ULTRAVIOLET PHOTORECEPTION CONTRIBUTES TO PREY SEARCH BEHAVIOUR IN TWO SPECIES OF ZOOPLANKTIVOROUS FISHES

We tested the hypothesis that ultraviolet photoreception contributes to prey search in small juvenile rainbow trout (Oncorhynchus mykiss) and pumpkinseed sunfish (Lepomis gibbosus) while foraging on Daphnia pulex. Small individuals of these species are ultraviolet-photosensitive zooplanktivores. For both species, prey pursuit distances and angles were larger under full-spectrum illumination than under ultraviolet-absent illumination. The same was true for the distances and angles associated with repositioning movements (i.e. those not leading to the location of a prey item). Thus, ultraviolet photoreception contributes to prey search and detection in these fishes. We argue that the most likely mechanism underlying this enhancement of prey search abilities is improved target contrast.