High sensitivity of northern pike larvae to UV-B but no UV-photoinduced toxicity of retene.

In order to investigate whether increased UV-B radiation is a risk factor, a series of acute laboratory experiments was conducted with larval stages of the northern pike (Esox lucius L.), hatching in Nordic waters in May. Further, a comparative investigation on the acute phototoxicity of retene (7-isopropyl-1-methylphenanthrene), a PAH compound recently revealed to posses UV-B-induced phototoxicity in larval coregonids, was conducted with pike larvae. In semi-static experiment, larvae were pre-exposed to retene (3, 9, 30 and 82 microg/g), with relevant controls, for 24 h and then irradiated for 3 h once a day (two consecutive days) with three UV-B doses (CIE-weighted 1.0, 1.8 or 2.7 kJ/m2 per day) or with visible light only. In 3 days, the UV-B exposure alone increased mortality by 10-20% in all applied dose rates. Retene (up to 82 microg/l) had no direct UV-B-induced toxicity in pike. However, pike larvae were very sensitive to UV-B even in low doses, indicated as severe neurobehavioral disorders. Monitoring of pike with the neurobehavioral syndrome revealed substantial late mortality. As UV-B had no influence on CYP1A content in larval pike, retene (9-82 microg/l) induced this protein substantially with and without UV-B. In pike, the applied UV-B radiation and water retene alone both decreased HSP70 concentrations. Neither UV nor retene changed SOD activity significantly. Overall, data on pike suggest that only a minor increase in ambient UV-B coming to the earth's surface may cause lethal effects to larval fish.