Histopathological Assessment of Diseases in Ornamental Fish from 2019 to 2023 in Minas Gerais State, Brazil

The present study aimed to investigate the anatomopathological findings in ornamental fish from multiple sources, submitted to the diagnostic service at the Veterinary School of the Universidade Federal de Minas Gerais (UFMG) between 2019 and 2023. Macroscopic and histopathologic examinations were conducted, and the resulting data regarding disease processes were analyzed through a descriptive observational approach. A total of 635 ornamental fish were studied, with a predominance of exotic fish species. The fish were sourced from ornamental fish farms (37.00%; 235/635), shopkeepers (32.44%; 206/635), facilities (18.43%; 117/635), hobbyists (8.66%; 55/635), and wholesalers (3.46%; 22/635). Among the analyzed cases, 50.39% (320/635) presented relevant anatomopathological findings. The main categories of diseases detected were parasitic (56.25%; 180/320), bacterial (20.31%; 65/320), fungal/oomycete (7.50%; 24/320), viral (7.18%; 23/320), neoplastic (1.88%; 6/320), congenital (2.50%; 8/320), and metabolic (0.94%; 3/320). The main parasites found were unidentified digeneans (15.45%; 34/220), presumed Centrocestus formosanus (14.55%; 32/220), monogeneans (13.18%; 29/220), presumed Tetrahymena spp. (8.18%; 18/220), and presumed Epistylis (6.36%; 14/220). There were diagnoses of undocumented diseases in Brazil, such as the suggestive cases of Ichthyophonus spp. In addition, novel potential pathogen–host associations in the country were documented, such as Pleistophora sp. in Carnegiella strigata. This study presents findings that can contribute to determining disease frequency and identifying pathogens based on microscopic lesions.