Ultraviolet B Radiation Induced Alterations in Immune Function of Fish In Relation to Habitat Preference and Disease Resistance

Markkula, Eveliina Ultraviolet B radiation induced alterations in immune function of fish, in relation to habitat preference and disease resistance Jyväskylä: University of Jyväskylä, 2009, 50 p. (Jyväskylä Studies in Biological and Environmental Science ISSN 1456-9701; 204) ISBN 978-951-39-3677-8 (PDF), 978-951-39-3651-8 (nid.) Yhteenveto: Ultravioletti B -säteilyn vaikutus kalan taudinvastustuskykyyn ja immunologisen puolustusjärjestelmän toimintaan Diss. Solar ultraviolet B (UVB) radiation is an environmental stressor known to have harmful impacts on aquatic organisms. While the immunomodulatory effects of UVB on fish have been demonstrated in short-term exposures, the present work focused on the long-term effects of low-dose UVB on fish species adapted to live at high or low levels of natural solar radiation. In general, the immunomodulatory effects of the long-term exposures with low UVB doses were less profound than those induced by short-term exposures. Suppressed functioning of head kidney phagocytes was detected after different exposure regimes ranging from a single UVB dose to an irradiation of 6 weeks, and was the most sensitive of the studied cellular parameters. Natural cytotoxic cells and lymphocytes were more inconsistently affected by radiation treatments, as were the hematological and humoral parameters of the blood. Cortisol-mediated stress reaction was common after short-term exposures. A comparison of the fish species revealed that benthic carp (Cyprinus carpio) is more sensitive to UVB than rainbow trout (Oncorhynchus mykiss), a representative species of clear water habitats. In outdoor experiments, the exposure simulating 20 % stratospheric ozone loss for 8 weeks negatively affected the growth, condition, and plasma IgM concentration of the juvenile Atlantic salmon (Salmo salar) indicating potentially compromised immune defense. The exposure simulating 8 % ozone loss for 20 weeks, however, caused no detectable change in fish when compared to the natural solar radiation. The relationship between the UVB exposure and disease resistance was demonstrated in rainbow trout irradiated over 1-2 weeks. Resistance of exposed fish to parasite Diplostomum spathaeum was significantly decreased, and clearance of bacteria Yersinia ruckeri from the tissues of infected fish was affected as well. The results suggest that increased UVB radiation levels can potentially harm fish health in long-term exposures, and that there is an association between UVB exposure and disease resistance.