Dietary methionine requirement of the pre-adult gibel carp (Carassius auratus gibeilo) at a constant dietary cystine level

A 62-day growth trial was conducted to determine the dietary Met requirement of the pre-adult gibel carp (Carassius auratus gibeilo) (initial weight of 51.0 +/- 0.02 g). Six iso-nitrogenous and isoenergetic diets using fish meal, blood meal and pea protein concentrate as protein sources supplemented with crystalline amino acids were formulated to contain graded levels of dietary Met (4.44, 6.56, 8.55, 10.90, 12.79 and 15.05 g kg(-1), respectively) at a constant dietary cystine level of 3.99 g kg(-1). The results showed that weight gain rate and protein productive value significantly increased with the dietary Met levels from 4.44 to 8.55 g kg(-1), then reached plateau at 10.90 g kg(-1). Plasma HDL-C and TC were increased with dietary Met levels. Fish supplied with 4.44-8.55 g kg(-1) Met showed lower plasma AST level than that of other groups. Plasma TG, LDL-C and ALT levels were stable for all treatments. The activity of intestinal gamma-GT was increased with dietary Met levels. The optimal requirement of Met for pre-adult gibel carp (>50 g) was a range from 7.86 g kg(-1) to 9.84 g kg(-1) dry diet or 16.9 g kg(-1) to 23.0 g kg(-1) of dietary protein with the presence of 3.99 g kg(-1) Cys for the satisfied lipid metabolism and maximum growth, respectively.