EFFECTS OF ULTRAVIOLET-B RADIATION ON FISH - HISTOLOGIC COMPARISON OFA UVB-SENSITIVE AND A UVB-TOLERANT SPECIES

Lahontan cutthroat trout Oncorhynchus clarki henshawi were sensitive t o simulated solar ultraviolet-B radiation (UVB) and exhibited grossly visible signs of sunburn upon exposure. Razorback suckers Xyrauchen te xanus, however. were tolerant to simulated solar UVB and showed no gro ssly visible signs of exposure. Cutthroat trout also had considerably less of an unidentified, possibly photoprotective, substance in the sk in than did razorback suckers. In an attempt to characterize the cellu lar response to simulated solar UVR exposure in the skill of these two species. we examined sections from UVB-exposed fish by light and elec tron microscopy. Cutthroat trout showed grossly visible signs of sunbu rn by 48 h. Histologic observations included a sloughing of the mucous cells. necrosis and edema in the epidermis and dermis, and, in some c ases, secondary fungal infections. Razorback suckers did not show any visible signs of sunburn during 72 h of experimental exposure. Histolo gic analyses revealed that cell necrosis had occurred. but the severe necrosis and sloughing noted in cutthroat trout was not observed. An i ncrease in epidermal thickness, apparently due to hypertrophy and hype rplasia of large PAS-negative calls, occurred in the razorback suckers . These cells contained a large central region of low electron density and appeared to he club cells. In some, extensive interdigitation of the electron-lucent cytoplasm with adjacent epithelial cell margins oc curred. Near the surface of the epidermis these cells were larger and the interface with epithelial cells lacked complex interdigitation. Th ese cells may contain the substance that appears To protect razorback suckers against UV-B radiation.