Fluence rate or cumulative dose? : Vulnerability of larval northern pike (Esox lucius) to ultraviolet radiation

Newly hatched larvae of northern pike were exposed in the laboratory to four fluence rates of ultraviolet radiation (UVR; 290–400 nm) over three different time periods, resulting in total doses ranging from 3.0 ± 0.2 to 63.0 ± 4.4 kJ·m−2. Mortality and behavior of the larvae were followed for 8–12 days, and growth measured at the end of the experiment. Also, the principle of reciprocity—that the UVR-induced mortality depends on the cumulative dose, independent of fluence rate—was tested. Fluence rates higher than 1480 ± 150 mW·m−2 caused mortality and growth retardation. The highest fluence rate (3040 ± 210 mW·m−2) caused 100% mortality in 5 days. All fluence rates caused behavioral disorders, which led to death at fluence rates higher than 1480 mW·m−2. Reciprocity failure occurred with the lowest and highest dose (550 ± 45 and 3040 ± 210 mW·m−2, respectively). The results show that fluence rate is of primary importance when assessing the UVR-related risk.