Outbreak of Infection by Piscinoodinium pillulare and Trichodina spp. in Tambaquis (Colossoma macropomu), Pirapitingas (Piaractus brachypomus) and Tilapias (Oreochromis niloticus) in the Federal District, Brazil

Background: Piscinoodinium pillulare is a mandatory mastigophore protozoan with no parasitic specificity, and an important ectoparasite of tropical and temperate psiculture. This parasite is responsible for serious health problems in Brazilian native fish. Another important pathogenic protozoan in psciculture belongs to the genus Trichodina spp., which is commonly found on the surface of fish, gills, fins, and integument. The aim of the present study was to describe an outbreak of P. pillulare andTrichodina spp. in three species of fish intensively created, emphasizing the anatomopathological and epidemiological aspects.Cases: Five animals were necropsied, among them three tambaquis (Colossoma macropomu), one pirapitinga (Piaractus brachypomus) and one tilapia (Oreochromis niloticus) from an intensive psciculture in the Federal District. Out of 1500 fishes, 18 (1.2%) became ill and died. It was reported that the animals showed decreased feed intake, discomfort, dyspnea, opercular movements, red skin lesions and consequent death. In the direct examination of scraping of the body surface of a fish, preparedbetween lamina and coverslip, a ciliated ectoparasite, with a circular bell shape, measuring approximately 20-180 μm, adhered, with morphology consistent with Trichodina spp. was evidenced. During necropsy, fragments of different organs were collected and fixed in 10% formalin, routinely processed for histology, embedded in paraffin, cut to five microns thick and stained with hematoxylin and eosin (HE). Macroscopically, there were pale scaly areas in the medial-lateral regions, moderate increase amountof mucus with brown to green lumps on the body surface, partial loss of the fins, swollen gills with whitish mucus and multifocal hemorrhagic areas on the skin and between the scales. Microscopically, moderate multifocal lymphoplasmocytic branchitis was observed with cell hyperplasia and fusion of secondary lamellae associated with trophons (protozoa), consistent with P. pillulare.Discussion: The diagnosis of infection by P. pillulare and Trichodina spp. in this study was based on the epidemiological and clinical-pathological findings. Regarding the first ones, we highlight the variety of fish species affected. P. pillulare is an example of a commensal parasite present on the substrate of culture tanks, and exerts a type of non-obligatory parasitism that uses the fish as a substrate for its fixation under favorable conditions. In this case, only Trichodina sp