Influence of solar ultraviolet-B on pelagic fish embryos: osmolality, mortality and viable hatch

Eggs of dab (Limanda limanda) and plaice (Pleuronectes platessa) were exper imentally exposed to ultraviolet-B (UV-B) radiation in a solar radiation si mulator. The experimental design tried to simulate present and future condi tions with reference to increased UV-B exposure due to northern hemisphere ozone loss, employing mainly two scenarios, a reduction to 270 (S1) and to 180 (S2) Dobson units (DU) in single or repetitive exposures of 2, 4 or 6 h . Depending on the total dose of UV-B irradiation and the developmental sta ge, exposed eggs displayed loss of buoyancy as a sublethal effect, as well as increased embryo mortality and reduced viable hatch. In the single expos ure experiments only under conditions of 180 DU for 6 h were effects appare nt. Double exposure under conditions of 270 DU did not lead to lasting effe cts. At the sublethal effect level, i.e. loss of buoyancy, considerable pho torepair was observed. It was concluded, that under the present general wea ther conditions in spring and at the present levels of environmental ozone, allowing for a reduction to 180 DU, the embryonic development of North Sea spring spawning fish is not endangered by UV-B radiation.