The physiological ecology of UV-absorbing compounds from the mucus of marine fishes

Abstract

This dissertation details my investigation into the physiological ecology of UV-absorbing compounds found in the mucus of marine fishes. In a survey of over 200 species of fishes from around the Pacific, I found that approximately 90% of fishes possess mucus that absorbs strongly in the UV. High-performance liquid chromatography of selected mucus confirmed that the UV-absorbing compounds in the mucus are mycosporine-like amino acids, or MAAs. I determined that the mucus of experimentally UV-exposed Thalassoma duperrey absorbs more strongly in the UV than the mucus of those protected from UV by UV-opaque (but visible light transparent) plastic. However, this difference in mucus absorbance only occurs if fish are provided a dietary source of MAAs. Furthermore, I found that males have higher mucus absorbance than females, and females exposed to UV suffer high rates of skin damage. Females also sequester MAAs in their eggs, and may suffer a conflict of interest between providing sunscreen protection for their eggs vs. their own skin. Three coral reef fish species (Canthigaster jactator, Chaetodon multicinctus, and Thalassoma duperrey) were sampled over a depth gradient, and shallow water fish generally had superior sunscreen, both in terms of magnitude and - spectral shifting, as compared with deeper water individuals of the same species. Temperate tidepool sculpins (Family: Cottidae) showed a significant loss of UV-absorbing compounds with increasing north latitude, and overall, fishes from higher tidepools had more sunscreen than fishes from low tidepools. Behavioral experiments with Thalassoma duperrey showed no dietary or UVinduced differences in weight loss or swimming behavior, and the results on shadeseeking behavior were equivocal. Thus, sunscreening compounds seem to be ubiquitous among marine fishes. The correlations I have found between the UV absorbance of mucus and the depth, latitude, or UV exposure of the sampled individual lead me to believe that mucus UV absorbance is an adaptive defense against UV for fishes.