Dietary phenylalanine requirement for fingerling grass carp (Ctenopharyngodon idella)

Abstract:

A feeding experiment was conducted to assess the dietary phenylalanine requirement for fingerling grass carp (Ctenopharyngodon idella). Seven isonitrogenous diets with graded levels of phenylalanine ranging from 0.82% to 2.12% (% Dry matter) were fed to triplicate groups of fish with an average initial body weight of 13.21g for 56 days, respectively. The results show that weight gain rate, feed efficiency and protein retention efficiency increased with increasing of dietary phenylalanine level from 8.2 g/kg to 12.0 g/kg, but appeared to keep stable with further increasing to 21.2 g/kg. And whole fish body protein was affected significantly by dietary phenylalanine level (P<0.05). However, fish survival rate, viscerasomatic index, hepatosomatic index, condition factor and whole fish body moisture, lipid and ash were not affected significantly by dietary phenylalanine level (P>0.05). The broken-line regression analysis with weight gain, feed efficiency and protein retention efficiency as the criteria indicated that the requirements of dietary phenylalanine for fingerling grass carp were 12.73 g/kg, 12.20 g/kg and 12.55 g/kg of dry diet respectively. In conclusion, the dietary phenylalanine requirement for fingerling grass carp was estimated to be 12.20-12.73 g/kg dry diet(with 5.5 g/kg tyrosine in diet), and 3.39%-3.54% of the dietary crude protein.