Replacement of fish meal with gamma‐ray irradiated soybean meal in the diets of largemouth bass Micropterus salmoides

Abstract

This study evaluates the potential to replace fish meal with gamma-ray (γ) irradiated soybean meal (SM) in the diet of largemouth bass (Micropterus salmoides) and the role of brewer's yeast (Saccharomyces cerevisiae) supplementation in fish meal replacement. The reference diet (490 g kg−1 crude protein, 90 g kg−1 lipid and 400 g kg−1 fish meal) was formulated into six isoproteic and isolipidic experimental diets. In the first three diets (S20, S40 and S60), 20%, 40% and 60% of fish meal in the reference diet was replaced with γ-irradiated SM, respectively. The brewer's yeast was then supplemented to diets S20, S40 and S60 at 10 g kg−1 to form other three diets (SY20, SY40 and SY60). The feeding trial lasted 8 weeks. Fish weight gain was not affected by the level of fish meal replacement, yeast supplementation and their interactions. Fish meal replacement and yeast supplementation significantly affected feed intake, feed conversion ratio (FCR), retention efficiencies of nitrogen (NRE) and phosphorus (NRE), nitrogen waste, phosphorus waste and the ratio of fish meal consumption to fish production (RCP). The hepatosomatic index and body contents of moisture and lipid were dependent on the level of fish meal replacement. The contents of protein, ash and phosphorus in the whole body depended on fish meal replacement and the interaction between fish meal replacement and yeast supplementation. No significant difference was found in weight gain between fish fed the reference diet and six experimental diets. Feed intake and FCR were lower in fish fed the reference diet than those fed diets S20, S40, S60, SY20 and SY60. However, feed intake, FCR, NRE and nitrogen waste in fish fed diet SY40 did not differ from those fed the reference diet. The RCP declined with the decrease of dietary fish meal. This study indicates that the γ-irradiated SM is a promising ingredient as a fish meal substitute. Fish meal can be reduced to 160 g kg−1 with γ-irradiated SM as the substitute in the largemouth bass diet. The supplementation of S. cerevisiae at 10 g kg−1 did not show a positive role for the reduction of fish meal in the largemouth bass diet.