Determination of optimal temperature(s) in juvenile red-spotted grouper Epinephelus akaara (Temminck & Schlegel) based on growth performance and stress responses

This study sought to determine the optimal temperature(s) for aquaculture of juvenile red-spotted grouper Epinephelus akaara (Temminck & Schlegel) (mean initial BW: 3.1g). Growth performance, insulin-like growth factor 1 (IGF-1) expression and thermal stress responses (plasma cortisol, glucose, and hepatic heat shock protein 60 expression) were evaluated at three constant temperatures (24 degrees C, 26 degrees C and 28 degrees C) in a 2-week trial. At the end of the trial, final BW was significantly higher at 26 degrees C and 28 degrees C than at 24 degrees C (p<0.05); a quadratic regression analysis of final BW showed the optimum temperature for growth was 27.5 degrees C (p<0.05, R-2=0.806). The highest hepatic IGF-1 expression was observed at 26 degrees C (p<0.05). On the other hand, hepatic heat shock protein 60 expression was highest at 28 degrees C (p<0.05), suggesting thermal stress. In conclusion, temperature optima, which support excellent growth but induce minimal thermal stress, was 26 degrees C. This fine information within a narrow temperature range is expected to give empirical information for red-spotted grouper farmers to sustain maximal production efficiency with avoiding thermal stress and to determine the future location of production, especially in consideration of arising seawater temperatures.