THE UTILIZATION AND REQUIREMENT OF DIETARY LYSINE FOR JUVENILE GIBEL CARP

Two experiments were conducted to investigate the utilization of crystal amino acids and the dietary requirement of ly-sine for juvenile gibel carp (Carassius auratus gibelio). Two kinds of formulated diets supplemented with crystal lysine or methionine were fed to fish and blood were sampled and plasma free amino acids content were determined. A 69-day growth trial was conducted to determine the quantitative dietary lysine requirement using diets containing white fish meal as the main source of protein, supplemented with crystalline amino acids. Seven isonitrogenous and isocaloric diets containing graded levels of lysine (1.82, 2.32, 2.82, 3.32, 3.82, 4.32 and 4.82g/100g, dry diet)were formulated. Fish were randomly stocked in triplicate groups in 5621 indoor flow2through tanks. The fish were fed to apparent satiation during the experiment. The results showed that juvenile gibel carp is able to absorb dietary crystalline lysine and methionine, the highest content of free lysine and free methionine in plasma were observed at 3h after feeding. The highest specific growth rate (SGR), final body weight and carcass weight/ body weight (CW/ BW) were observed at 3.32% dietary lysine, while hepatosomatic index(HSI) was lowest. The apparent digestibility coefficients of dry matter was significantly affected by dietary lysine contents, and the highest value was observed at 3.82% group (PPP>0.05). The activity of liver glutamic-oxalacetic transaminase (AST) and the glutamic-pyruvic transaminase (ALT) was not significantly affected by dietary lysine. AST and ALT was highest at 4.82% group. Haemoglobin was highest at 2.82% group, and lowest at 4.82% group. With the increase in dietary lysine, the content of serum urea increased significantly (P<0.05) while the number of red blood cell decreased. The optimal dietary lysine requirement for maximum growth of Carassius auratus gibelio was 3.27%of dry matter or 8.52% of protein based on broken-line regression.