Effect of light intensity on the foraging and growth of Atlantic cod larvae:interpopulation difference?

Abstract

Studies have been conducted on the geographic variation of growth and survival among fish populations but little work has been done in this regard on the early larval stages of marine fish. We conducted experiments on larvae from 2 separate populations of Atlantic cod to determine their response to light. Preliminary experiments conducted in our laboratory suggested that the light intensity under which larvae were reared may affect the growth performance of Atlantic cod larvae from the Scotian Shelf (SS) and Northeast Grand Banks (NF) differently. We conducted experiments to test the hypothesis that light intensity differentially affects larvae from these 2 geographically distinct populations. Cod larvae from each population were reared under low (0.19 μE m-2 or 8.5 lx) and high (12.92 μE m-2 or 680 lx) light intensities. Results showed that NF larvae foraged, grew and survived better under high light than low light, while the SS larvae performed better under low light conditions. In nature, the population of SS cod we used spawn during late fall/early winter while NF cod spawn in spring/ summer. Thus, SS larvae likely experience low winter light levels and NF larvae high summer light levels during first feeding. These results support our hypothesis and suggest that cod larvae from different latitudes are adapted to local environmental conditions.