Impact of stocking density on growth performance, hematology and serum biochemistry of catfish (Pangasianodon hypophthalmus) cultured in in-pond raceway system

Optimizing rearing density and defining physiological thresholds is critical for maximizing the economic viability and welfare of intensive land-based aquaculture systems. This study evaluated biomass dynamics and physiological responses of striped catfish (Pangasianodon hypophthalmus) in an in-pond raceway system (IPRS). Fish (initial weight: 23.62 ± 2.42 g) were stocked at three densities: SD1 (8,000 fish; 0.71 kg/m³), SD2 (11,000 fish; 0.98 kg/m³), and SD3 (14,000 fish; 1.25 kg/m³), with final harvest densities reaching 24.24, 31.75, and 38.51 kg/m³, respectively. Growth performance (FBW, WG, SGR) was significantly higher in SD1 (P < 0.05). Notably, FCR was significantly better in SD1 (1.21) and SD3 (1.30) than SD2 (1.41), indicating a transition from territorial aggression to passive shoaling at extreme densities. Hematology (RBC, Hb, Hct) and serum enzymes (ALT, AST, ALP) increased progressively with stocking density, with the most pronounced elevations recorded at SD3 (38.51 kg/m³; P < 0.05), demonstrating that, as a refined outcome of our a-priori threshold hypothesis, physiological stress was progressive and dose-dependent across the evaluated density range rather than defined by a single discrete break-point. These results provide commercial farmers with actionable benchmarks for optimizing loading densities in IPRS to maximize production while ensuring fish health and welfare.