Prolonged photoperiod improves the growth performance for a hatchery reared right-eyed flatfish

Rearing winter flounder (Pseudopleuronectes americanus) in captivity for aquaculture and stock enhancement is a viable option to relieve fishing pressure and aid in ongoing recovery strategies. The objective of this study was to determine the effect of photoperiod on growth and survival of young-of-the-year juvenile winter flounder. Juveniles were reared for 12 weeks at three photoperiods: 24 light/0 dark, 18 light/6 dark, and 12 light/12 dark. Twenty fish were stocked into each of 18 enclosures with six enclosures per treatment. Fish in all treatments were fed to satiation every four hours. All fish were imaged at stocking and at three-week intervals. Growth was measured as changes in standard length (SL) and body area (BA). As early as Week 3, fish in all treatments were significantly different in terms of SL and BA. In general, fish grown under continuous 24 light were the largest and fish in the 12 light/12 dark regime were the smallest. Maximum specific growth rates of 0.41 % per day for SL and 0.83 % per day for BA were achieved in the 24 light/0 dark photoperiod. Average mortality rate over the course of the experiment was 9.17 % and there were no significant differences in the number of dead fish among the treatments. In conclusion, this study demonstrates that a longer day coupled with available food will increase growth rate for winter flounder juveniles, without affecting survival. By extending the photoperiod, growth in young-of-the year winter flounder is accelerated, bringing the growth rate of winter flounder close to that of other commercially produced flatfish.