Effects of Stocking Density on Growth, Hepatic Antioxidant and Inflammatory Responses, and Intestinal Barrier Function in Cage-Cultured Large Yellow Croaker (Larimichthys crocea)

This study investigated the effects of stocking density on growth, antioxidant responses, hepatic inflammatory signaling, and intestinal barrier function in cage-cultured large yellow croaker (Larimichthys crocea). Fish (~288 g) were reared for 8 weeks at low (5.73 kg/m3), medium (8.64 kg/m3), or high (11.55 kg/m3) initial stocking densities. High density reduced growth and survival and increased feed conversion ratio, serum cortisol, glucose, and malondialdehyde, while decreasing total antioxidant capacity and superoxide dismutase activity (p < 0.05). Hepatic Nrf2, SOD, CAT, and GPX expression decreased, whereas Keap1 expression increased at high density. High density also increased pro-inflammatory cytokine expression and NF-κB p65 phosphorylation, decreased anti-inflammatory factors and IκB abundance, shortened intestinal villi, reduced ZO-1, Occludin, and Claudin-1 abundance, and increased serum diamine oxidase, D-lactate, and endotoxin (p < 0.05). Medium-density fish showed generally comparable responses to low-density fish for most endpoints. These findings indicate that high stocking density induces physiological stress and oxidative imbalance associated with an impaired hepatic Nrf2-related antioxidant response, enhanced NF-κB inflammatory signaling, and impaired intestinal barrier integrity in large yellow croaker.