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

Abstract

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 spp. was observed during the traditional evaluation of body surface and gills scraping, and histopathology was essential for the verification of the agent P. pillulare. Routine histopathological analysis may also provide a definitive diagnosis, observing the trophons attached to the gill filaments. Atrophy and fusion of secondary lamellae, which promote proliferative lesions in the gills associated with the interlamellar presence of parasites, are responsible for hypoxia, loss of balance and erratic movements. Although they were observed in a small number, Trichodina spp. are believed to be responsible, on a larger scale, for hemorrhagic lesions on the skin and between fish scales. These findings were similar to those of the literature, and the diagnosis of these parasites allows producers and technicians to adopt adequate treatment, as well as prophylactic measures that provide good environmental conditions in order to avoid economic losses.Keywords: fish diseases, protozoa, fish ectoparasites.