The current study was conducted to evaluate the effects of UV-B radiation on survival rate and histopathological changes in the skin structure and ultrastructure in rainbow trout (Oncorhynchus mykiss) alevins. In laboratory dark conditions, newly hatched rainbow trout alevins were exposed to two different doses of UV-B radiation (high dose: HD: 94.83 μW cm(-2)) and (low dose: LD: 68.75 μW cm(-2)) for 9 days (time of exposure: 15 min per day), whereas specimens kept in darkness served as a control group. At the end of the experiment, alevins exposed to HD-UVB had the lowest survival rate (43.9 ± 0.9%), whereas fish exposed to LD-UVB showed intermediate values (73.6 ± 0.4%) with regard to the control group (91.2 ± 0.2%). Light microscopic and scanning electron microscopic studies revealed necrosis, sunburned cells, epidermis lifting of the epidermis, reduced number of mucous cells, degeneration of mucous cells and destruction of pavement cell microridges in both UV-B exposed groups. Hemorrhage and inflation in the meningeal layer of the brain were also observed in 17% and 42% of fish exposed to LD- and HD-UVB, respectively.
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