−4.36, and the Pielou index J′ was 0.23−1.15. There were 30 dominant species in the survey area, and the number of protozoa was the largest (15 species). Among the dominant species, 10 were eutrophic indicator species, all of which were rotifers. Dominant species of the indicator species for eutrophic water were only distributed in Tanjiang River and Yinzhou Lake, indicating that Xijiang River water quality is the best.
doi: 10.12131/20210001
[Abstract](9)
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In this paper, we investigated the effects of water temperature, photoperiod and light intensity on the survival, feeding and growth of Schizothorax biddulphi juveniles by using experimental ecological methods; predicted the optimal growth conditions for the juveniles by Box-Benhnken design; and studied the saline alkali tolerance of juveniles by single factor static toxicity acute test. The results show that: the survival rate of the juveniles was above 85% at 5−25 ℃. The feeding rate, length growth rate and specific growth rate reached the maximum values at 20 ℃. When the photoperiod was 16 L: 8 D and the light intensity was 500 lx, all the indices of the juveniles reached the maximum values. Under conditions of water temperature of 12.98 ℃, daily light time of 15.07 h, and light intensity of 670.27 lx, the best survival, feeding and growth were obtained. The LC50 of NaCl salinity was 401, 3.62, 3.29 and 2.92 g·L−1 at 24, 48, 72 and 96 h, respectively, and the safety concentration (SC) was 0.89 g·L−1. The LC50 of NaHCO3 alkalinity was 97.14, 86.75, 80.26 and 74.52 mmol·L−1 at 24, 48, 72 and 96 h, respectively, and the SC was 20.75 mmol·L−1.
doi: 10.12131/20210071
[Abstract](21)
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To explore the protective effect of oyster (Crassostrea hongkongensis) enzymatic ultrafiltration components on triptolide (TP)-induced oxidative damage of TM4 Sertoli cells in mice (Mus musculus), we detected the molecular mass distribution and trace metal element content of the oyster hydrolyzed ultrafiltration components, and compared the cell viability, GSH content, MDA content and ROS level of TM4 cells induced by TP by ultrafiltration components. The results show that the oyster hydrolyzed ultrafiltration components are rich in trace metal elements such as copper, zinc, manganese and selenium; most small molecules and macromolecular substances were separated by ultrafiltration; compared with the model group, ultrafiltration components improved the cell viability of TM4 cells induced by TP. The cell viability of <3, 3–5 and 5–10 ku ultrafiltration fraction was higher than that of >10 ku ultrafiltration fraction; <3 ku ultrafiltration fraction could prevent TP-induced oxidative stress damage in TM4 cells, reduce the production of intracellular reactive oxygen species and lipid peroxidation, and enhance the antioxidant activity of TM4 cells.
doi: 10.12131/20210020
[Abstract](11)
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In order to determine the trawl depth quickly, improve the fishing efficiency and reduce the cost of fishery production, the paper proposes a method for calculating the optimal fishing depth of the specified fish target based on the sonar device metadata. Sonar device metadata structure is relatively complex and contains a large number of redundant data. In the paper, the original data were simplified, and the information of seabed depth and target strength was calculated and extracted. The effective data range and noise data range were determined according to the type of target fishery resources. After filtering the noise data, the effective data was displayed in the form of statistical chart. The target fishery resources of each depth were counted. The relationship between depth and target fishery resources was constructed, and the optimal fishing depth was calculated and predicted by various methods. The results show that the optimal fishing depth of krill (Euphausiaceorum, target intensity −69.5–−40.8 dB) was 172.9–187 m in the survey area. According to the sonar data obtained in a certain sea area over a period of time, the optimal fishing depth of the target fishery resources in that sea area can be calculated quickly. The method in the paper provides references for actual marine production at sea.
