Density and feeding regulation of largemouth bass (Micropterus salmoides) in a streamlined recirculating aquaculture system: Implications for growth performance and physiological stability

Streamlined recirculating aquaculture systems (sRAS) have been proposed as economically efficient alternatives to conventional recirculating systems for intensive freshwater aquaculture. However, key management parameters in sRAS remain insufficiently defined from a biological perspective. Using largemouth bass ( Micropterus salmoides ) as a representative carnivorous species, this study examined how stocking density and feeding frequency jointly influence growth performance, physiological condition, and flesh quality under sRAS conditions, with the objective of identifying production-relevant management strategies. Fish were reared for 180 days under a 3 × 3 factorial design combining three stocking densities (60, 100, and 140 fish m⁻³) and three feeding frequencies (2, 3, and 4 times day⁻¹). Growth performance, body indices, muscle texture properties, serum biochemical variables, hepatic antioxidant status, and intestinal digestive enzyme activities were evaluated. High stocking density (140 fish m⁻³) consistently impaired growth performance and was associated with elevated metabolic demand and oxidative stress, indicating that biological constraints persist even under optimized hydrodynamic and oxygenation conditions. Feeding frequency modified these responses but did not offset the negative effects imposed by high stocking density, indicating that biological constraints associated with density remained the primary driver of physiological stress under sRAS conditions. While higher feeding frequency stimulated digestive enzyme activity, it was accompanied by increased oxidative stress and did not yield proportional gains in growth or flesh quality. In contrast, a feeding frequency of three times per day supported a more balanced physiological state across density treatments. Taken together, the results suggest that maintaining a moderate stocking density (60–100 fish m⁻³) in combination with three daily feedings provides a stable compromise between growth efficiency, physiological regulation, and product quality in closed-loop sRAS. These findings offer practical guidance for density–feeding management in simplified recirculating systems and contribute to their application in intensive freshwater aquaculture.