Use of fermented fisheries by-products and soybean curd residues mixture as a fish meal replacer in diets of juvenile olive flounder, Paralichthys olivaceus

A 10-wk feeding trial was conducted to evaluate the potential use of fermented fisheries by-products and soybean curd residues mixture (FFSM) as a partial replacement for fish meal (FM) in the diet of juvenile olive flounder, Paralichthys olivaceus. Five experimental diets were formulated with FFSM replacing 0, 15, 30, 45, and 60% of the FM protein (FFSM0, FFSM15, FFSM30, FFSM45, and FFSM60, respectively). Juvenile olive flounder averaging 5.99 +/- 0.08 g (mean +/- SD) were randomly distributed into aquaria at 15 fish/aquarium, with three replicate aquaria for each experimental diet. Weight gain (WG) of fish fed FFSM0, FFSM15, and FFSM30 was significantly higher than that of fish fed FFSM45 and FFSM60 (P < 0.05). Also, WG of fish fed FFSM45 was significantly higher than that of fish fed FFSM60 (P < 0.05). There were no significant differences in WG among fish fed FFSM0, FFSM15, and FFSM30 (P > 0.05). Specific growth rate (SGR) of fish fed FFSM15 was significantly higher than that of fish fed FFSM45 and FFSM60 (P < 0.05). Also, SGR of fish fed FFSM0, FFSM15, FFSM30, and FFSM45 was significantly higher than that of fish fed FFSM60 (P < 0.05). There were no significant differences in SGR among fish fed FFSM0, FFSM15, and FFSM30 and among those fed FFSM0, FFSM30, and FFSM45 (P > 0.05). Feed efficiency (FE) and protein efficiency ratio (PER) of fish fed FFSM60 were significantly lower than those of fish fed FFSM0, FFSM15, FFSM30, and FFSM45 (P < 0.05); however, there were no significant differences in FE and PER among fish fed FFSM0, FFSM15, FFSM30, and FFSM45. Hepatosomatic index of fish fed FFSM0, FFSM15, and FFSM30 was significantly higher than that of fish fed FFSM60 (P < 0.05); however, there were no significant differences among fish fed FFSM0, FFSM15, FFSM30, and FFSM45 and among those fed FFSM45 and FFSM60. No significant differences were observed in condition factor and survival rate among all dietary groups tested. The whole-body proximate composition averaged 75.0 (% dry matter basis [DM]), 8.66 (% DM), 16.38 (% DM), and 76.1%, for crude protein, crude lipid, ash, and moisture, respectively. Based on growth performance, the FFSM could replace up to 30% FM protein by the ANOVA test; however, broken-line model analysis indicated 28.7% as an optimum replacement level in juvenile olive flounder diets.