A preliminary study into the effectiveness of stroboscopic light as an aversive stimulus for fish

To reduce fish mortality in nature it is often necessary to expel individuals from areas modified by humans (e.g., dams) where they could be injured or killed. We tested the effectiveness of stroboscopic light as an aversive stimulus for zebrafish (Danio rerio) in captivity. We used six groups of five zebrafish with the groups subjected to three sequential experimental treatments, which each lasted 7 days. Treatment 1 (Control): the fish were maintained in an aquarium, which was divided physically into left and right sides. Treatment 2 (Enrichment): the left side of the aquarium was enriched with a variety of objects. Treatment 3 (Stroboscopic light): a stroboscopic light was aimed at the enriched side (left) of the aquarium. In each treatment, fish were acclimatized for 3 days and then filmed for 90 min on four consecutive days. Using scan sampling with instantaneous recording of behaviour (30 s interval) we recorded the number of fish visits to each side of the aquarium. Fish did not show any side preference in Treatment 1 (P > 0.05), during Treatment 2 they preferred the enriched (left) side of the aquarium (P < 0.05) and in Treatment 3 they again showed no side preference (P > 0.05). A Friedman's test confirmed that avoidance of the stroboscopic light lasted until almost 22.5 min. These results suggest that stroboscopic light can be temporarily effective in removing fish from a preferred area.