Effect of dietary replacement of fish meal with low-gossypol cottonseed protein concentrate on growth performance and expressions of genes related to protein metabolism for swimming crab (Portunus trituberculatus)

Abstract

An eight-week feeding trial was conducted to evaluate the effect of dietary replacement of fish meal with low-gossypol cottonseed protein concentrate (CPC) on growth performance, body composition, amino acid profiles in tissues, antioxidant capacity and the expression levels of genes related to protein metabolism and inflammation for juvenile swimming crab (Portunus trituberculatus). Six isonitrogenous and isolipidic diets (450 g kg−1 protein and 80 g kg−1 lipid) were formulated to contain graded levels of CPC, and fish meal was replaced with CPC at 0, 10%, 20%, 30%, 40% and 60% levels (CPC00, CPC10, CPC20, CPC30, CPC40 and CPC60), free gossypol concentrations in experimental diets were analyzed to be 0, 32.62, 66.10, 106.71, 133.13, 192.21 mg kg−1 respectively. Arginine, lysine and methionine were added to ensure consistency of these three essential amino acids in all experimental diets. Each diet was randomly assigned to triplicate groups of 30 juvenile swimming crabs (approximately initial weight 7.59 ± 0.06 g) that were stocked in rectangle plastic baskets. Results of present study indicated that crabs fed the CPC60 diet had the lower final weight (FW), percent weight gain (PWG), specific growth rate (SGR) and feed efficiency (FE) than those fed the CPC20 diet, and crabs fed the CPC20 and CPC30 diets had the highest survival among all treatments, and the lowest survival was occurred at crabs fed the CPC60 diet. The hepatopancreas color was blackened with the replacement levels of fish meal with CPC increasing from 0% to 60%. Free gossypol concentration in hepatopancreas significantly increased with increase of dietary replacement levels of fish meal with CPC. Crabs fed the CPC40 and CPC60 diets had lower lipid content in whole body than those fed the other diets. Arginine, lysine, methionine and isoleucine contents in muscle were significantly influenced by dietary replacement levels of fish meal with CPC. ALT, AST, TP, ALB, HDL and ALP in hemolymph, and T-AOC, ALT, AST, SOD, GSH, GSH-ST in hepatopancreas were significantly affected by dietary replacement of fish meal with CPC. Dietary replacement levels of fish meal with CPC could influence the expressions of genes related into protein metabolism such as tor, akt, s6, s6k1, 4ebp1, eif4e1a, eif4e2, eif4e3, antioxidant and immune such as gpx, cat, cMnsod and lysozyme, as well as growth such as tlr4, irak4, myd88, traf6, and inflammation such as relish. In conclusion, based on two slope broken-line and quadratic broken-line regression analysis of PWG against the dietary replacement of fish meal with CPC, the optimal replacement level of fish meal with CPC was estimated to be 19.07% and 22.73% for juvenile swimming crab, respectively. Results demonstrated that CPC could partially replace fish meal, but had no negative effects on growth performance, antioxidant activity and immunity of swimming crab.