Ultraviolet B Irradiation Affects Resistance of Rainbow Trout (Oncorhynchus mykiss) Against Bacterium Yersinia ruckeri and Trematode Diplostomum spathaceum

Abstract

Ultraviolet B (UVB) radiation is known to have various effects on the immune system of fish, but the effect on the actual disease resistance has remained largely unknown. Here we studied the effect of UVB on the resistance of rainbow trout (Oncorhynchus mykiss) against a bacterium Yersinia ruckeri, the causative agent of enteric red mouth disease, and a trematode parasite Diplostomum spathaceum, which causes cataracts in fish. The fish were exposed to UVB irradiation seven times in 14 days, and inoculated intraperitoneally with Y. ruckeri on day 5 after the first irradiation. On day 2 postinfection (p.i.), the number of viable bacteria in the kidney was lower in UVB-exposed than in unexposed fish. However, on day 8 p.i., UVB-irradiated fish had not been able to clear remaining Y. ruckeri effectively, and had a slightly higher bacterial load than controls. A similar, although not significant, effect was seen in the bacterial numbers in spleen. In the other experiment, fish were exposed to UVB for six consecutive days and then exposed to D. spathaceum. A significantly higher number of parasites was detected in the eyes of irradiated fish, indicating reduced resistance against the pathogen. Furthermore, UVB-irradiation altered the immunological and hematological parameters of fish, which also verified the immunomodulatory potential of UVB in the present study.

Larval UV exposure impairs adult immune function through a trade‐off with larval investment in cuticular melanin

“…; Markkula et al . ), our study is the first to show this effect in an invertebrate. Indeed, UV‐exposed larvae showed a reduction in a key measure of immune responsiveness in insects: a reduced melanotic encapsulation rate (Gillespie, Kanost & Trenczek ).…”

“…; Markkula et al . ). This seems especially relevant as melanin is a key molecule for invertebrate immunity (Siva‐Jothy, Moret & Rolff ).…”

Additive effects of enhanced ambient ultraviolet B radiation and increased temperature on immune function, growth and physiological condition of juvenile (parr) Atlantic Salmon, Salmo salar

“…Based on this, the results from the UVB-depleted group in the present study can be considered as a reasonable indicator of the effect on fish exposed to natural sunlight. UVB radiation negatively affects the immune system of fishes, and can affect disease resistance directly [47], or indirectly by inducing skin lesions and by exacerbating secondary bacterial and fungal infections [72,73]. Exposure to UVB radiation causes physiological stress manifested in changes in blood cortisol levels [21].…”

Effect of UV-B radiation on the antibody response of fish – Implication on high altitude fish culture

“…The mechanisms underlying this phenomenon should be investigated further in fish, for clearly identifying the mechanism of UV-B mediated immunosuppression. Fish death in experimental tanks is also compatible with the fact that UV-B radiation can cause immunosuppression in animals and making them susceptible to a variety of opportunistic infectious agents like bacteria and viruses [37,38].…”