Effect of photoperiod on growth and survival of snapper Pagrus auratus larvae

Abstract

Experiments were done in 100-l recirculation tanks to determine the effects of photoperiod on (1) first-feeding and (2) post-swimbladder inflated snapper, Pagrus auratus, larvae. In Experiment 1, feeding onset, growth, initial swimbladder inflation, and tail flexion were assessed at five photoperiod treatments (0L:24D, 6L:18D, 12L:12D, 18L:6D, and 24L:0D) in larvae from 3 to 15 days after hatching (dah). Growth and development of first-feeding larvae increased with increasing photoperiod duration in the 12L:12D to 24L:0D treatments. Larvae did not start feeding in 0L:24D and onset of feeding was delayed by up to 3 days in 6L:18D. All larvae held in 0L:24D and 6L:18D died within 6 or 9 dah, respectively. Initial swimbladder inflation was best (80–100%) in an intermediate photoperiod of 12L:12D at 9 dah. By 15 dah, although the percentage of larvae with inflated swimbladders had increased in all treatments, swimbladder inflation in 12L:12D was 1.3 and 2.0 times greater than that of larvae in 18L:6D and 24L:0D, respectively. In the second experiment, growth and survival of snapper after the initial swimbladder inflation period (11–32 dah) were assessed at three photoperiod treatments (12L:12D, 18L:6D, and 24L:0D). Growth was greatest in 18L:6D in which wet weights (16.3±0.5 mg; mean±S.E.) and dry weights (2.8±0.1 mg; mean±S.E.) of larvae were approximately 1.3 and 1.9 times heavier than the larvae held in 24L:0D and 12L:12D, respectively. Survival of snapper larvae to 32 dah was not significantly different between the three photoperiod treatments, but power of the experiment to detect effects on survival was small due to large variability within treatments. Further research is needed to determine optimal photoperiods for the survival of the snapper larvae. Because of the potential for large larval mortality, if initial swimbladder inflation is not achieved, the optimal photoperiod for the period from feeding onset to swimbladder inflation (3–15 dah) was deemed to be 12L:12D, whereas on the basis of growth parameters that were measured (total length, wet and dry weights), 18L:6D was determined to be the optimal photoperiod for the culture of snapper from the post-swimbladder window to metamorphosis (11–32 dah).