The effects of ultraviolet radiation on a freshwater prey fish: physiological stress response, club cell investment, and alarm cue production

Recent anthropogenic activities have caused deleterious effects to the stratospheric ozone layer, resulting in a global increase in the level of ultraviolet radiation (UVR). Understanding the way that organisms respond to such stressors is key to predicting the effects of anthropogenic activities on aquatic ecosystems and the species that inhabit them. The epidermal layer of the skin of fishes is not keratinized and acts as the primary interface between the fish and its environment. The skin of many species of fishes contains large epidermal club cells (ECCs) that are known to release chemicals (alarm cues) serving to warn other fishes of danger. However, the alarm role of the cells is likely secondary to their role in the immune system. Recent research suggests that ECCs in the epidermis may play a role in protecting the fish from damage caused by UVR. In the present study, we examined the effects of in vivo exposure to UVR on fathead minnows (Pimephales promelas), specifically investigating ECC investment, physiological stress responses, and alarm cue production. We found that fish exposed to UVR showed an increase in cortisol levels and a substantive decrease in ECC investment compared to non-exposed controls. Unexpectedly, our subsequent analysis of the behavioural response of fish to alarm cues revealed no difference in the potency of the cues prepared from the skin of UV-exposed or non-exposed minnows. Our results indicate that, although nonlethal, UVR exposure may lead to secondary mortality by altering the fish immune system, although this same exposure may have little influence on chemically-mediated predatorprey interactions. (c) 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 832841.