Effects of replacement of fish meal by poultry by-product meal on growth performance and gene expression involved in protein metabolism for juvenile black sea bream (Acanthoparus schlegelii)

An 8-week feeding trial was conducted to evaluate the effects of replacement of fish meal (FM) with poultry by-product meal (PBM) on growth performance, feed utilization and expression of genes involved in protein metabolism in juvenile black sea bream (Acanthoparus schlegelii). Six isonitrogenous (42%) and isolipidic (11%) experimental diets were formulated to replace 0% (control diet), 10%, 20%, 30%, 40% and 60% protein from FM with PBM. All the diets except the control diet were supplemented with lysine and methionine to keep same lysine and methionine levels among all diets. A total of 360 fish (approximately initial weight, 0.46 +/- 0.02 g) were randomly stocked and sorted in 18,300-L cylindrical fiberglass tanks, each diet was randomly assigned to triplicate groups of 20 juvenile black sea bream and fed twice each day to apparent satiation. The results showed that survival ranged from 88.33 to 93.33%, and there were no significant differences among all treatments (p > .05). Final body weight (FBW) and percent weight gain (PWG) significantly increased with dietary replacement levels of FM with PBM increasing from 0% to 30%, and significantly decreased when replacement of FM with PBM further increased from 30% to 60% (p < .05), fish fed the 30% replacement of FM with PBM diet had higher FBW and PWG than those fed the other diets. Based on PWG against replacement levels of FM with PBM, A two-slope broken-line model analysis indicated that the optimal replacement of FM with FBM is to be 28.30%. Proximate composition in whole body did not show significant differences among all dietary treatments (p > .05). Higher hepatosomatic index (HSI) was observed in fish fed the 30% replacement of FM with PBM compared to the control and other diets, however, viscerosomatic index (VSI) and condition factor (CF) were not significantly influenced by the replacement of FM with PBM(p > .05). Fish fed the diet containing 30% replacement of FM with PBM had higher lysine and methionine concentration in muscles than those fed the other diets, however, other essential or non-essential amino acids in muscle were not significantly affected by dietary replacement of FM with PBM. The relative expressions of igf1, tor, s6k1, pi3k and akt were significantly upregulated when replacement levels of FM with PBM increased from 0% to 30%, however, the expression levels of these genes significantly down-regulated with the further increase of replacement level of FM by PBM (p < .05). Moreover, the lowest expression of 4e-bp2 was occurred at fish fed the 30% replacement of FM with PBM among all treatments. In summary, the results of present study indicated that dietary PBM supplementation could be an alternative protein source for black sea bream, and 30% replacement of FM with PBM could improve growth and up-regulate the relative expression of genes involved in protein metabolism.