Comparative evaluation of the susceptibility of cultivated fishes to the natural infection with myxosporean parasites and tissue changes in the host

The purpose of the study was to evaluate the susceptibility of 4 important cultivated fishes to sporozoan parasites. Fishes were collected bimonthly from a pond for a period of 1 year. Myxobolus colossomatis and Henneguya piaractus were found in the internal organs and gills, respectively. The combined incidence of parasitism by both myxozoa was 97.3% in pacu (Piaractus mesopotamicus), 33.3% in hybrid tambacu (Piaractus mesopotamicus x Colossoma macropomum), 5.6% in tambaqui (Colossoma macropomum) and 0% in carp (Cyprinus carpio). Pacu was the most susceptible fish and was parasitized 79.2% in the gills, 66.7% in the kidney and 50% in the spleen. Histopathological evaluation of the gills showed hemorrhages, inflammatory reaction with mononuclear cells and fibroblasts and hyperplasia of basal and goblet cells