RESUMO
In fish /<4 g, the parasite caused proliferation of the epithelial lining of the secondary gill lamelae resulting in fusion of the lamellae. Blood vessels feeding lamellae congested resulting in a degeneration of the lamellae epithelium. There was a high incident of mortality among small fish harboring the parasite. Large fish [>/10 g] were also adversely affected by T. piscium although morality was reduced. Branchial epithelial cells increased in size, blood vessels in the primary and secondary gill lamellae became dilated, and there was extensive hyperplasia in the epithelial lining of the primary gill filaments. Short term [30 minutes] treatments with formalin at three concentrations [300, 400 and 500 ppm] and copper sulfate at one concentration [20 ppm were unsuccessful in eradicating the parasites from the gills. However, treatment with 5 ppm of formalin over a 4 day period and 1, 2 and 5 ppm copper sulfate cleared the parasites from the fish completely within 24 hours period