Vitamin D₃ requirement of grouper (Epinephelus coioides) in practical diet

Six isonitrogenous and isoenergetic diets supplemented with different levels of vitamin D₃ (0, 1 000 IU·kg⁻¹, 2 000 IU·kg⁻¹, 4 000 IU·kg⁻¹, 8 000 IU·kg⁻¹, 100 000 IU·kg⁻¹) were formulated to evaluate the requirement of vitamin D₃ to Epinephelus coioides, namely Diet 1, Diet 2, Diet 3, Diet 4, Diet 5 and Diet 6. Diet 3 obtained higher weight gain rate, specific growth rate and feed efficiency than the other groups (P<0.05). With dietary supplemental vitamin D₃ higher than 2 000 IU·kg⁻¹, the intraperitoneal fat ratio (IPF) and viscerosomatic index (VSI) decreased significantly with increasing dietary vitamin D₃ levels (P<0.05). The protein contents in whole body and muscle decreased with increasing dietary vitamin D₃ levels (P<0.05), but the lipid and ash contents showed no difference in whole body and muscle among all the groups. When the dietary supplemental vitamin D₃ was lower than 2 000 IU·kg⁻¹, the calcium (Ca) and phosphorus (P) contents in fish bone were positively correlated with the vitamin D₃ levels. Based on Ca and P contents in bones, the optimal supplementation level of vitamin D₃ in practical diet should be 2 000 IU·kg⁻¹.