Improvement of fish meal replacements by soybean meal and soy protein concentrate in golden pompano diet through γ-ray irradiation

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 (SM), SPC (SC), SBM irradiated with γ-ray at 30 kGy (SM30) or SPC irradiated with γ-ray at 30 kGy (SC30). The weight gain was higher in fish fed diets SM30 and SC30 than in fish fed diets SM and SC, respectively, whereas fish consumed more diet SM30 than diets SM, SC or SC30. No significant differences were found in feed conversion ratio, nitrogen retention efficiency (NRE), phosphorus retention efficiency (PRE), condition factor, hepatosomatic index (HSI), body composition, waste outputs of nitrogen (NWO) and phosphorus (PWO) either between fish fed diets SM and SM30 or between fish fed diets SC and SC30. The weight gain and PWO were higher, but the PRE and the body phosphorus content were lower in fish fed diet C than those in fish fed diets SM30 or SC30. No significant differences were found in the NRE, condition factor, HSI and body composition (i.e. moisture, crude protein, crude lipid and ash) between fish fed diets C and SM30 or between fish fed diets C and SC30. 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.