THE EFFECTS OF TREATED DOMESTIC SEWAGE ON 3 ORGANS (GILLS, KIDNEY, LIVER) OF BROWN TROUT (SALMO-TRUTTA)

In an experiment extending over approx. 3 months, brown trout (Salmo trutta) were exposed to dilutions of biologically-treated wastewater (13, 24 and 42%) from a large sewage plant. The two higher concentrations caused a sequence of histological changes in the kidney and, after some delay, in the liver as well. No effects were detectable in the gills however. In all dilutions of the biologically-treated sewage, external injury of the fish was rapidly followed by fungal infection. Furthermore, kidney changes similar to those seen in the experiment were also observed in brown trout and rainbow trout (Oncorhynchus mykiss) caught downstream of the point at which the treated effluents from the sewage plant entered the River Inn. The pathogenic effects of ammonia and nitrite in the treated sewage are discussed.