Walleye Sander vitreus performance, water quality, and waste production in replicated recirculation aquaculture systems when feeding a low phosphorus diet without fishmeal versus a traditional fishmeal-based diet

Abstract Walleye Sander vitreus is a popular sport- and food-fish in areas surrounding the Great Lakes. Walleye are mainly provided as food-fish by limited capture fisheries, but have potential for profitable production to market-size in recirculation aquaculture systems (RAS). Walleye are piscivorous with a supposed requirement for fishmeal in artificial diets, thus little information is available regarding the effects of feeding fishmeal-free diets to walleye. During this study, the health and growth performance of juvenile walleye cultured in RAS were compared between groups fed either a traditional fishmeal-based diet (FM) or a low phosphorous, fishmeal-free (FMF) diet. Water quality and waste production rates resulting from feeding each diet were evaluated. The FM diet contained fishmeal, poultry meal, soybean meal, wheat flour, and blood meal proteins; and the FMF diet used poultry meal, wheat flour, soy protein concentrate, and corn protein concentrate proteins. The only lipid source used in the FM diet was fish oil from menhaden, whereas the FMF diet used menhaden oil and poultry oil. Each diet was formulated with a protein: fat ratio of approximately 42/18. Fish (initial weight 85 g fish −1 ) were cultured in 6 replicated RAS for 9 months, each operated with 99.9% water recycle on a flow basis, a mean system hydraulic retention time of 135 days, and a mean feed loading rate of 3.5 kg feed/m 3 of daily makeup water. At study’s end, mean weights ± standard error of fish fed the FM and FMF diets were 571 ± 26 and 589 ± 15 g, respectively ( P  > 0.05). Cumulative survival for both diet treatments was ≥98.5%. Average thermal growth coefficient (TGC), condition factor (CF), and feed conversion ratio (FCR) were similar ( P  > 0.05) for the FM and FMF diets, respectively: TGC was 0.82 ± 0.01 and 0.83 ± 0.02; CF was 1.05 ± 0.02 and 1.03 ± 0.02; and FCR was 1.32 ± 0.02 and 1.27 ± 0.03. Water color index and UV transmittance values ( P P P  > 0.05). Whole-body and fillet proximate composition was similar between treatments; however, gonadosomatic index and the ratio of omega 6: 3 fatty acids was greater ( P