Influence of stocking ratios on production and stress indicators in <i>Channa striata</i> and <i>Heteropneustes fossilis</i> polyculture systems

This study investigated the effects of different stocking ratios on growth performance, physiological responses, and injury patterns in co-reared Channa striata and Heteropneustes fossilis . A 56-day experiment employed three treatment groups: T1 (1:1 ratio; 50% C. striata : 50% H. fossilis ), T2 (3:7 ratio; 30% C. striata : 70% H. fossilis ), and T3 (7:3 ratio; 70% C. striata : 30% H. fossilis ), each with three replicates. Nine concrete tanks filled with dechlorinated water, each containing 30 fish per tank (initial weight of C. striata : 15.3 ± 0.4 g; H. fossilis : 15.1 ± 0.5 g), were maintained under natural photoperiod and temperature conditions (18−25°C). Fish were fed commercial feed (40.2% protein) at 5% body weight daily. Samples collected on days 1, 7, 14, 28, and 56 were assessed for growth parameters, hematological indices, biochemical markers, immune parameters, and injury patterns. Results revealed significant treatment effects across all measured parameters. The 1:1 ratio (T1) demonstrated optimal performance with highest specific growth rates ( C. striata : 1.88 ± 0.05%/day; H. fossilis : 1.69 ± 0.06%/day), lowest feed conversion ratio (1.85 ± 0.08), and superior survival rates ( C. striata : 93.3 ± 1.9%; H. fossilis : 90.0 ± 2.2%). Unbalanced ratios exhibited time-dependent stress responses that intensified linearly throughout the experimental period, evidenced by elevated RBC and WBC counts, reduced hemoglobin concentrations, increased glucose levels, enhanced antioxidant enzyme activities, diminished immune function, and elevated injury rates. The C. striata -dominant treatment (T3) produced the most severe physiological alterations and predatory injury patterns in H. fossilis due to intensified territorial aggression, while the H. fossilis -dominant treatment (T2) generated the highest self-inflicted injuries in H. fossilis resulting from crowding-induced erratic swimming behavior. This study establishes that a 1:1 stocking ratio optimizes production performance and fish welfare in polyculture systems under the distinctive environmental conditions of hill climates, providing valuable insights for sustainable aquaculture development in similar regions globally.