Effects of ultraviolet radiation on the eggs of landlocked Galaxias maculatus (Galaxiidae, Pisces) in northwestern Patagonia

1. Ultraviolet radiation (UVR) damages early life stages of several fish species. Galaxias maculatus is a small catadromous fish, with landlocked forms occurring in many lakes within the Nahuel Huapi National Park (Patagonia, Argentina). Tn this work, the vulnerability of G. maculatus eggs exposed to both natural and artificial UVR was investigated in relation to water transparency. 2. Field experiments were performed in two lakes differing in UVR attenuation. Galaxias maculatus eggs were exposed to in situ levels of UVR in quartz tubes incubated at various depths. For laboratory experiments, the eggs were exposed to five levels of artificial UVB radiation. 3. Exposure to natural UVR causes various degrees of egg mortality depending on water transparency and incubation depth. In the less transparent lake (K-d320 = 3.08 m(-1)), almost complete mortality was observed near the surface. At a depth of 43 cm the observed mortality was only 22%, but was still significantly different from the dark control. In the most transparent lake (K-d320 = 0.438 m(-1)), almost total mortality was observed in tubes incubated at 2.56 m or shallower. A gradual decline in mortality was recorded from that depth to 3.78 m where the values approached those in the dark control treatments. 4. A monotonic relationship between mortality and UV exposure could be observed both in field and laboratory experiments. Using the results from field incubations, a LD50 Of 2.5 J cm(-2) nm(-1) was estimated. In a few mountain lakes, this value would be exceeded even if the eggs were laid at the maximum depth of the lake. Thus UVR seems a sufficient cause to explain the absence of G. maculatus populations in some mountain lakes. For most lakes, however, UVR is probably one of several important environmental factors, which together determine the habitat suitability.