White trevally (Pseudocaranx dentex ) is a novel marine finfish aquaculture species with a high market value that is being cultured commercially in Japan. Aquaculture nutrition research of white trevally has been little explored for the optimization of juveniles. This research evaluates the potential of soybean meal (SBM) as a replacement of fish meal (FM ) and poultry byproduct meal (PBM) as a replacement for the flavor attractant krill meal (KM) in an effort to develop an environmentally sustainable and cost-effective juvenile diet for white trevally.
Three feeding trials were carried out at the Uragami Station, Aquaculture Research Institute of Kindai University, Japan . In trial 1, six iso-energetic diets were formulated; FM 560 g kg-1 diet (Control, diet C), and FM protein in diet C was replaced at 10 (S-10) , 20 (S-20) , 30 (S-30), 40 (S- 40) and 50% (S-50) by SBM , and compared to a commercial reference . Fifteen juveniles (mean weight, ca. 42.7g) were randomly distributed into each of twenty-one 500L tanks , set in triplicate and fed twice daily until apparent satiation for 10 weeks . To further determine the optimal level of FM replacement by SBM in relatively small fish, in trial 2 seven iso-energetic diets were formulated, and FM protein was replaced at 30 (S-30) , 35 (S-35), 40 (S-40), 45 (S- 45) and 50% (S- 50) by SBM . Another diet was designed by omitting binders carboxymethyl cellulose and guar gum from diet C, and referred to as C-CG. Thirty juveniles (mean weight, ca. 3.68g) were randomly distributed into each of twenty-one 300L tanks , set in triplicate and fed twice daily until apparent satiation for 6 weeks . In t rial 3, diet C-CG from t rial 2 was used as the control. An additional five iso-energetic diets were formulated as follows: FM protein from diet C-CG was replaced at 50 (S-50) and 70% (S-70) and KM from diets S-50 and S-70 was replaced by PBM and subsequently referred to as P-50 and P- 70, respectively, and a FM-free diet (FMF). Fifteen juveniles (mean weight, ca. 31.8g) were randomly distributed into eighteen 500L tanks , set in triplicate and fed twice daily until apparent satiation for 8 weeks .
In trial 1, all SBM-based diets outperformed the control and commercial reference diets in terms of final weight gain and feed efficiency. The results of trial 2 revealed no significant differences between diets C and C-CG, indicating that binder was not the cause of poor growth performance of diet C in t rial 1. Although there were no significant differences among SBM-based diets (P>0.05), S- 50 exhibited the greatest final weight gain out of all treatments. In t rial 3, there were no significant differences in the growth performance among SBM-based diets (P>0.05) . While there were no statistical differences between diets C-CG and FMF, fish fed with diet S- 70 showed significantly higher growth performance than those fed with both diets (P<0.05). The results of trials 1, 2 and 3 indicate that SBM has the ability to effectively replace FM up to 7 0% with the addition of KM, methionine, lysine, taurine and phytase supplementation. In addition, PBM has the ability to effectively replace KM i n up to 50% FM replacement diets by SBM.