doi: 10.12131/20210056
[Abstract](11)
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The Schizochytrium limacinum hydrolysate (SLH) was prepared from defatted S. limacinum residue, so as to analyze its Maillard reaction conditions. Besides, we explored the antioxidant activities of Maillard reaction products (MRPs) from the isolated fractions of SLH by ultrafiltration and sephadex gel column chromatography. The optimal Maillard reaction parameters were obtained as follows: mass ratio (ribose: peptide) 1∶1, pH 9, temperature 100 ℃, and time 6 h, resulting in reducing power activity and DPPH radical scavenging rate of 1.24 (5 mg·mL−1) and 88.62% (12.5 mg·mL−1), respectively. The SLH was ultra-filtered to obtain the fractions of SLH-1 (<5 kD), SLH-2 (<10 kD) and SLH-3 (<50 kD). It is found that the SLH-1 has the strongest antioxidant capacity before and after Maillard reaction. Then the SLH-1 is further separated by Sephadex G-25 gel column to obtain the fractions of SLH-1-Ⅰ, SLH-1-Ⅱ, SLH-1-Ⅲ and SLH-1-Ⅳ. The higher molecular weight fraction of SLH-1-Ⅰ had higher antioxidant activity after Maillard reaction (the reducing power activity was 0.741 at 2 mg·mL−1 and the DPPH free radical scavenging rate was 79.41% at 5 mg·mL−1). Amino acid composition analysis shows that Maillard reaction can decrease the contents of Tyr, Lys, His, Arg and Trp, etc. However, there is no obvious change in the content of essential amino acids after Maillard reaction.
doi: 10.12131/20210005
[Abstract](14)
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According to the biological survey of bottom trawl fishery conducted in Daya Bay in the summer of 2017 and the winter of 2018, we analyzed the basic characteristics of the stable isotope of carbon and nitrogen in fishery organisms by using carbon and nitrogen stable isotope techniques. In addition, we constructed a continuous trophic level spectrum, and discussed the differences in the nutritional structure of fishery organisms in different seasons. The results show that the range of stable carbon and nitrogen isotope values of main fishery species in Daya Bay were −19.66‰−15.19‰ [Average: (−17.26±0.86) ‰] and 11.63‰−16.01‰ [Average: (13.59±0.96) ‰], respectively. We used the average nitrogen stable isotope of small zooplankton as a benchmark to construct the trophic level spectrum of fishery organisms, and found that the trophic level of fishery organisms in Daya Bay ranged from 2.99 to 4.28. The trophic level of fish had the widest span and a more complex diet. We calculated six quantitative community indices of trophic structure of macrobenthos by using the SIBER model, and found that some organisms shared the preys, and there was a phenomenon of niche overlap. In addition, the community nutrition redundancy in summer was lower than that in winter.
doi: 10.12131/20210070
[Abstract](19)
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In order to comprehensively understand the settlement performance of falling-net, as well as to provide references for the development of falling-net model test and the improvement of fishing gear and method, we conducted the sea trials in the central-southern South China Sea in March 2016, and studied the settlement performance of falling-net based on polynomial regression and generalized additive model (GAM). The results show that: 1) Free settlement was a more critical factor affecting the total settlement depth. 2) 90.0~119.9 s was an appropriate free settlement time based on the settlement performance of the falling-net. 3) The free settlement speed firstly increased in a short time and then decreased, with the maximum value occurring at the time of 10 s. The damping settlement speed remained relatively stable in the first 50 s with little change, but then decreased rapidly. 4) Free settlement time (Tf), wind speed (Sw), the direction angle between wind and current (\begin{document}$\alpha$\end{document}) had significant influences on free settlement depth. Tf, Sw, drift speed of fishing boat (Sb) and \begin{document}$\alpha$\end{document} had significant influences on damping settlement depth. The study suggests that: 1) The influence of Sw and \begin{document}$\alpha$\end{document} on free settlement depth and damping settlement depth is complex and non-linear, and they may affect the settlement of falling-net through waves and changing the relative position between the fishing boat and falling-net. 2) Sb has a significant influence on damping settlement depth. This may be caused by that Sb affects the degree of closure of net-mouth and the hauling of purse line.
