|Rawles, Steven - Steve|
Submitted to: Aquaculture Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/6/2010
Publication Date: 6/1/2011
Citation: Rawles, S.D., Thompson, K.R., Brady, Y.J., Metts, L.S., Aksoy, M., Gannam, A.L., Twibell, R.G., Ostrand, S., Webster, C.D. 2011. Effects of feed grade poultry by-product meal, soybean meal and protein level in the diet on the performance and immune status of pond-grown sunshine bass (Morone chrysops X M. saxatilis). Aquaculture Nutrition. 17:e708-e721. Interpretive Summary: Fish meal is an expensive and unsustainable ingredient in fish feeds. Two ways to lower the cost of hybrid striped bass feeds are to replace fish meal and to reduce the level of protein in the diet. A long term feeding trial was conducted to evaluate the performance, health, and fillet quality of hybrid striped bass that were fed diets containing 40% protein based on poultry by-product plus methionine (an essential amino acid) in comparison to fish fed a typical fishmeal-based diet. We also experimented with lowering the protein level in the poultry based diet from 40% to 36% and 32%. The diets were extruded by a commercial feed mill with practical ingredients to mimic industry feeds. The feeding trial was conducted in ponds stocked at commercial densities. At harvest, there were no differences between fish fed the diet containing fish meal and those fed the poultry by-product meal + methionine diet when both diets contained 40% protein. However, when diet protein was decreased below 40% in the poultry based diets, growth, meat quality and fish health status also declined. In addition, the number of marketable fish greater than 1.5 lbs decreased and the amount of smaller fish commanding a lower price increased when diet protein was reduced below 40%. Therefore, it should be possible now to completely replace fish meal with poultry by-product and supplemental methionine in current hybrid striped bass diets containing 40% protein. However, more work is needed in order to safely replace fish meal while reducing protein level at the same in commercial hybrid striped bass diets.
Technical Abstract: Two primary ways to achieve low-cost, nutritionally efficacious diets for sunshine bass (Morone chrysops X M. saxatilis) are to decrease crude protein levels and use alternative animal or plant ingredients to partially, or totally, replace fish meal. A 459-day feeding trial was conducted with juvenile (35g) 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 40% 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 (P > 0.10) differences were found in feed intake and feed conversion ratio. The 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 5.6% to 6.2%, 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 with judicious amino acid supplementation of this product appear promising.