The effect of varying light intensities and tank colour on the growth, foraging behaviour and survival of Atlantic cod (Gadus morhua) larvae

Monk, Jennifer Grace Elizabeth (2008) The effect of varying light intensities and tank colour on the growth, foraging behaviour and survival of Atlantic cod (Gadus morhua) larvae. Masters thesis, Memorial University of Newfoundland.

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Abstract

One of the problems encountered with intensive production of Atlantic cod (Gadus morhua) 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 higher light intensities perform better than larvae reared under lower light intensities. The present study examined the growth, survival and foraging behaviour of Atlantic cod larvae reared under varying light conditions and tank colour. Weekly length and weight measurements were taken, and foraging behaviour was observed twice a week and the orientation frequency, number of capture attempts, number of capture misses as well as the length of time spent swimming versus the amount of time the larvae spent motionless were recorded. -- In the first experiment, cod larvae were reared in three different light intensity regimes: treatment 1 used 2200 lux from 3-58 days post hatch (dph), treatment 2 used 2200 lux from 3-27 dph and 600 lux from 28 - 58dph, treatment 3 used 2200 lux from 3-39 dph and 600 lux from 40 - 58 dph. The results demonstrated that larvae reared in treatment 2 had better growth at the end of the experiment in terms of standard lengths (17.7 mm) and dry weights (0.068 mg) than the larvae reared in treatments 1 (12.3 mm, 0.0338mg) and 3 (14.1 mm, 0.040 mg). Larvae reared in treatment 2 were also shown to be more efficient foragers than larvae from the other two treatments, based on the Modal Action Pattern (MAP) analysis. However, there were no significant differences in the survival between the three treatments. The results of this study indicated that beyond 27 dph it is not optimal to rear larvae under high light intensities and that the light intensity could be reduced at an earlier stage than previously thought. -- In the second experiment, larvae were reared in tanks with black walls and either light (beige) or dark (black) bottoms under the light regime from experiment one that provided the best growth. Results showed no significant differences in the growth, foraging behaviour or survival of Atlantic cod larvae in response to tank bottom colour indicating that larvae can be reared in lighter bottomed tanks without any detrimental effects to the behaviour, growth and survival of the larvae. This finding is beneficial to the culturists as light coloured tank bottoms provide the opportunity to monitor larval development and behaviour closely.

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