Optimum fish meal replacement by soy protein concentrate from soymilk and phytase supplementation in diet of red sea bream, Pagrus major

Two trials were carried out to determine the optimal replacement level of fish meal (FM) by soy protein concentrate (SPC) derived from soymilk without supplementation of indispensable amino acids (IAAs) or palatability enhancers and whether phytase supplementation can help to replace more SPC in diet of juvenile red sea bream, Pagrus major. In Trial 1, five isoenergetic diets were formulated: 67% FM as protein source in the control diet (C), and FM was replaced by 60 (SPC60), 70 (SPC70), 80 (SPC80) and 100% (SPC100) by SPC. In Trial 2, diets C and SPC80 were the same as in Trial 1, and phytase was supplemented in SPC80 at 1000 (P1), 2000 (P2), 3000 (P3) and 4000 (P4) FTU/kg diet. Thirty (ca. 23 g) and 20 fish (ca. 21 g) were randomly distributed into each fifteen and eighteen 300 L indoor tanks in Trial 1 and 2, respectively. Fish in both trials were fed two times daily until apparent satiation for 10 weeks. At the end of both trials, feces were collected after feeding with chromic oxide (Cr2O3) mixed diets. In Trial 1, there were no significant differences in final mean weight, specific growth rate (SGR), daily feeding rate (DFR), feed efficiency (FE), condition factor (CF), and retention efficiency of protein, lipid and energy until 70% (SPC70) FM replacement by SPC (P > .05). However, 80% FM replacement significantly reduced final mean weight, FE and lipid retention efficiency compared with group C (P < .05). There were no significant differences in plasma constituents, except total cholesterol level. In Trial 2, phytase was supplemented in SPC80 to determine whether it helps to stimulate growth up to the level of the control group. Fish fed SPC80 once again displayed significantly lower final mean weight, SGR, FE, phosphorus (P) digestibility, and retention efficiency of protein, lipid, energy and P compared with control group (P > .05). Final mean weight, FE, P digestibility, and retention efficiency of protein, lipid and P were significantly improved in fish fed diet P2 (phytase at 2000 FTU/kg diet) compared with those fed diet SPC80. However, phytase supplementation did not stimulate the growth up to the level of group C. The results demonstrated in juvenile red sea bream that 70% of FM can be replaced by SPC derived from soymilk without supplementation of IAAs and palatability enhancers.