Study On Lysine And Methionine Requirements For Juvenile Chinese Sucker, Myxocypinus Asiaticus

Two growth trials were conducted to investigate the lysine and methionine requirements for juvenile Chinese sucker (Myxocyprinus asiaticus). A56-day growth experiment was conducted to determine the optimum dietary lysine requirement for juvenile Chinese sucker using diets containing corn gluten meal, soybean meal and white fishmeal as the source of intact protein. Supplemented with L-crystalline amino acids, six isonitrogenous and isoenergetic practical diets were formulated to contain graded levels of lysine (1.23,1.80,2.39,2.98,3.56and4.18%of dry matter). In the experiment for methionine requirement, six isonitrogenous and isoenergetic practical diets (0.64,0.89,1.15,1.39,1.65and1.89%of dry matter; diet2-7) containing fermented soybean meal and white fishmeal as the source of intact protein were formulated. Diet1with fish meal as the sole protein source was used as a reference. The results are shown as follows:1. The optimum dietary lysine requirement of juvenile Chinese sucker can significantly improved its growth performance, such as weight gain, specific growth rate, protein efficiency ratio, protein productive value and feed efficiency.2. The whole-body protein significantly increased with increasing dietary lysine level, while the whole-body fat significantly decreased with it. The hepatosomatic index, condition factor and muscle essential amino acids were lowest while the dietary lysine was1.23%.3. Either deficiency or excess of dietary methionine significantly reduced weight gain, specific growth rate, protein efficiency ratio, protein productive value and nitrogen retention. The optimum dietary methionine requirement of juvenile Chinese sucker significantly promoted its growth by accelerated of body protein synthesis and reduced the deposition of fat.4. Apparent digestibility coefficients of crude protein was significantly affected by dietary methionine levels, while apparent digestibility coefficients of dry matter, fat and methionine were not significantly affected.5. The total protein, cholesterol, triglycerides, glucose, aspartate aminotransferase and alanine aminotransferase of serum were significantly affected by dietary methionine levels. 6. The broken-line analysis of WG, SGR, PER, PPV and FCR against dietary lysine level indicated that the optimum dietary lysine requirements for juvenile Chinese sucker were2.43%,2.42%,2.40%,2.49%and2.38%diet, corresponding to5.52%,5.50%,5.45%,5.66%and5.41%of the dietary protein respectively. Broken-line regression based on SGR, PER, FCR and second-order polynomial regression based on cholesterol indicated that the optimum dietary methionine level requirement for juvenile Chinese sucker was1.41%,1.42%,1.42%and1.31%diet, corresponding to3.20%,3.23%,3.23%and2.98%of the dietary protein respectively.