Female ovoposition behavior has important consequences on the survival of offspring because it determines both the biotic and abiotic environment in which eggs develop. While much consideration has been given to choices made in respect to predators, less is known about the consequences of ovoposition behavior with respect to vertical gradients in water columns. Female bluefin killifish (Lucania goodei) occur in the top 1-2 m of the water column and deposit eggs on floating and benthic vegetation. Ultraviolet (UV) wavelengths are most abundant near the surface and decrease as depth increases. The goal of this project was to determine the extent to which bluefin killifish selectively lay their eggs near the surface of clear and tea-stained water and to further examine possible ultimate causes behind this behavior, with a focus on the effects of UV light.
Killifish were raised in 2 light environments (clear and tea stained water) and given the choice of spawning in shallow or deep substrate. The number of eggs laid in each was then compared. In addition we examined the incubation period and egg survival under full spectrum, UV deficient, and diminished lighting (as a control for decreased light under UV deficient treatment).
Results/Conclusions
Bluefin killifish (Lucania goodei) preferentially lay their eggs near the surface of the water in both clear and tea stained water (p<0.05). The proportion of eggs laid at the surface by animals raised and tested in tea stained water tended to be higher than the proportion of eggs laid at the surface by animals raised and tested in clear water (p=0.07). UV light is filtered out faster in tea stained water. Eggs ovoposited at the surface are exposed to more UV which reduces egg survival. Why females do this is unclear. One possible explanation is that laying eggs high in the water column decreases cannibalization rates from adult fish. Another explanation could be that females use the UV light to defend against parasites.
UV light has been shown to increase the toxicity of Polycyclic aromatic hydrocarbons (PAHs) which have been suggested to be the most common water pollutants from antibiotics. Increasing levels of antibiotics in wastewater combined with increasing UV light intensity due to global warming could effect the development of eggs in species which preferentially oviposit near the surface where UV light is the most intense and raises the possibility of previously unexamined consequences from pollution to aquatic ecosystems.