doi: 10.12131/20210018
[Abstract](19)
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Longline tuna fishery in the Indian Ocean is an important part of offshore fisheries in China. Water temperature at different depths can affect longline albacore catch rates. In this paper, the generalized additive model (GAM) was used to analyze the relationship between the spatial distribution of albacore (Thunnus alalunga) catch rate and water temperature at different depths based on fishery data and corresponding Argo buoy data during 2008 to 2017. The results show that the spatial distribution of albacore tuna catch rate was significantly affected by the sea surface temperature (0 m), water temperature at depth of 200 and 400 m. The optimal GAM model explained the variance of catch rate (Catch per unit effort) by 53.3%, and the determining coefficient of model fitting was 0.527. The catch rates of albacore tuna had a nonlinear relationship with the temperature of the three selected water layers. High catch areas are concentrated at the surface layer of 17~30 ℃, 200 m deep sea area of 17~2 ℃, and 400 m deep sea area of 9~15 ℃. Besides, we derived the relationship between the spatial distribution of albacore tuna catch rate in South Indian Ocean and the temperature of three water depth sections for the first time, and the results provide technical support for guiding the rational production of albacore tuna in the Indian Ocean.
doi: 10.12131/20200250
[Abstract](15)
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In order to make use of interspecific competition to co-culture beneficial microalgae and construct excellent algal forms in ponds, we designed different temperature gradients (10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃ and 35 ℃) and different initial density ratios (Navicula pelliculosa: Chlorella vulgaris was 1: 10, 1: 1, 1: 0.1, respectively) for the experiment in this study, to investigate the effects of temperature and initial density ratios of N. pelliculosa and C. vulgaris on their growth and competition. The results show that the cell density of N. pelliculosa in mono-culture group increased first and then decreased at 10−15 ℃, and increased gradually at 20−30 ℃ with a maximum value of 0.50 × 106 cells∙mL−1; 25−30 ℃ was the optimal growth temperature for N. pelliculosa which could not survive at 35 ℃. C. vulgaris grew slowly or even stopped at 10−15 ℃, and grew rapidly at 20−35 ℃ in mono-culture group. The maximum value of the cell density was 14.15 × 106 cells∙mL−1. The optimal growth temperature was 35 ℃. The growth rate of N. pelliculosa in mixed culture was higher than that in mono-culture group, and increased gradually with the increase of proportion of C. vulgaris. The maximum cell density of N. pelliculosa in mixed culture was significantly higher than that in mono-culture group. The smaller the initial cell density was, the faster C. vulgaris grew in mixed culture. The growth rate of 1: 0.1 group was significantly higher than that in mono-culture group, and the growth rate of 1: 10 group was significantly lower than that in mono-culture group. The competitive inhibition parameter data show that C. vulgaris had little competitive inhibition on N. pelliculosa, and α value increased with the increase of temperature and proportion of C. vulgaris, while β value increased with the increase of temperature and proportion of N. pelliculosa. The two microalgae can coexist peacefully.
doi: 10.12131/20210043
[Abstract](27)
Abstract:
In this study, we examined two sizes of Nile tilapia (Oreochromis niloticus) [Large: (21.56±0.27) g, Small: (5.92±0.03) g] to explore their tolerance to carbonate alkalinity. Different carbonate-alkalinity solutions were prepared with NaHCO3 to carry out the following experiments: 1) Fish were directly transferred from fresh water to 30 or 22 g·L−1 carbonate alkalinity solutions to determine the mortality. 2) Fish were acutely exposed to different carbonate alkalinity solutions ranging from 6 to 10 g·L−1 for 96 h. 3) For chronic alkaline acclimation experiments, carbonate concentrations increased gradually at three levels of +2, +4 and +6 g·(L·d)−1. The results show that the half lethal alkalinities of Nile tilapia under acute stress for 96 h ranged from 6.25 g·L−1 to 9.01 g·L−1. The alkaline tolerance of Nile tilapia is weaker than that of fish which adapt to extreme alkaline environment (e.g. Gymnocyprinus przewalskii), but it is still stronger than that of most freshwater cultured fish. At juvenile stage, The tolerance of Nile tilapia to carbonate stress was significantly enhanced when its body mass increased more than three times. Nile tilapia can be acclimated by daily alkaline increment of 2 g·L−1. The relationship of "time-alkalinity-mortality" under acute alkaline stress can be well fitted by complementary log-log model.
