Abstract:A 67-days feeding experiment was conducted to investigate the effects different levels on the growth performance and biochemical parameters of tiger puffer [average body weight: (13.83±0.63) g], and to determine the dietary methionine requirement for tiger puffer. There were six experimental isonitrogenous and isolipidic semipurified diets which were formulated with the graded levels of methionine (0.61%, 0.85%, 1.10%, 1.39%, 1.60%, 1.84%, respectively). Each diet was randomly assigned to triplicate groups, and each group contained 30 individuals. Fish were fed fourth daily(07:00, 12:00, 16:00, 20:00) to apparent satiation. The result showed that no significant differences in protein productive value (PPV) were found among dietary treatments (P>0.05). Specific growth rate (SGR), feed conversion ratio(FCR) and protein efficiency ratio (PER) increased with increasing dietary methionine levels from 0.61% to 1.60%(P<0.05), the higest group was observed in methionine levels 1.60% group, and there after showed a declining tendency with increasing dietary methionine levels from1.60% to 1.84%. Hepatosomatic index (HSI) and viscerosomatic index (VSI) of the 1.60% methionine diets was significantly higher than that of 0.61% groups (P<0.05), with further increase from 1.60% to 1.84%, HSI and VSI decreased. The crude lipid contents of whole body were significantly affected by dietary methionine levels (P<0.05), the 1.60% methionine diets was significantly higher than 0.61% groups (P< 0.05), with further increase from 1.60% to 1.84%, crude lipid decreased. while moisture, crude protein and ash showed no significant differences (P>0.05). Dietary methionine levels significantly influenced the contents of triglyceride, bile acid and blood glucose in serum (P<0.05), There were no significant difference in total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, total protein, activity of glutamic-pyruvic transaminase and glutamic-oxaloacetic transaminase (P>0.05) in serum. Second-order regression analysis on the basis of SGR indicated that the optimum dietary methionine requirements of tiger puffer were estimated to be 1.38% of diet (2.71% of dietary protein).
