UTTAR PRADESH JOURNAL OF ZOOLOGY

Water quality, especially pH levels, is crucial for the survival, growth, and health of fish in aquaculture environments. An experimental 30‑day study was conducted to evaluate the histopathological effects of extreme pH conditions on Labeo rohita fingerlings. Sub‑lethal pH treatments of 4.5, 5.0, 7.0, 9.5 and 10.0 were maintained in 500‑L FRP tanks filled with 300 L of water, with pH 7.0 serving as the neutral control. Water pH was adjusted using 0.5 N HCl or 1.0 N NaOH and monitored daily with a digital meter. Fifty fingerlings were stocked per tank and fed a commercial diet (30 % protein, 3 % fat) at 4 % body weight twice daily. Water quality was managed through 20 % weekly water exchange and constant aeration. After 30 days, fish were sampled from each treatment for histopathological analysis; survivors were then transferred to tap water for a 14‑day recovery period, with additional sampling at the end of recovery. Gill tissues from acidified and alkaline treatments exhibited epithelial lifting, telangiectasia, congestion, lamellar curling, aneurysms, necrosis, and vacuolation; liver tissues showed hepatocyte degeneration, necrosis, haemorrhage, blood congestion, and vacuolation. Lesions were most severe at pH 4.5 and 10.0. Fish at pH 5.0 and 9.5 showed partial restoration of tissue architecture during recovery, whereas those exposed to pH 4.5 or 10.0 displayed persistent damage. The findings underscore the importance of maintaining water pH within the optimal range of 6.5–9.0 to ensure normal physiological and metabolic functioning in Labeo rohita. Extreme pH deviations can severely damage gill and liver morphology, compromising fish health and survival. The study highlights the necessity for regular monitoring and management of pH in aquaculture ponds to prevent long-term stress and mortality. Future research should focus on molecular-level responses and the cumulative effects of pH in combination with other environmental stressors.