Optimal Requirements Of Branch Chain Amino Acids And Histidine In Diets Of Japanese Seabass, Lateolabrax Japonicus And Large Yellow Croaker Pesudosciaena Crocea R.

Feeding trials were conducted to estimate dietary branch chain amino acids (leucine, isoleucine and valine) and histidine requirements of Japanese seabass, Lateolabrax japonicus and large yellow croaker, Pseudosciaena crocea R. in seawater floating net cages (1.5×1.5×2.0 m or 1.0×1.0×1.5 m) for 8 weeks. Results of the present studies are presented as follows:(1) With increasing dietary leucine, specific growth ratio (SGR) of Japanese seabass first significantly increased, and decreased (P<0.05). SGR were the highest in fish fed diet with 2.70% Leu (Diet 4) and decreased with increasing leucine. SGR of Japanes seabass fed the diet with 3.88% Leu (Diet 6) was significantly lower compared to Diet 4. However, no significant differences were observed between other groups and Diet 6. These results indicated that leucine was essential for growth of Japanese seabass. Japanese seabass was able to utilize crystalline forms of leucine, but less or beyond the optimum requirement level for Japanese seabass, it would depress the growth of fish. On the basis of SGR, the optimum dietary leucine requirements of juvenile Japanese seabass was estimated by using second-order polynomial regression analysis to be 2.38% of diet (5.67% of dietary protein).(2) With increasing dietary leucine, SGR of large yellow croaker first significantly increased, then decreased (P<0.05). SGR were the highest in fish fed diet with 3.30% Leu (Diet 4), and decreased with increasing leucine. SGR of fish fed the diet with 4.80% Leu (Diet 6) was significantly lower compared to Diet 4. However, no significant differences were observed between other treatments and Diet 6. The results indicated that for growth of large yellow croaker, leucine was essential. Supplemental leucine can improve the growth of large yellow croaker which was depressed due to the short of leucine. It indicated that large yellow croaker was able to utilize crystalline forms of leucine, but there was a marked decline in growth response beyond the optimum requirement level for large yellow croaker. On the basis of SGR, the optimum dietary leucine requirements of juvenile large yellow croaker was estimated to be 2.92% of diet (6.79% of dietary protein).(3) In Japanese seabass, dietary isoleucine significantly affected the growth responses of Japanes seabass (P<0.05). Final weight (FW) and SGR increased with increasing dietary isoleucine and thereafter declined. FW (30.8 g) and SGR (2.40% d-1) were the highest in fish fed diet with 1.46% Ile (Diet 3). There were no significant differences in FW and SGR between diet 3 (1.46% Ile) and diet 4 (1.89% Ile), and significantly higher compared to other treatments. The survival rate ranged from 86.7% to 97.8%, and was independent of dietary isoleucine content. Feed efficiency ranged from 0.73 to 0.86, and there were no significant differences among dietary treatments. The results indicated that, isoleucine was essential for growth of Japanese seabass, and Japanese seabass was able to utilize crystalline forms of isoleucine. On the basis of SGR, the optimum dietary isoleucine requirements of juvenile Japanese seabass were estimated to be 1.94% of diet (4.69% of dietary protein).(4) In large yellow croaker, dietary isoleucine (Ile) significantly affected the growth responses of large yellow croaker (P<0.05). FW and SGR increased with increasing dietary isoleucine, and thereafter declined. FW (20.2g) and SGR (2.38% d-1) were the highest in fish fed diet with 1.76% Ile. There were no significant differences in FW and SGR among fish fed the diet 2(1.15% Ile), diet 3(1.76% Ile), diet 4 (2.10% Ile) and diet 5 (2.41% Ile). There was a marked decline in growth response of fish fed diets with less or beyond the optimum requirement level. The change of feed efficiency was similar with SGR, and feed efficiency was the highest in fish fed diet with 1.76% Ile. No significant differences in survival were found among dietary treatment. The results indicated that for growth of large yellow croaker, isoleucine was essential, and large yellow croaker was able to utilize crystalline forms of isoleucine. On the basis of SGR and FE, the optimum dietary isoleucine requirements of juvenile large yellow croaker were estimated to be 1.71% of diet (3.98% of dietary protein) and 1.59% of diet (3.70% of dietary protein), respectively.(5) In Japanese seabass, dietary valine significantly affected the growth of Japanes seabass (P<0.05). FW, SGR and FE significantly increased with increasing dietary valine, and thereafter significantly declined. However, there were no significant differences among diet 2 (1.68% Val), diet 3 (1.91% Val) and diet 4 (2.32% Val). FW (37.3g), SGR (2.74% d-1) and FE (0.97) were the highest in fish fed diet with 1.91% Val (Diet 3). The results indicated that for growth of Japanese seabass, valine was essential and Japanese seabass was able to utilize crystalline forms of valine, but there was a marked decline in growth response of fish fed diet with less or beyond the optimum requirement. On the basis of SGR and FE, the optimum dietary valine requirements of juvenile Japanese seabass were estimated to be 2.11% of diet (5.02% of dietary protein).(6) In large yellow croaker, dietary valine significantly affected the growth responses of large yellow croaker (P<0.05). FW, SGR and FE significantly increased with increasing dietary valine and thereafter, significantly declined. However, there were no significant differences among diet 2 (1.47% Val), diet 3 (1.86% Val), diet 4 (2.34% Val) and diet 5 (2.68% Val). FW (18.2g), SGR (2.18% d-1) and FE (0.88) were the highest in fish fed diet with 1.86% Val. The results indicated that for growth of large yellow croaker, valine was essential and large yellow croaker was able to utilize crystalline forms of valine, but there was a marked decline in growth of fish fed diets with less or beyond the optimum requirement. On the basis of SGR and FE, the optimum dietary valine requirements of juvenile large yellow croaker were estimated to be 2.08% of diet (4.84% of dietary protein).(7) In Japanese seabass, dietary histidine significantly affected the growth responses of Japanes seabass (P<0.05). FW and SGR of fish fed diets less or beyond the optimum requirement level for histidine were significantly lower compared to other treatments. However, there were no significant differences among diet 2 (0.45% His), diet 3 (0.57% His), diet 4 (0.66% His) and diet 5 (0.78% His). FW (21.0g), SGR (1.72% d-1) and FE (0.81) were the highest in fish fed diet with 0.57% His (Diet 3). The results indicated that for growth of Japanese seabass, histidine was essential and Japanese seabass was able to utilize crystalline forms of histidine. On the basis of SGR, the optimum dietary valine requirements of juvenile Japanese seabass were estimated to be 0.54% of diet (1.29% of dietary protein).(8) In large yellow croaker, dietary histidine significantly affected the growth of large yellow croaker (P<0.05). FW and SGR of fish fed diets beyond the optimum requirement were significantly lower compared to other treatments. However, there were no significant differences among diet 1 (0.45% His), diet 2 (0.66% His), diet 3 (0.78% His), diet 4 (0.98% His) and diet 5 (1.24% His). FW (13.5g), SGR (1.59% d-1) and FE (0.45) were the highest in fish fed diet with 0.78% His (Diet 3). The results indicated that for growth of large yellow croaker, histidine was essential and large yellow croaker was able to utilize crystalline forms of histidine. On the basis of SGR, the optimum dietary valine requirements of juvenile large yellow croaker were estimated to be 0.87% of diet (1.98% of dietary protein).