Channel catfish response to ultraviolet-B radiation

Fingerling channel catfish Ictalurus punctatus exposed to simulated ultravi olet-B radiation at an average daily dose of 2.9 J/cm(2) were quite sensiti ve to the radiation. After a 24-h exposure, thinning of the most dorsal epi dermis frequently was accompanied by edema. Compared with epidermis of unex posed fish, mucous cells in exposed fish were less superficial and club cel ls were less numerous both dorsally and high on the lateral surface of the body. Sunburn cells with pyknotic nuclei were evident in the epidermis of e xposed fish. Among fish exposed for 48 h, focal necrosis and sloughing of t he outer epidermal layer were widespread. A methonol-extractable skin subst ance that is associated with resistance to sunburn in other fish species wa s not detected in channel catfish.