Foraging, growth and survival of Atlantic cod larvae reared in different light intensities and photoperiods

Studies have shown that most marine fish larvae are visual feeders and their, feeding incidence increases with light intensity. Although laboratory studies on photoperiod showed variable results, evidence from the field suggest that larvae exposed to a continuous light may grow better than larvae exposed to reduced photoperiods. We set up experiments to investigate the foraging, growth and survival of Atlantic cod larvae (Gadus morhua; Grand Banks origin) at different light intensities and photoperiods. Behavioural observations were also carried out in an attempt to explain any differences in the performance of cod larvae under varying light intensities. Larval cod were reared at four light intensities (300, 600, 1200 and 2400 lx or 4.93, 10.96, 19.89 and 37.32 muE m(-2), respectively) and three photoperiods (24 L:0 D, 18 L:06 D and 12 L:12 D) from hatching to metamorphosis (42 days post-hatch; dph). Cod larvae grew and survived better in higher light intensity (2400 lx) and 24 L:0 D photoperiod. Examination of the foraging indicated that cod larvae reared in higher light intensity captured prey more efficiently than larvae reared in low light. Results also showed that the mortality rates of larval cod from 2400 lx and 24 h photoperiod were significantly lower than the larvae from other light intensity and photoperiod treatments until 28 dph. This indicates that photoperiod and light levels could be reduced beyond 28 dph. (C) 2002 Elsevier Science B.V. All rights reserved.