A 5-week feeding trial was conducted to examine the effect of γ-ray irradiation on the inclusion of soybean meal (SBM) and soy protein concentrate (SPC) in diets of juvenile golden pompano (Trachinotus ovatus). One diet containing 320 g kg−1 fish meal served as a reference (C), and another four diets were formulated with 75% of the fish meal replaced by SBM, SPC, SBM irradiated with γ-ray at 30 kGy (SBM30) or SPC irradiated with γ-ray at 30 kGy (SPC30).

Results indicated that the weight gain was higher in fish fed diets SBM30 and SPC30 compared to the fish fed diets SBM and SPC. No significant differences were found in feed conversion ratio, nitrogen retention efficiency, phosphorus retention efficiency, condition factor, hepatosomatic index, body composition, waste outputs of nitrogen and phosphorus either between fish fed diets SBM and SBM30 or between fish fed diets SPC and SPC30. No significant differences were found in nitrogen retention, condition factor, hepatosomatic index and body composition (i.e. moisture, crude protein, crude lipid and ash) between fish fed the control diets and those fed the irradiated protein sources. The macromolecular proteins in SBM and SPC were degraded, whereas the contents of peptides with molecular weight ‹6.5 kDa were increased by γ-ray irradiation. This study reveals that γ-ray irradiation can improve the performance of SBM and SPC as a fish meal substitute in the golden pompano diet.