WASTE-WATER MANAGEMENT PLANT EFFLUENTS CAUSE CELLULAR ALTERATIONS IN THE SKIN OF BROWN TROUT

To assess the impact of a sewage plant on fish, brown trout Salmo trut ta were kept in two cages for 55 days in a moderately polluted river u pstream of a sewage plant. In one of the cages, undiluted treated wast e water of the sewage plant (WWE) was added at an average concentratio n of 5%, whereas the other cage received river water (R) only, A high mortality occurred in the WWE group. In comparison to control trout he ld in tap water, the skin structure and ultrastructure were altered cl early in both groups exposed to river water, including necrosis, apopt osis, decreased number of mucous cells, decrease in epidermal thicknes s, invasion of leucocytes, extension of melanocytes into the epidermis , being gradually more prominent in the WWE group. The most obvious di fference between the two exposed groups was found in structure, size a nd electron density of the secretory vesicles of the filament cells. T his and the observed vacuolation of Golgi saccules are indicative for disturbances in the secretory pathway of the filament cells. Certain t oxins were suspected to cause the decompaction of myelin sheaths demon strated in both groups. Reasons for the rather minor overall differenc es between the exposed groups are discussed, The extremely high mortal ity rate in the WWE group supports the importance of reducing the load of pollutants in the effluent of the waste-water management plant. (C ) 1997 The Fisheries Society of the British Isles.