Effects of acclimation temperature on growth, physiology and thermal tolerance of the juvenile grass carp Ctenopharyngodon idella

Aquatic ichthyofauna are facing unfavourable temperature fluctuations due to the anthropogenic activities and global climate change. Effects of temperature in aquatic environments need to be explored for revealing its potential effects on the aquatic organisms. In present study, the effects of different acclimation temperatures on the oxidative stress, metabolism, thermal tolerance and growth of the grass carp Ctenopharyngodon idella were studied. Grass carp fingerlings (10.40 +/- 0.37 g) were reared for 60 days under different acclimation tempera -tures, i.e., 22 degrees C, 26 degrees C, 30 degrees C, 34 degrees C and 38 degrees C respectively. Significantly higher growth rate (weight gain and specific growth rate) and improved FCR of fish reared at 30 degrees C were observed, while under higher or lower acclimation temperatures, fish showed slow growth rate and high FCR. Growth rate in term of % weight gain and specific growth rate showed positive correlation with pyruvate kinase activity. Moreover, antioxidant parameters catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), lipid peroxidation (LPO), glutathione contents (GSH), glutathione peroxidase (GSH-Px), glutathione reductase (GR) in different tissues (liver, brain, gills, muscles and intestine) of fish showed decreasing trend from 22 degrees C towards 30 degrees C acclimation temperatures. However, beyond 30 degrees C, i.e., from 34 degrees C to 38 degrees C fish showed oxidative stress response, indicated by increasing trend in antioxidant parameter levels. Moreover, thermal tolerance data revealed that fingerlings of C. idella reared at highest acclimation temperature (38 degrees C) showed highest CTMax and CTMin values, while those reared at lowest acclimation temperature (22 degrees C) showed lowest CTMax and CTMin values. Our present study provides new insights regarding the thermal tolerance of fish and can be practically implemented in aquaculture sector.