Utilization Of Dietary Crystalline Lysine And Methionine And The Requirements For Gibel Carp

A short-time absorption trial of crystalline amino acids and two growth trials for requirements were conducted to investigate the utilization of dietary crystalline amino acids and requirement for gibel carp (Carassius auratus gibelio). In the short-time experiment, two diets containing crystalline lysine or methionine were used. Blood samples were drawn from the caudal vein of 3h, 6h, 9h, 12h, 15h and 24h after the last feeding. Free lysine and methionine concentration in plasma were investigate the absorbability of dietary crystalline lysine and methionine.A 69-day growth trial was conducted to determine the dietary lysine requirement for juvenile gibel carp using diets containing white fish meal as the main protein source. Supplemented with crystalline amino acids, seven isonitrogen and isocaloric diets containing graded levels of lysine (1.82%, 2.32%, 2.82%, 3.32%, 3.82%, 4.32% and 4.82% of dry matter) were formulated.In the experiment for methionine requirement, seven isonitrogen and isocaloric diets containing soybean meal, gelatin and white fishmeal as the source of intact protein were formulated and graded levels of methionine (0.32%, 0.57%, 0.82%, 1.07%, 1.32%, 1.57% and 1.82% of dry matter) were obtained with the supplementation of crystalline methionine. The trial lasted for 58 days.The results are shown as the follows:1. Juvenile gibel carp is able to utilize dietary crystalline lysine and methionine, the content of plasma free lysine and free methionine decreased 3h after feeding.2. The optimal dietary lysine requirement for maximum growth of gibel carp was 3.27% of dry matter or 8.52% of dietary protein. The optimal dietary methionine requirement for maximum growth was 0.69% of dry matter or 1.68% of dietary proteinwhile total sulfur amino acid requirement was 1.11% of dry matter or 2.71% of dietary protein.3. The highest specific growth rate (SGR), final body weight and carcass weight/body weight (CW/BW) was observed at 3.32% dietary lysine group, while hepatosomatic index (HSI) was lowest.4. With the increase in dietary lysine, the content of serum urea increased significantly while the amount of red blood cells decreased.5. Either deficiency or excess of dietary methionine significantly reduced specific growth rate (SGR), feeding rate, protein retention efficiency (PRE) and energy retention efficiency (ERE).6. Apparent digestibility coefficients of dry matter, crude protein, gross energy was not significantly affected by dietary methionine levels.7. Fish body dry matter, protein, lipid and energy increased with increasing dietary methionine up to the optimal level, then significantly decreased. No significant differences was found in body ash content at different dietary methionine levels.In conclusion, gibel carp can successfully use dietary crystalline lysine and methionine. The lysine and methionine requirements for maximum growth was estimated to be 8.52% and 1.68% of dietary protein and total sulfur amino acid was 2.71%.