doi: 10.12131/20210016
[Abstract](38)
Abstract:
Photosynthetic bacteria (PSB) were isolated and purified from marine environmental samples from different areas by double-layer plate coating method and scribing method. Vibrio parahaemolyticus, V. vulnificus and V. anguillarum were used as control. The inhibition of marine photosynthetic bacteria was determined by Oxford cup method, and the degradation of nitrite nitrogen (NO2 -N) and ammonia nitrogen (NH4 +-N) by different strains was determined by naphthalene ethylenediamine hydrochloride spectrophotometry and indophenol blue spectrophotometry. The results show that three strains of photosynthetic bacteria were isolated from 30 sea water and mud samples, and the strain P-3 isolated from the seawater samples of cheniushan island in Lianyungang had strong inhibitory effect on three kinds of Vibrio, and had the strongest effect on V. anguillarum, with the inhibition zone diameter of 5.3 mm. The results show that all the three photosynthetic bacteria have certain ability to degrade NO2 -N and NH4 +-N, and strain P-3 had the strongest ability to degrade NO2 -N and NH4 +-N. the degradation rates of strain P-3 were 89.68% and 94.98%, respectively, when cultured in the medium containing 50 mg·L−1 NH4 +-N and NO2 -N for 4 d. P-3 was identified as Rhodopseudomonas palustris by morphological observation, physiological and biochemical tests and 16S rDNA sequence analysis.
doi: 10.12131/20200256
[Abstract](20)
Abstract:
We investigated the growth, photosynthetic pigment and color change of Betaphycus gelatinae at different light intensities (1 000, 3 000, 5 000, 7 000 and 9 000 lx). Based on CSE-1 imaging chromaticity detection and analysis, we studied the correlation of color parameter L*a*b*(CIE 1976) with light intensity, growth and photosynthetic pigment. The results show that the relative growth rate and weight gain rate increased significantly with the increase of light intensity. The suitable light intensity for growth was 7 000−9000 lx. However, when the light intensity was 1 000 lx, there was no obvious growth of B. gelatinae. With the increase of light intensity, the contents of chlorophyll a, carotenoids, phycoerythrin and phycocyanin generally decreased, and the color of B. gelatinae gradually changed from reddish brown to green. The tristimulus values (XYZ) showed a significant distribution difference on the CIE 1931 chromaticity diagram at different light intensities. Light intensity was significantly positively correlated with lightness L*(P<0.05), but significantly negatively correlated with red-green value a*(P<0.01). There was a significant positive correlation between relative growth rate with lightness L* and yellow-blue value b*(P<0.05). Chlorophyll a was significantly negatively correlated with lightness L*(P<0.05), but significantly positively correlated with red-green value a*(P<0.05). Both phycoerythrin and phycocyanin were significantly positively correlated with the red-green value a*(P<0.05).
