Effects of light on the development, activity and mortality of halibut (Hippoglossus hippoglossus L.) yolk sac larvae
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Halibut yolk sac larvae were kept at different light intensities from Day 1 posthatch. Measurements of activity and swimming speed showed that larvae that were kept in darkness were more active, but had lower swimming speed than those kept in light. Larvae kept at 1000 lux had lower yolk sac utilization than larvae kept at lower light intensities, probably due to stress caused by light. Larvae kept at 1 and 10 lux had higher body dry weight when the experiment was terminated. Differences in pigmentation were found. An autecological model is discussed, suggesting that halibut yolk sac larvae are distributed in relatively shallow waters during the first week posthatch, thereafter sink into deeper waters, and rise again when the time of first feeding approaches.