Effects of fish meal quality and fish meal substitution by animal protein blend on growth performance, flesh quality and liver histology of Japanese seabass (Lateolabrax japonicus)

An 8-week growth trial was conducted to evaluate the effects of the quality of fish meal and of replacing prime steam dried fish meal (PFM) with an animal protein blend (APB with 40% poultry by-product meal, 35% meat and bone meal, 20% spray-dried blood meal and 5% hydrolyzed feather meal) on the growth performance, flesh quality and liver histology of Japanese seabass, Lateolabrax japonicus (initial body weight, 76.3+/-0.2 g). Six isoproteic (44% crude protein) and isoenergetic (19 MJ kg(-1) gross energy) diets were formulated. A control diet containing 40% PFM was designed, and 20%, 40%, 60% or 80% of the PFM was replaced by APB, in which lysine, methionine and threonine were balanced as in the control diet with crystallized amino acids; the diets were named PFM, APB20, APB40, APB60 and APB80, respectively. An additional diet with 50% standard steam dried fish meal (SFM) that completely replaced the PFM was formulated with the same profile as the control diet to compare the effect of fishmeal quality. Compared to that of fish fed the PFM diet, feed intake was significantly reduced in the SFM group and accordingly induced a lower specific growth rate (SGR, P<0.05), but this did not significantly affect the feed efficiency rate. Fish fed the diets APB20 and APB40 had comparable growth with those fed the diet PFM (control diet). Fish fed the diet with 24% or higher APB had significantly lower SGR than those fed the diet PFM (P<0.05). The reduced growth was linearly correlated to the graded lower dietary n-3 highly unsaturated fatty acids (HUFA) levels when PFM was replaced by APB. Broken-line analysis on the basis of SGR showed that the optimal level of fish meal replacement with APB was only 18.9%. Fish fed the diet with 24% or higher APB had significantly lower whole-body lipids but higher liver lipids than the PFM group (P<0.05). Polyunsaturated fatty acids (PUFA), n-3 fatty acids, n-3 HUFA and the n-3/n-6 ratio in muscle were significantly reduced at higher substitution levels of PFM by APB (P<0.05). The 18: 1n-9, EPA, DHA, PUFA, n-3, n-3 HUFA and n-3/n-6 in fish muscle were significantly correlated with the corresponding dietary contents. There were no significant differences in texture parameters for the raw fillets groups, while some differences were found in the cooked fillets groups. Except for the values of "favorite", the sensory evaluation of the muscle did not reveal significant differences among the PFM, SFM, APB60 and APB80 groups. Fish fed the PFM and SFM diets exhibited normal liver histological structure. However, high levels of substitution of PFM by APB might induce hepatic steatosis for this species. However, the adverse effects cannot be ignored when the total PFM is replaced by SFM. (C) 2012 Elsevier B. V. All rights reserved.