doi: 10.12131/20200255
[Abstract](15)
Abstract:
Four treatment groups with five replicates per group were designed including high fish meal group (42%, FM), low fish meal group (22%, T0), and taurine supplementation groups (0.2%, 0.5% inclusion) in low fish meal feed (T0.2, T0.5). Then the four diets were fed to rice field eel (Monopterus albus) with initial body mass of (26.67±0.02) g for 10 weeks, so as to evaluate the effects of dietary taurine supplementation in low fish meal feed on the growth, digestibility, intestinal enzyme activities of rice filed eel. The results show that compared with FM group, the weight gain rate, protein efficiency ratio, dry matter digestibility, and protein digestibility of rice field eels decreased in T0 group significantly (P<0.05), while the feed conversion ratio increased significantly (P<0.05). Adding an appropriate amount of taurine could increase the weight gain rate, protein efficiency ratio and dry matter digestibility of rice field eels, and reduce the feed coefficient (P<0.05). The weight gain rate, protein efficiency ratio and protein digestibility in T0.5 group were approximate the same in T0 group (P>0.05). Moreover, comparing with FM group, the intestinal creatine kinase, Na+K+ATPase, alkaline phosphatase, trypsin and lipase activities in T0 group decreased significantly (P<0.05), but the activities of the aforementioned intestinal enzyme increased significantly after adding 0.2% taurine (P<0.05). The activities of Na+K+ATPase, alkaline phosphatase, trypsin and lipase in the T0.5 group were higher than those in T0 group, but there was no significant difference (P>0.05). To sum up, 0.2% taurine supplementation in low fish meal feed can improve the growth performance, intestinal digestion and absorption function of rice field eel, but excess taurine (0.5%) has no obvious effect.
doi: 10.12131/20210051
[Abstract](37)
Abstract:
Disease problems have seriously threatened the development of Crassostrea hongkongensis aquaculture. Thus, finding suitable biomarkers for C. hongkongensis health assessment is important for preventing C. hongkongensis diseases. We investigated the effects of salinity stress, ammonia stress, immune stimulation and air exposure stress on the immune activities of C. hongkongensis. The results show that the CAT activity increased significantly under both low-salt (Salinity 3) and high-salinity (Salinity 30) stress (P<0.05). High-salt stress also increased SOD and NOS activities significantly (P<0.05). The stress of high concentration of ammonia nitrogen (60 mg∙L–1) caused a significant decrease in the CAT activity (P<0.05), while the activities of ACP and SOD increased significantly (P<0.05) under both high and low concentration of ammonia nitrogen (6 mg∙L–1) stress. Both Vibrio harveyi and lipopolysaccharide stimulation inhibited the CAT activity significantly (P<0.05). In addition, the CAT activity during air-exposure stress at 4 and 25 ℃ showed a significant decreasing trend (P<0.05). Therefore, CAT is more sensitive to environmental changes than other immunological indicators, which may be a health-related evaluation index of C. hongkongensis.
doi: 10.12131/20210030
[Abstract](22)
Abstract:
A variety of fish, including Chinese tongue sole (Cynoglossus semilaevis), have sexual size dimorphism, and this growth dimorphism may be related to the interaction of sex steroid hormones and growth axis-related genes. For the early stage of this study, transcriptomics analysis has found that sex steroid hormones might be involved in the growth regulation of Chinese tongue sole. In order to explore the effect of sex steroid hormones on the growth difference of different sexes of Chinese tongue sole, we injected 16-month-old female, male and pseudo-male fish with estradiol and testosterone hormones, and measured the growth hormone 1 (gh1), insulin-like growth factor 1 (igf1) and suppressor of cytokine signaling 3 (socs3) for quantitative analysis. The results reveal that the two sex steroid hormones had inhibitory effects on the growth performance of individuals of different sexes of Chinese tongue sole. After the treatment, the expressions of gh1 and igf1 in the brain and liver showed an overall downward trend, and the expression of socs3 in the muscle and liver increased significantly, indicating that the growth performance of fish had declined. By exploring the effects of sex steroid hormones on the growth performance of different sexes of Chinese tongue sole, we provide references for the in-depth study of sex steroid hormones in the regulation of fish sex size abnormalities.
