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

Six isoenergetic diets were formulated as follows: fish meal (FM) 700gkg(-1) (control, C), FM 300gkg(-1) + soy protein concentrate 300gkg(-1) (SPC), FM 300gkg(-1) + enzyme-treated SPC 300gkg(-1) (ESC), FM 170gkg(-1) + soy protein isolate 300gkg(-1) (SPI), FM 160gkg(-1) + enzyme-treated SPI 300gkg(-1) (ESI) and FM 150gkg(-1) + conglycinin 300gkg(-1)(CG). Forty fish (3.9g) were randomly distributed into each of eighteen 300-L tanks, fed twice daily until satiation for 8weeks. 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 570-770gFMkg(-1) diet of red sea bream juvenile, which will ensure significant ecological benefits through reducing phosphorus load to the environment.