DIETARY PHENYLALANINE REQUIREMENT OF JUVENILE GIBEL CARP

Abstract

A 55d growth trial was conducted to quantify the phenylalanine requirement of juvenile gibel carp (3.19±0.03)g by feeding isonitrogenous (380 g/kg crude protein) and isocaloric(17.80 kJ/g gross energy)test diets, which contained casein and gelatin as intact protein with graded phenylalanine levels (0.58%, 0.78%, 0.98%, 1.18%, 1.38%, 1.58% and 1.78% of dry matter, respectively), and constant tyrosine level in each diet. L-crystalline amino acids (CAA) were supplemented corresponding to the amino acid pattern found in the muscle protein of gibel carp except for phenylalanine. Nonessential amino acids (except tyrosine and cystine) were supplemented to make diets isonitrogenous. The measured dietary phenylalanine levels were 0.73%, 0.89%, 1.09%, 1.26%, 1.33%, 1.58% and 1.67%, respectively. Thirty fish were randomly stocked in 130L indoor polyvinyl quadrate tank(water volume 120L; water flow speed 200mL/min)and fed experimental diets at satiation by hand in continuous one hour at 9:00 and 16:00 twice a day. Weight gain (WG) (194.50%), specific growth rate (SGR) (1.96%) and feed conversion efficiency (FE) (37.74%) were significantly (P0.05) higher in fish fed the diet containing 1.09% phenylalanine (P0.05) than the other treatments. Protein efficiency ratio (PER), protein retention efficiency (PER) and energy retention efficiency (ERE) were also significantly higher at 1.09% dietary phenylalanine level (P0.05). With the increase of dietary phenylalanine level, whole body ash content decreased gradually; serum glucose and triglyceride contents increased significantly (P0.05) and then showed a downward trend, in contrary, the contents of liver lipid and serum cholesterol were observed the opposite trend. However, no significant differences were found in condition factor(CF), hepatosomatic index (HIS), the contents of whole body moisture, protein, lipid and energy, serum albumin content and liver transaminases (GPT and GOT) among different treatments (P0.05). Based on the polynomial regression analysis of SGR and FE data, it is recommended that the diet for juvenile gibel carp should contain phenylalanine at 1.09% of dry diet respectively, corresponding to 30.2 g/kg dietary protein for optimum growth and efficient feed utilization with tyrosine fixed at 1.04% of dry diet.