Do different light regimes affect the foraging behaviour, growth and survival of larval cod (Gadus morhua L.)?

One of the problems encountered with intensive production of Atlantic cod (Gadus morhua L.) is inconsistent growth and survival from hatch through metamorphosis. This could be attributed in part to a poor understanding of the optimal culture conditions required for large-scale commercial production. Studies to date have indicated that cod larvae reared under high light intensities perform better than larvae reared under low light intensities. However, an earlier study from our laboratory suggested that Atlantic cod may not require high light during the later larval stages. Therefore, this study examined the foraging behavior, growth and survival of Atlantic cod larvae reared under varying light conditions during the late larval stage. In this experiment, larvae were subjected to three different light intensity regimes: treatment 1-2200 lux from 3-58 days post-hatch (dph), treatment 2-2200 lux from 3-27 dph and 600 lux from 28-58 dph and treatment 3-2200 lux from 3-39 dph and 600 lux from 40-58 dph. All tanks were kept under 24 h light. Weekly length and weight measurements were taken, and foraging behaviour was recorded twice a week. The results show that larvae reared in treatment 2 showed better growth in terms of standard lengths and dry weights than the larvae reared in treatments 1 and 3. Larvae reared in treatment 2 were also more efficient foragers than the other two treatments. However, there were no differences in the survival among the three treatments. These results indicate that a reduction in light intensity in cod larval tanks during the late larval stages would enhance the growth performances.