doi: 10.12131/20210026
[Abstract](27)
Abstract:
To optimize the structure of bottom trawl with lagre-size mesh, we took a typical domestic single bottom trawl with large mesh as research object. Based on L9(34) orthogonal table, we designed the orthogonal tests, in which there were factors such as the ratio of total length of the net to perimeter (L/C), the ratio of the headline length to groundline length (S1/S2), and the ratio of net body length to the total length of nets (Lb/L). Besides, we applied the mean and extreme difference analysis method to detect the influence of above structure parameters on resistance (R), vertical expansion of trawl mouth (H) and the energy consumption coefficient (Ce). The results show that with different horizontal expansion, the influence of three factors on R followed an order of L/C>S1/S2 >Lb/L, that on H followed an order of S1/S2>Lb/L>L/C, and that on Ce followed an order of L/C>S1/S2>Lb/L. The L/C of this type of trawl should be relatively small compared with that of trawl with small-size mesh, and the smaller the L/C is, the smaller R will be. Under these conditions, L/C=0.2 is the optimal value when vertical expansion of bottom trawl and energy consumption coefficient were used as indicators. Compared with small-size mesh trawl, S1/S2 should be higher, and the higher the S1/S2 is, the better the vertical expansion of the net mouth will be. Within the range of 0.83–0.99, S1/S2 had no significant impact on the resistance, and S1/S2=0.99 is the optimal value when the energy consumption coefficient is taken as the indicator. Lb/L decreased with the increase of mesh size, but the decreasing range gradually decreases. Lb/L=0.65 should be suitable for medium or low speed trawl, while Lb/L=0.75 should be more suitable for high speed and fastly towing.
doi: 10.12131/20210022
[Abstract](18)
Abstract:
We evaluated the effects of low salinity pressure on the survival rate, osmotic pressure, biological tissue and immunity enzymes activities of Sipunculus nudus which was cultured for 96 h in water with abrupt salinity drop of 0 (S30), 5 (S25), 10 (S20), 15 (S15), 20 (S10) and 25 (S5). The results show that: 1) S. nudus could tolerate the salinity drop of 10, but would die when the salinity dropped of over 15. 2) The coelomic fluid of S. nudus increased with the decrease of water salinity significantly, and there was a significant positive correlation between the body mass and coelomic fluid volumn (R2>0.96. 3) The osmotic pressure and body protein contents decreased with the decrease of water salinity (P<0.05). 4) In the low salinity treatments, the connective tissue of longitudinal and circumferential muscle fibers of the body wall were thin, and the staining of columnar cells was lighter. For the tentacle, its adhesion ability was weaker as the epithelial cells became larger. 5) SOD and CAT activities in the groups of S30 and S25 were relatively stable, while the body SOD and coelomic fluid CAT in the groups of S10 and S15 first decreased and then increased, however, the CAT of coelomic fluid in the groups of S10 and S15 first increased and then decreased. SOD and CAT activities in the coelomic fluid had strong varation. In summary, low salinity pressure can affect the survival rate, osmotic pressure, biological tissue and immunity enzymes activities of S. nudus significantly.
doi: 10.12131/20200262
[Abstract](24)
Abstract:
Based on Foshan and Taiwan populations of Micropterus salmoides, we established four populations including Foshan inbreeding group (Foshan ♀× Foshan ♂), Taiwan inbreeding group (Taiwan ♀ × Taiwan ♂), normal progeny (Foshan ♀× Taiwan ♂) and reciprocal progeny (Taiwan ♀ × Foshan ♂), in order to compare their growth and morphological characteristics after six-month culture. Results show that the growth performance and coefficient of variation for body mass were significantly higher in the hybid groups than in the two inbred groups. The results of morphological analysis shows that the morphological differences of the four populations were mainly concentrated in the middle part of trunk and tail. The contribution rate of the first three principal components was 92.9%, and that of the first principal component was 71.3rs which mainly reflected the morphological characteristics of the front and middle part of the body. The contribution rate of the second principal component was 16.6%, reflecting the characteristics of the tail region of fish body. In the scatter plot of the scores of the first two principal components, the four populations could be completely distinguished due to the low overlap area. The stepwise discriminant model constructed by combining measurable characters and frame characteristics shows the highest accuracy (86.7%~96.0%). The results provide references for the growth and morphological identification of hybrid families of Micropterus salmoides from Foshan and Taiwan populations.
