|Rawles, Steven - Steve|
Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2006
Publication Date: 9/8/2006
Citation: Rawles, S.D., Riche, M.A., Gaylord, T.G., Webb, J., Freeman, D.W., Davis, M. 2006. Evaluation of poultry by-product meal in commercial diets for hybrid striped bass (Morone chrysops x M. saxatilis) in recirculated tank production. Aquaculture. 259:377-389. Interpretive Summary: Current aquaculture diets require fishmeal as a major protein source. Fishmeal is a limited resource with competitive markets in the animal feed industry. We tested commercial diets for hybrid striped bass (HSB) in which fishmeal was replaced by petfood grade poultry by-product (PBM). The commercial test diets were evaluated under production conditions in a commercial-scale recirculating tank system. We used the “ideal protein” approach to formulate a typical generic production diet for HSB. In this approach, amino acids—the building blocks of protein—are added to the diet to match levels found in the muscle of fish. The idea is that levels of amino acids found in the meat will mimic the nutritional requirements of the fish. Two critical amino acids, methionine and lysine, were added to the diets in this way. We then replaced 35% or 70% of the fishmeal in the generic diet with PBM. The diets were formulated with ingredients typically used by the fish farming industry and manufactured by a commercial feed mill. HSB were fed at a constant amount of food twice each day for 24 weeks. At the end of the trial we found that final fish weight, weight gain, total harvest per tank, liver size (an indicator of health) and body fat were significantly different in fish fed the different diets. Generally, fish fed the 35% replacement diet performed as well as fish fed the generic diet. However, fish fed the 70% replacement diet performed more poorly. Significant differences between the formulated and digestible levels of two or more critical amino acids in the 70% replacement diet probably caused the poorer performance of this diet. However, since the generic diet already contained some poultry by-product these results clearly demonstrate that poultry by-product can successfully replace nearly half of the protein from fishmeal in commercial HSB diets when critical amino acids are added to the diet. Even with the cost of adding the missing amino acids, these results should reduce the cost of HSB diets and spare fishmeal - a limited resource.
Technical Abstract: The efficacy of replacing fishmeal with petfood grade poultry by-product (PBM) on an ideal protein basis in commercial diets for hybrid striped bass (HSB) was evaluated under production conditions in recirculated tank culture. A generic production diet (GEN) for HSB was formulated to contain 45% protein, 12% lipid and 3.7 kcal/kg. Protein in the generic diet was supplied by a mix of animal and plant sources typically used by the industry that included more than 20% select menhaden fishmeal and less than 10% PBM. A positive control diet (GEN+AA) was formulated by supplementing the generic diet with feed-grade Met and Lys to match the level of those amino acids in HSB muscle at 40% digestible protein. Substitution diets were formulated by replacing 35% or 70% of fishmeal in the GEN diet with PBM on a digestible protein basis and then supplementing with Met and Lys (designated 35PBM+AA and 70PBM+AA, respectively) as needed to maintain concentrations of Met and Lys equal to those in the GEN+AA diet. Diet formulation and extrusion were conducted by a commercial mill. Fish were stocked (87 g average initial weight) in three replicated production-scale recirculating culture systems. Diets were initially fed at 4% body weight•d-1 divided into morning and evening feedings and gradually decreased to 1.5% body weight•d-1 during the 24-week trial. The availability of indispensable amino acids (IAA) in the commercial test diets were determined in a separate trial. All test diets were replete with respect to published requirements of hybrid striped bass; however, available levels of Arg and Thr were first- and second-limiting, respectively, and His was third-limiting, in the replacement diets when compared to the IAA profile of hybrid striped bass muscle. Diet composition significantly (P < 0.05) influenced final weight, weight gain, yield, hepatosomatic index (HSI) and intraperitoneal fat (IPF) ratio, but did not significantly alter feed conversion and muscle ratio. Generally, fish fed the 35% replacement diet (35PBM+AA) performed as well as fish fed the generic diet, whereas fish fed the 70PBM+AA diet not. Fish fed the supplemented generic diet (GEN+AA) outperformed fish fed the other test diets. Results clearly demonstrate that formulation on an available amino acid basis can significantly improve the performance of current diets for HSB and that petfood grade poultry by-product can successfully provide nearly half the protein in commercial HSB diets when substituted for fishmeal on an available amino acid basis. These results should reduce the cost of commercial HSB diets and spare fishmeal - a limited resource.