Partial replacement of fishmeal by a protein‐rich product from methanotrophic bacteria in juvenile red sea bream ( Pagrus major )

Abstract

The optimum level of fishmeal (FM) protein replacement by bacterial protein meal (BPM) was determined in the diet of juvenile red sea bream, Pagrus major. Six isoproteic and isolipidic diets were formulated to replace 0 (control diet), 190 , 280, 370, 470 and 560 g of the FM protein kg-1 diet with BPM protein, and referred to as C, BP19, BP28, BP37, BP47 and BP56, respectively. Each diet was fed to triplicate groups of twenty fish (mean weight ~43 g) twice per day to apparent satiation. Fish fed diets C and BP19 did not show significant differences (p > .05) in growth, apparent digestibility or protein and lipid retention efficiency, but the daily feeding rate (DFR) was significantly lower under BP19 than under C. However, almost all growth parameters were significantly reduced when FM protein replacement with BPM was further increased from 280 to 560 g kg-1 diet (p < .05). The results of polynomial regression analysis (second-order) revealed significant negative correlations between dietary copper levels and final mean weight (R2 = .913), specific growth rate (R2 = .913) and DFR (R2 = .956). The results indicated that BPM could replace approximately 190 g of FM protein kg-1 diet in the juvenile red sea bream diet without compromising growth performance or feed efficiency.