Reducing dietary protein in pond production of hybrid striped bass (Morone chrysops × M. saxatilis): Effects on fish performance and water quality dynamics
Abstract In previous work, we demonstrated that diets containing 40% digestible protein (DP) (45% crude protein) and 18% lipid supplemented with Met and Lys resulted in superior performance and nutrient retentions in hybrid striped bass (HSB) compared to less energy-dense diets when rearing HSB at temperatures similar to the summer growing period of the Southern U.S. The current work was aimed at vetting previous results in pond production of market-size HSB at commercial stocking densities to assess impacts on fish production indices and water quality parameters. Diets were formulated to contain digestible protein levels ranging from 41% to 35% DP and 15% crude lipid. The trial was conducted during the hottest portion of the growing season when impacts of feeding have the greatest influence on pond water quality. The 6-month pond (0.1 ha; 0.25 ac) study began with advanced juveniles (121.4 ± 3.21 g/fish; mean ± SD) in May 2013 and concluded with market sized fish in October 2013. Final fish size ranged from 448 ± 24 g to 1122 ± 46 g with food conversions ranging from 1.34–1.37. Results suggest that DP can be lowered from 41% DP to 35% DP by careful diet formulation while supplementing the first three limiting amino acids (Met, Lys Thr) without detrimental changes to body composition or nutrient retentions. Market size distributions, nutrient retention, and pond water quality dynamics in relation to test diets are also discussed.