Environmental impact assessment of stocking density in bamboo cage aquaculture: examining water quality dynamics, stress biomarkers, and ecosystem response in a subtropical forest water body of Northeast India

Forest-dependent communities in India, particularly in the Northeast region, face significant socio-economic challenges while possessing vast untapped aquatic resources. This study investigated the environmental sustainability of varying stocking densities (5–20 fish/m3) of Indian major carp Catla catla in eco-friendly bamboo cages within a forest water body in Tripura, Northeast India, intending to develop low-cost aquaculture solutions for forest dwellers. Water quality parameters, stress biomarkers, and ecosystem responses were monitored over 6 months. Results demonstrated optimal environmental and economic sustainability at 15 fish/m3, maintaining acceptable water quality (DO 5.6 ± 0.6 mg/L, ammonia-N 0.28 ± 0.04 mg/L) while maximizing production efficiency (survival 86.8 ± 2.1%, FCR 2.26 ± 0.14). Higher densities significantly increased environmental stress indicators, including elevated cortisol levels (26.5 ± 4.2 ng/mL) and reduced plankton diversity (Shannon–Wiener index 2.21 ± 0.15). Economic analysis revealed the highest profitability at 15 fish/m3 with a benefit–cost ratio of 1.83 ± 0.05 and net returns of Rs. 4311 ± 186 per cage, highlighting its commercial viability. The 15 fish/m3 treatment achieved optimal production (47.65 ± 1.86 kg/cage) while maintaining environmental parameters within acceptable limits. The study provides evidence-based guidelines for environmentally and economically sustainable cage aquaculture, offering viable livelihood opportunities for forest-dependent communities while preserving ecosystem integrity.