Effects of ultraviolet-b radiation on fish: Histologic comparison of a uvb-sensitive and a uvb-tolerant species

Ahontan cutthroat trout Oncorhynchus clarki henshawi were sensitive to simulated solar ultraviolel-B radiation (UVB) and exhibited grossly visible signs of sunburn upon exposure. Ra/orback suckers Xyrauchen texanus. however, were tolerant to simulated solar DVB and showed no grossly visible signs of exposure. Cutthroat trout also had considerably less of an unidentified, possibly photoprotective, substance in the skin than did razorback suckers. In an attempt to characterize the cellular response to simulated solar UVB exposure in the skin of these two species, we examined sections from UVB-exposed lish by light and electron microscopy. Cutthroat trout showed grossly visible signs of sunburn hy 48 h. Histologic observations included a sloughing of the mucous cells, necrosis and edema in the epidermis and dermis, and. in some cases, secondary fungal infections. Ra/orback suckers did not show any visible signs of sunburn during 72 h of experimental exposure. Histologic analyses revealed that cell necrosis had occurred, but the severe necrosis and sloughing noted in cutthroat trout was not observed. An increase in epidermal thickness. apparently due to hypertrophy and hyperplasia of large PAS-negative cells, occurred in the ra/orback suckers. These cells contained a large central region of low electron density and appeared to be club cells. In some, extensive interdigitation of the electron-lucent cytoplasm with adjacent epithelial cell margins occurred. Near the surface of ihe epidermis these cells were larger and the interface with epithelial cells lacked complex interdigitation. These cells may contain the substance that appears to protect razorback suckers against UV-B radiation.