Fish meal replacement by soy protein from soymilk in the diets of red sea bream (<i>Pagrus major</i>)

Abstract

Six isoenergetic diets were formulated as follows: fish meal (FM) 700 g kg–1 (control, C), FM 300 g kg–1 + soy protein concentrate 300 g kg–1 (SPC), FM 300 g kg–1 + enzyme-treated SPC 300 g kg–1 (ESC), FM 170 g kg–1 + soy protein isolate 300 g kg–1 (SPI), FM 160 g kg–1 + enzyme-treated SPI 300 g kg–1 (ESI) and FM 150 g kg–1 + conglycinin 300 g kg–1(CG). Forty fish (3.9 g) were randomly distributed into each of eighteen 300-L tanks, fed twice daily until satiation for 8 weeks. The final body weight, specific growth rate and condition factor did not show significant differences among the fish fed with diets C, SPC, ESC and ESI (p > .05). The survival was significantly lower in fish fed with diets SPI and CG. Feed efficiency was significantly higher in fish fed with diets SPC and C than in fish fed with other diets (p < .05). There were no significant differences in nutrients retention efficiencies in fish fed with diets C, SPC, ESC and ESI. A significantly higher phosphorus retention efficiency in fish fed with soymilk protein diets resulted in lower phosphorus discharge to the environment (p < .05). These results suggest that the soymilk proteins can comfortably replace 570–770 g FM kg–1 diet of red sea bream juvenile, which will ensure significant ecological benefits through reducing phosphorus load to the environment.