Effects of light intensity and photoperiod on survival and growth of walleye pollock (Gadus chalcogrammus) larvae

This study investigated the survival rates and growth of larval walleye pollock (Gadus chalcogrammus) reared at different photomanipulation. Larval walleye pollock were reared at four light intensities (experiment 1: 50, 250, 1000 and 2500 lux) and five photoperiods (experiment 2: 24L:0D, 18L:6D, 12L:12D, 6L:18D and 0L:24D) from hatching (30 days post hatch). Survival of larval fish of experiment 1 was >15% and there was no significant difference between 50, 250, and 1000 lux, however, whole fish was dead at 16 days post hatch in 2500 lux. Growth of larvae at 1000 lux was greater than larvae at all other light intensities treatments. Survival rates of experiment 2 was >14% except for 0L:24D, and 18L:6D was significantly higher than that of larval fish reared at other photoperiods. In 0L:24D, the death occurred continuously after initial of experiment, whole larval fish died on 21 days post hatch. Growth of larvae that illuminated the light more than 12 hours were higher than that of larvae reared at 6L:18D. Considering these results, the optimal rearing light intensity and photoperiod was 1000 lux and 18L:6D, respectively. Further, intensive light or lightless condition cause mortality of walleye pollock larvae.