doi: 10.12131/20210042
[Abstract](35)
Abstract:
Norovirus (NoV) is the main pathogen of non-bacterial acute gastroenteritis. Oysters are important carriers for the spread of NoV, which can enrich NoV from contaminated seawater and environment through filter feeding. People tend to eat raw or lightly cooked oysters, which may cause NoV infections. About half of the foodborne diseases associated with oysters are caused by NoV. Reverse transcription fluorescent quantitative PCR (RT-qPCR) is the main method for detecting NoV, but it cannot distinguish infectious from non-infectious viruses effectively. Since NoV cannot be cultured in vitro, RT-qPCR has limitations in assessing the effectiveness of inactivation methods for NoV. Porcine gastric mucin (PGM) and propidium monoazide (PMA) and other nucleic acid intercalators combined with RT-qPCR have shown potential applications in the detection of infectious NoV. High hydrostatic pressure treatment is an effective method to reduce norovirus in shellfish, and the pressure of over 400 MPa can inactivate NoV significantly. In this paper, we review the enrichment of NoV in oyster, detection methods to distinguish infectious NoV and the inactivation of high hydrostatic pressure technology on NoV in Pacific oysters (Crassostrea gigas), Pleated oysters (Alectryonella plicatulas) and Kumamoto oysters (C. sikamea), so as to understand the research progress in controlling NoV in oysters, and to provide references for the establishment of effective NoV risk warning and non-thermal inactivation technology in the future.
doi: 10.12131/20200258
[Abstract](41)
Abstract:
To explore the probiotic potential of Candida ethanolica GXU01 in tilapia culture and to find ecological and friendly feeding bacteria for tilapia sustainable cultivation, we used C. ethanolica GXU01 as feed-additive to feed tilapia. Then we determined the growth performance, intestinal digestive enzymes, serum non-specific immune indexes, intestinal microbial community structure, and challenged the tilapia with Streptococcus agalactiae, so as to comprehensively evaluate the effects of Candida ethanolica GXU01 on the growth and immunity of tilapia. The results show that the growth performance, digestive enzyme activity, serum lysozyme activity and complement C3 content of tilapia could be significantly improved by feeding C. ethanolica GXU01 (P<0.05). The abundance of Fusobacteria, Cetobacterium and Akkermansia in the intestinal tract of tilapia increased significantly and those of Cyanobacteria decreased significantly after feed of C. ethanolica GXU01. In the challenge test, the survival rate of tilapia fed with diet containing C. ethanolica GXU01 increased by 26.66%. The study shows that Candida ethanolica GXU01 promotes the intestinal digestive ability and immune resistance of tilapia.
doi: 10.12131/20210028
[Abstract](27)
Abstract:
To investigate the effects of dietary polysaccharide from Endothelium corneum gigeriae galli (PEGG) supplementation on the growth, digestive, intestinal antioxidant capacity and serum biochemical indices of Lates calcarifer, we had fed juvenile L. calcarifer [Body mass of (11.85±1.66) g] by basal diets with PEGG at 0 (Control group), 5 (Low-dose group), 20 (Medium-dose group) and 80 g·kg−1 (High-dose group) was for eight weeks. The results show that compared with the control group, PEGG supplementation groups increased the final body mass, weight gain rate and specific growth rate of juvenile L. calcarifer, and the difference was significant in the high-dose group (P<0.05). PEGG supplementation groups increased digestive enzyme activity significantly (P<0.05). PEGG supplementation groups improved the histological structure of intestine significantly, indicating that PEGG increased the fold height, fold width and muscular thickness significantly (P<0.05). Intestinal antioxidant capacity was enhanced significantly. The superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) activity, the concentration of increased glutathione (GSH) and total antioxidant capacity (T-AOC) increased in the PEGG supplementation groups, while malondialdehyde (MDA) concentration decreased significantly (P<0.05). Serum biochemical indices were improved. Cholesterol in all treatment groups decreased significantly, while ALT and AST in medium-dose group decreased significantly (P<0.05). In conclusion, dietary PEGG improves the digestive capacity, antioxidant capacity and serum biochemical indices of juvenile L. calcarifer, and can promote the growth performance. The suitable PEGG supplementation level is 20 g·kg−1.
