Partial replacement of fish meal by soy protein concentrates in diets for a new Japanese strain of juvenile soft-shelled turtle,Pelodiscus sinensis

Abstract

An 8-week experiment was conducted to evaluate the effects of dietary fish meal (FM) replaced by soybean protein concentrate (SPC) on Japanese strain of soft-shelled turtle, Pelodiscus sinensis juveniles. Diets were formulated to replace FM protein by SPC at 0, 15, 30, 45, 60 or 60% supplemented with phytase (2000 FTU kg−1) (designated as S0, S15, S30, S45, S60 and S60P, respectively), and each diet was fed to triplicate groups. The results showed that the growth was significantly lower when dietary SPC replaced more than 45% FM. The turtles fed the S15 or S30 diet showed comparable feed and protein utilization efficiency compared with the S0 group, whereas more than 30% replacement of FM adversely affected these values. Increasing dietary SPC levels significantly lowered the apparent digestibility coefficients (ADC) of dry matter, protein, lipid, phosphorus and gross energy. Whole-body protein, ash and phosphorus content showed a declining trend when dietary SPC levels increased, while body lipid and moisture content were unaffected. When the turtles were fed diets with increasing levels of SPC, serum total protein concentration, alkaline phosphatase and catalase activities decreased with a corresponding increase in glutamic pyruvic transaminase activity. Turtles fed the S60P diet showed comparable growth performance and feed utilization efficiency to the S40 group, and were superior to the S60 group. The present study showed that SPC could successfully substitute for 30% FM protein in the diets for P. sinensis juveniles, and the maximum effective substitution may be greater if exogenous phytase was added.