Hooked by the tongue: buccal parasitism of Moenkhausia spp. (Ostariophysi: Acestrorhamphidae) by Paracymothoa astyanaxi (Isopoda: Cymothoidae).

Parasite-host interactions are shaped by environmental and biological factors, leading to diverse host impacts ranging from tissue damage to physiological impairments. The Tocantins-Araguaia basin, particularly the Upper Rio Tocantins region, harbors remarkable fish diversity and endemism, making it a critical area for parasitological research. Here, we report the first record of parasitism by isopods of the genus Paracymothoa in Moenkhausia species (M. aurantia and M. goya) from the Upper Rio Tocantins basin. The parasites (Paracymothoa astyanaxi) were located in the buccal cavity and frequently associated with visible lesions, including tongue amputation, a known outcome of their trophic behavior. This finding contributes to the understanding of parasitic diversity associated with Moenkhausia and underscores the relevance of parasitological surveys in Neotropical freshwater systems. It also provides insights into local ecological pressures and supports the development of conservation strategies for endemic ichthyofauna in biodiversity-rich and ecologically sensitive areas.