Effect of solar ultraviolet radiation (280-400 nm) on the eggs and larvae of Atlantic cod (Gadus morhua)

In the Gulf of St. Lawrence, Canada, solar ultraviolet B radiation (UV-B, 280-320 nm) penetrates a significant percentage of the summer mixed-layer water column: organisms residing in this layer, such as the eggs of Atlantic cod (Gadus morhua), are exposed to W-B. In outdoor exposure experiments, Atlantic cod eggs were incubated in the presence versus the absence of UV-B and (or) UV-A (320-400 nm). We tested two hypotheses: H-1, UV-B induces mortality in Atlantic cod eggs, and H-2 W-A either exacerbates or mitigates any such W-B-induced mortality. Hypothesis H-1 was supported: there was a significant mortality effect on Atlantic cod eggs exposed to UV-B at the surface and at a depth of 50 cm. Hypothesis H-2 was not supported: there was no effect of UV-A. These experiments indicate that Atlantic cod eggs present in the first metre of the water column (likely only a small percentage of the total egg population) are susceptible to W-E. However, UV-B must be viewed as only one among many environmental factors that produce the very high levels of mortality typically observed in the planktonic early life stages of marine fishes.