Thermal stress response of different age group of Nile tilapia Oreochromis niloticus (Linnaeus, 1758) exposed to various temperature regimes

Climate change and temperature variations are of paramount importance to aquaculture. Here, we investigated the thermal stress response of five life stages of tilapia viz. spawn, fry, fingerling, juveniles and adults exposed to different temperatures (28°C to 40°C). Stress response was assessed in terms of survival/mortality, thermal shock, changes in hematology, histopathology of liver and gonad. The spawn, fry and fingerlings died within 1 to 39 min at 40°C due to thermal shock. Thermal acclimation was observed in these stages till 34°C. Beyond 34°C, low feed intake and susceptibility were marked. Significant increments in the hematological parameters were noticed when the water temperature elevated from 28°C to 32°C and thereafter deteriorated. Hematological parameters, gonadosomatic index (GSI), digestive somatic index (DSI) and hepatosomatic index (HSI) showed ideal conditions at temperatures between 28°C to 30°C. However, a marked change in the liver and gonad histoarchitecture and decreased organ somatic indices of adult tilapia were also noticed in response to elevated temperatures. This study suggests that the developmental stages of tilapia are highly susceptible to thermal shock and a gradual temperature rise helped them acclimate to 34°C. Further temperature rise may adversely affect tilapia aquaculture.