Physiological responses of Chinese longsnout catfish to water temperature

We evaluated the effect of water temperature on the growth and physiology of the Chinese longsnout catfish （Leiocassis longirostris Günther）. The fish were reared at four temperatures （20, 25, 30, and 35℃） and sampled on days 7, 20, and 30. We measured plasma levels of insulin, free thyroxine （FT4）, free 3,5,3＇-triiodothyronine （FT3）, lysozyme and leukocyte phagocytic activity. The optimum water temperature for growth was 27.7℃. The plasma levels of insulin and FT4 declined significantly （P〈0.05） on day 30 at temperatures above 20℃. Lysozyme activity was significantly （P〈0.05） lower at 25℃ than at other temperatures. We conclude that final weight, insulin, FT4, and lysozyme were significantly affected by water temperature.