Piranhas are feared freshwater fishes commonly found in the waters of southern Venezuela to the north of Argentina. At present this species is a favourite domesticated article of our aquarists. The authors describe the histopathologic picture of a cutaneous lesion of the right hand thumb of a 60-year old piranha keeper who was bitten by this predatory fish. A firm node with increasing soreness gradually developed in the area of the lesion, and after 7 months the symptoms of the carpal tunnel syndrome were also present. Granulomatous foci – some sarcoid-like, others with central necrosis – were permeated with fibrinoid substance. Epithelioid granuloma cells with huge incorporated multinuclear elements were covered mainly by T-lymphocytes. Ziehl-Neelsen stain did not prove the presence of diagnostic acid-fast rods. Only in some macrophages rare acid-fast spheric microstructures were present in the cytoplasm. Both the local dermatologic finding and histological examination gave evidence that the skin was infected with atypical mycobacteria – swimming pool granuloma.

        Key words: piranha injury – granulomatous inflammation – swimming pool granuloma – atypical mycobacteriosis