Effects of dietary amino acid patterns on growth and protein metabolism of large yellow croaker (Larimichthys crocea) larvae

This study was conducted to evaluate the effects of dietary amino acids (AA) patterns on growth, survival, activities of digestive enzymes and aminotransferases and target of rapamycin (TOR) gene expression of large yellow croaker (Larimichthys crocea) larvae. The control diet was produced using intact protein as the only protein source. Four isonitrogenous and isolipidic semi-purified diets were formulated with crystalline-AA replacing approximately 40% fish meal protein-bound nitrogen. The AA patterns of these diets were adjusted according to the overall AA pattern of large yellow croaker egg protein (LEP), large yellow croaker larvae whole-body protein (LLP), large yellow croaker muscle protein (LMP) and white fishmeal protein (WFP), respectively. The test diets and live copepod were fed to triplicate groups of larvae (initial body weight 3.15 ± 0.15 mg) five times (6:00, 8:30, 12:30, 14:30, and 17:00) daily for 30 days. The results showed that specific growth rate (SGR) of fish fed the WFP diet was significantly higher than LEP or LLP diet (P < 0.05). At the end of the growth trial, there was no significant difference in survival rate among larvae fed LEP, LLP, WFP and the control diet (P > 0.05), whereas the highest value was recorded in larvae fed the LLP diet, followed by WFP, the control, LEP and LMP diet, respectively. Whole-body crude protein content was significantly higher in larvae fed the WFP diet compared to the LEP or LLP diet (P < 0.05). Larvae fed the live copepod had significantly higher whole-body crude protein and lipid contents than that in larvae fed artificial microdiets (P < 0.05). Whole-body moisture content was not significantly affected by dietary treatments (P > 0.05). The specific activities of digestive enzymes and the ratio “pancreatic enzyme in intestinal segment/pancreatic enzyme in pancreatic segment” were significantly higher in fish fed the WFP diet than fish fed LLP and LEP diet (P < 0.05). Specific activities of alanine and aspartate aminotransferases were significantly higher in fish fed the WFP diet compared to the other treatments (P < 0.05). No significant differences were observed in larvae body TOR gene expression among dietary treatments (P > 0.05). Results of this study indicated that white fishmeal protein amino acid pattern was a more suitable amino acid pattern in diets of large yellow croaker larvae compared to the amino acid pattern of LEP, LLP, and LMP.