Abstract
Purpose: :
While the zebrafish retina is known to possess ultraviolet (UV) sensitive photoreceptors, the functional significance of UV sensitivity in zebrafish is unknown. Because UV light can be potentially harmful to developing fish, especially at early stages when they are transparent, we tested the effects of UV light on their behavior and survival.
Methods: :
A forced-preference, phototaxis assay was used to measure the behavioral response of wild type and retinal mutant fish lots-of-rods (from ages 3-43 days post fertilization (dpf)) to UV (300-400 nm) and visible light (400-700 nm). Using UV emitting lights with UV blocking filters, we measured phototaxis behavior in test containers that were half irradiated by UV or visible light. We scored the number of fish present under the container half with either no UV or visible light after 10 minute light exposures. We also measured the effects of UV light exposure on the survival of larval fish. We exposed fish (3-10 dpf) to three lighting regimes: either UV, no UV, or half UV for 10 days (14 hours day: 10 hours night light cycle).
Results: :
3 dpf fish did not respond at all to UV or visible light. Between 4-16 dpf zebrafish exhibited robust phototaxis to visible light. However, from 4 dpf and on, fish robustly exhibited UV avoidance behavior, maximally between 4-10 dpf. The mutant fish lots-of-rods, which do not have UV photoreceptors, did not exhibit UV avoidance behavior at any age. Furthermore, fish exposed to UV light exhibited greater mortality compared to fish exposed to no UV and half UV.
Conclusions: :
UV sensitivity is functional in zebrafish as early as 4 dpf. While larval zebrafish exhibit positive phototaxis to visible light, they exhibit a clear avoidance behavior to UV light. Exposure to UV appears harmful to larval zebrafish in that those exposed to UV light suffer greater mortality than those not exposed.
Keywords: visual development