Abstract: The half-smooth tongue-sole （Cynoglossus semilaevis Gu ntuer） with body weight of （ 120.65± 1.57g）were reared in circu- lar 0.75 m： bottom surface area tanks at a rate of 30 fish/tank under photoperiod of 0L：24D, 6L： 18D, 18L：6D and 24L：0D for 28d at water temperature of 25.2 -8.2℃ to evaluate effects of photoperiod on growth and antioxidant index.. The results showed that the minimal food conversion ratio, and the maximal weight gain rate and net weight gain were observed in the fish in photoperiod of 6L/18D. Under the photoperiod of 24L/0D, the maximum specific activity of superoxide dismutase （SOD） was found in the liver of the fish while there were no significant differences in SOD activity in the spleen and kidney （P〉0.05）. The maximal specific activity of catalase （CAT） was found in the serum in photoperiod of 6L/18D, significant higher in spleen in 6 L/18D than that in other groups （P〈0.05）. There were no significant differences in CAT activity in liver and kidney under four photoperiods （P〉0.05）. There was sig- nificant higher glutathione （GSH） content in the liver than that in the serum, spleen and kidney （P〈0.05）. The GSH content in the liv- er was found significantly higher in 6L/18D than that in OL/24D and 24L/0D （P〈0.05）while the malonaldehyde （MDA）content in serum significantly lower than that in other groups （P〈0.05）. The MDA in the liver was found to be the minimum in 0L/24D, signifi- cant higher in 18L/6D than that in 0L/24D （P〈0.05）. The minimum MDA activity in spleen and kidney was observed in 6L/18D, indicating that 6L/18D is the optimum photoperiod for growth of the fish.

Key words: photoperiod, Cynoglossus semilaevis Guntuer, antioxidation, growth