Vertical Avoidance of Ultraviolet-B Radiation in Japanese Flounder (Paralichthys olivaceus) Larvae

The amount of UV-B radiation has increased due to depletion of the ozone layer. It is well documented that exposure to UV-B increases mortality in marine fish larvae. However, UV avoidance behavior of fish larvae has received little attention. Here we test the hypothesis that Japanese flounder larvae stay deeper in the water column to avoid UV-B radiation. A UV-B lamp was placed above a tank. A larva was released near the surface of the tank. The vertical position of the larva was observed by eye every 15 seconds for 15 minutes that consists of 5 minutes × 3 phases, pre UV exposure, UV exposure and post UV exposure. Control treatment without UV-B radiation was also set. Trials were replicated 8 times for each treatment. In pre UV exposure, larvae stayed shallower than 10 cm in both UV-B and control treatment and no significant difference was observed. In UV exposure and post UV exposure, the average depth of larvae in UV-B treatment was significantly more than that of control treatment. Present results indicate that Japanese flounder larvae actively avoid UV-B radiation. We suggest that UV avoidance behavior should be taken into account to access UV-induced mortality in marine fish larvae.