Evaluation of poultry by-product meal in commercial diets for hybrid striped bass (Morone chrysops ♀ × M. saxatilis ♂) in recirculated tank production

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 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 and 70PBM, 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·day− 1 divided into morning and evening feedings and gradually decreased to 1.5% body weight·day− 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) performed as well as fish fed the generic diet, whereas fish fed the 70PBM 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.