Abstract: Trichodinids are important freshwater fish parasites in Brasil, but nothing is known about the species. This study describes Trichodina compacta Van As and Basson (1989) (Protozoa: Ciliophora: Peritrichia) from Nile tilapia (Oreochromis niloticus) cultured in fish ponds situated in three regions of Santa Catarina State, Brazil from October 2004 through June 2005. Wet smears of the skin and gills prepared in the field were air dried and impregnated with Klein’s dry silver impregnation method and Giemsa’s solution. From a total of 146 examined fish, 36 were parasitized on the skin, 14 in the gills and 33 on the skin and gills. The mean diameter of the body of this ciliate was 50.8+8.0 μm, adhesive disc 32.8+4.7 μm, denticulate ring 21.9+3.1 μm provided by 17 (15 to 19) denticles with central circle 8.5+1.1 μm in diameter. It differs from the original description of T. compacta in having shorter central area of adesive disc, smaller diameter of adhesive disc and number of denticles, but greater length of denticle and ray. In spite of these differences, the denticles morphology and its position in relation to y and y+1 axes from the original description this is not sufficient to create a new species. Trichodina truncata Ghiraldelli 2005 is therefore another population and synonym of T. compacta.