doi: 10.12131/20200242
[Abstract](41)
Abstract:
In order to find out the current status of the population structure and growth characteristics of grass carp (Ctenopharyngodon idellus) in the middle and lower reaches of the Pearl River, we investigated the grass carp population from 2019 to 2020. The results show that the body length of grass carp was 103−665 mm [average: (347.89±96.73) mm]. The body mass was 21.4−6 650.0 g [average: (986.87±842.96) g]. The population was composed of 0+−5+ age groups, dominant for 1+−3+, accounting for 92.8% of the total number of samples. The body length had a significant power function relation with body mass for uniform motion pattern. Growth could be described by Von Bertalanffy equation with the growth parameters: L=1187 mm, k=0.128, t0=−0.282, W=31 344.51 g. The index of length growth performance (φ) of grass carp was 5.26, and the growth inflection age was 8.29. The total mortality rate, natural mortality rate, fishing mortality rate and exploitation rate were 0.44, 0.15, 0.29 and 0.66, respectively. The sex ratio (Females/males) was 1.07: 1. Sexual maturation was mainly at Stage II. Compared with the previous data, the growth performance and fecundity of grass carp all showed a decline tendency; the population structure tended to be miniaturized. In order to promote the recovery of grass carp resources in the middle and lower reaches of the Pearl River, it is recommended to reduce the fishing intensity. Besides, the catch body length should be greater than 791 mm and the mass should be greater than 9 279.11 g.
doi: 10.12131/20200049
[Abstract](28)
Abstract:
We established a numerical model for calculating the dynamic characteristics of a triangular high-density polyethylene (HDPE) deep-water aquaculture cage in waves and current based on the finite element method. To verify the accuracy of the numerical model, we carried out a series of physical model tests on the single-point mooring (SPM) cage under the conditions of pure wave and combined wave-current, in which the model scale was set at 1: 15. The relative error between the numerical and experimental results was within 10%. Afterwards, considering the sea state of the prototype cage, the calculated parameters for waves and currents were as follows: wave heights 4–6 m, period 9 s, current velocity 0.5–1.5 m·s−1. We analyzed the deformation of the floating collar and the mooring force of the cage with single-point mooring (SPM) and multiple-point mooring (MPM). Besides, we discussed the effect of the mooring pattern on the motion characteristics of the cage. The results show that under the conditions of wave and current, the peak value of MPM force was higher than SPM force, and the difference became greater with the increase of velocity and wave height. Under the condition of severe waves and strong currents, the MPM system can reduce the deformation of the floating collar. However, the mooring pattern had little influence on the heave of the cage collar. For the MPM system, the x-axis displacement of the collar was greater than that of the SPM system, in which the difference was 25.64%. During a wave period, the xz plane profiles of the net deformation under sea conditions were almost the same for the two different mooring systems.
doi: 10.12131/20210021
[Abstract](19)
Abstract:
In order to study the hydrodynamic performances and motion amplitude response characteristics of the mariculture ship composed of truss structure and several floating bodies with plate and frame structures, we calculated the hydrodynamic characteristics of the ship in frequency domain based on the three-dimensional potential flow theory and Morrison equation. Then we obtained and analyzed the hydrodynamic parameters and motion response of the mariculture ship. The results show that the additional mass and radiation damping of the mariculture ship are sensitive to the change of frequency, and the sensitivity is obviously different in the movement of the mariculture ship in different directions, and the additional mass and radiation damping of the rotational motion are larger than those of the plane motion, which are both closely related to the structural shape of the mariculture ship. Under the action of incident waves in every direction, the first-order wave force of the mariculture ship increase at first and then decrease with the increase of frequency, and the first-order wave force curve tends to be stable in the high frequency section under the action of incident waves in different directions. However, there is a big difference in the middle and low section. Under the action of high-frequency and low-frequency excitation, the motion response of the mariculture ship is small, but the resonance occurs when it moves in the medium and short period regular waves. The surging and pitching are the main motion modes when ship with follow wave or head wave condition, and roll and heave motions are the main motion modes in bean wave.
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