Effect of photoperiod manipulation on the growth performance and stress response of juvenile red sea bream ( Pagrus major)

Juvenile of red sea bream ( Pagrus major, body weight 1∼30 g) were reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) with constant light intensity 1500 lx on the water surface to investigate their growth performance and stress response. Fish were fed a commercial diet to apparent satiation for 8 weeks of the experiment. Significantly higher weight gain and specific growth rates (SGR) were observed in fish exposed to a 24L:0D photoperiod followed by 16L:8D, 6L:6D and 12L:12D photoperiods ( P < 0.05). Food intake was significantly higher in fish exposed to 24L:0D followed by 6L:6D, 16L:8D and 12L:12D photoperiods ( P < 0.05). There was no significant difference in the feed conversion efficiency (FCE) between fish exposed to 24L:0D and 16L:8D photoperiods, but the FCE in both photoperiods was significantly higher than that of 6L:6D and 12L:12D photoperiods. There were no significant differences in hematocrit levels and plasma levels of cortisol and glucose among the treatments at the end of experiment. The results demonstrated that the growth performance of juvenile red sea bream reared from 1 to 30 g can be stimulated significantly by using a continuous (24L:0D) photoperiod without any measurable significant stress response in fish.