Dietary Lysine And Methionine Requirements And Substitution Of Fish Meal In Diets For Juvenile Trachinotus Ovatus

Three experiments were conducted to investigate the dietary lysine and methioninerequirements of golden pompano (Trachinotus ovatus), and the suitable replacement offish meal by other plant protein source.(1) Dietary Lysine Requirements of Juvenile Pompano (Trachinotus ovatus)Six formulated diets was conducted to study the lysine requirement of Trachinotusovatus, with six graded levels of lysine (2.28%,2.46%,2.63%,2.73%,2.95%and3.28%). Each diet was randomly assigned to triplicate groups of20juvenile fish (meaninitial wet weight14.78±0.41g) in seawater floating net cages (1.0×1.0×1.5m). Fishwere fed twice daily (08:00and16:00) to apparent satiation for56days. The resultsshowed that weight gain (WG) and specific growth rate (SGR) increased withincreasing dietary lysine levels, WG and SGR of fish fed diets containing2.95%and3.28%lysine were significantly higher than those of fish fed diets containing2.28%,2.46%and2.63%(P<0.05)，while no significant differences were found in weight gainand specific growth rate among fish fed diets containing2.95%and3.28%lysine(P<0.05). Feed coefficient decreased with increasing dietary lysine levels, and feedcoefficients in shrimp fed diets containing2.95%and3.28%lysine were significantlylower than that in shrimp fed diets containing2.28%,2.46%and2.63%lysine. Dietarylysine levels significantly affected glutamic-pyruvic transaminase (ALT) and totalprotein (TP)(P<0.05). NO significant differences (P>0.05) were found in glucose(GLU), cholesterol (CHO) and triglyceride (TG) among diet groups. Broken-lineregression analysis on weight gain indicated that the optimum dietary lysinerequirement for maximum growth of Trachinotus ovatus was2.94%of diet (DM basis)or6.70%of dietary protein.(2) Dietary Methionine Requirements of Juvenile Pompano (Trachinotus ovatus)Six diets was conducted to determine the dietary methionine requirement ofjuvenile golden pompano. Diets were formulated with six graded levels of methionine(0.86%0.92、1.04、1.15、1.32、1.45%). Each diet was randomly assigned to triplicategroups of20juvenile fish (initial body weight12.40±0.02g) in seawater floating netcages (1.0×1.0×1.5m). Fish were fed twice daily (08:30and16:00) to apparent satiationfor56days. The results showed that WG and SGR increased with increasing levels of methionine up to1.15%diet (P<0.05) and remained nearly the same trend thereafter.Second-degree polynomial regression analysis on WG and SGR indicated that theminimum recommended dietary methionine requirement for optimal growth of juvenilepompano was1.28%of the dry diet, corresponding to2.98%of dietary protein. Hence,the corresponding requirements of this fish for total sulfur amino acids (Met+Cys) werecalculated to be1.48%of diet (3.44%of dietary protein). Additionally, the estimatedrequirements for the other essential amino acids were calculated from A/E ratios ofwhole body amino acid profile based on the lysine requirement determined from thepresent experiment. Except aspartate aminotransferase (AST), significant differences(P<0.05) were found in alanine aminotransferase (ALT), total protein (TP), glucose(GLU), cholesterol (CHO) and triglyceride (TG) among diet groups.(3) Replacement of fish meal by mix plant proteins in diets for Trachinotus ovatusThe third experiment was conducted to evaluate the suitable level of substitutionof dietary fish meal by gradual substitution (25-100%) of corn soy bean, corn glutenmeal and soybean concentration protein. Moreover, crystalline lysine and methinoinewere added to the same gradual diets according to balance the contents of dietary lysineand methionine. Nine isonitrogen (43.45) and isocaloric (11.09) were fed to juvenile T.ovatus (mean initial wet weight6.26±0.07g) for56days. Each diet was randomlyassigned to triplicate groups of25juvenile fish in seawater floating net cages(1.0×1.0×1.5m) and fed twice daily (08:00and16:00) to apparent satiation. The resultsshowed that the survival of T. ovatus beyond92%without significant difference. Themaximum values of WG and SGR were found at25%substitution of fish meal. And theminimum value of feed coefficient was also found at25%substitution of fish meal. Thechange patterns of WG and SGR during the rearing period was decreased withincreasing substitution of fish meal by other plant protein source. The protein contentsof whole fish and muscle significantly decreased when the substitution beyond25%.The digestive enzyme activity of liver decreased with increasing substitution of fishmeal. And serum glucose, triglycerides (TG) and aspartate aminotransferase (AST)were also significantly affected by the level of substitution of fish meal.