Physiological responses of channel catfish (Ictalurus punctatus) reared at different stocking densities in a recirculating aquaculture system

Abstract

This study investigated the physiological responses of channel catfish (Ictalurus punctatus) reared under different stocking densities (SDs). Juvenile channel catfish with an average initial body weight of 40.6 ± 2.23 g were reared at three densities of 2.03 (low SD; LSD), 6.09 (medium SD; MSD), and 12.18 (high SD; HSD) kg m−3 for 60 days. Serum biochemistry, antioxidant defense status, immune parameters, and hepatic heat shock proteins (hsps) mRNA expression were analyzed. Serum cortisol levels are significantly elevated in MSD and HSD. A significant increase in lysozyme (LZM) activity and the contents of immunoglobulin M (IgM) and complement component 3 (C3) were observed with the increased SD. Total antioxidant capacity (T-AOC) and the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) did not significantly affect SD. I. punctatus reared in HSD showed significantly increased catalase (CAT) activity, malonaldehyde (MDA) content, and nitric oxide (NO) levels. Hepatic hsp70 and hsp90 mRNA expression were significantly downregulated in HSD compared to LSD. Overall, HSD caused chronic stress in I. punctatus, leading to biochemical and immune function variations