Effects of replacing fish meal with poultry by-product meal and soybean meal and reduced protein level on the performance and immune status of pond-grown sunshine bass (Morone chrysops × M. saxatilis)

Two primary ways to achieve low-cost, nutritionally efficacious diets for sunshine bass (Morone chrysops × M. saxatilis) are to decrease crude protein (CP) levels and the use alternative animal or plant ingredients to partially, or totally, replace fish meal. A 459-day feeding trial was conducted with juvenile (35 g) sunshine bass to evaluate growth, feed efficiency, size distribution at harvest, immune function status and body composition when fed diets containing soybean meal (SBM), feed-grade poultry by-product meal (PBM), and supplemental methionine as complete replacements for menhaden fish meal (MFM) at 300 g kg−1 diet, while simultaneously reducing dietary crude protein (CP; 320, 360, and 400 g kg−1). The feeding trial was conducted in 12, 0.04-ha earthen ponds stocked at a rate of 300 per pond (3000/ac). At 400 g kg−1 dietary protein, there were no differences in responses between fish fed the diet containing MFM or the diet in which MFM was completely replaced with PBM and supplemental methionine on a digestible protein basis. However, final mean weight, percentage weight gain, specific growth rate, and protein efficiency ratio were linearly related (P < 0.10) to dietary protein level in the diets while no significant differences were found in feed intake and feed conversion ratio. The expected odds of fish at harvest being classified into larger size categories (> 680 g) decreased as dietary protein level decreased based on ordinal logistic regression. There were no significant relationships between body compositional indices and dietary treatments. Body fat ranged from 56 g kg−1 to 62 g kg−1, single fillets ranged from 28% to 30%, and livers ranged from 2.45% to 2.62% of body weight across treatments. Fillet protein concentration was positively linear and quadratic for protein level in the diet but fillet moisture, lipid and ash did not differ among diets. Total serum protein, immunoglobulin and lysozyme activity decreased linearly with decreasing diet protein level. These results suggest that complete replacement of MFM with feed grade PBM and supplemental methionine is possible in diets for sunshine bass and that further reductions in dietary protein level may be possible with amino acid supplementation.