Effect of thermal stress on dietary requirement of vitamin C in thornfish Terapon jarbua

Attempts are made to elucidate the optimal dietary requirement of vitamin C in thornfish Terapon jarbua cultured at 28, 32 and 36 degrees C, separately. The fish were fed diets with 0, 80, 400 and 2000 mg/kg vitamin C-supplement for 8 weeks. The growth was the best when the fish fed diet with 400 mg/kg vitamin C-supplement and cultured at 36 degrees C. The mortality of fish increased with increasing water temperature, but decreased with increasing the amount of vitamin C supplemented in diets. The deformed fish appeared at 36 degrees C when fish were fed diet supplemented no more than 80 mg/kg vitamin C. The vitamin C level and hydroxyproline/proline ratio in the fish tissues increased with increasing the amount of vitamin C supplemented in diets. Both variations of vitamin C level and hydroxyproline/proline ratio in thornfish were similar to each other. Judging from the data of growth, feed conversion factor, vitamin C level and hydroxyproline/proline ratio, the optimal level of vitamin C in the diet for thornfish was 80 mg/kg when fish were cultured at 28 and 32 degrees C, but it had to be elevated to 400 mg/kg when fish were cultured at 36 degrees C.