a b s t r a c tThe present study describes lesions caused by Kudoa sp. in the esophageal tissue of mapará catfishes (Hypophthalmus marginatus) collected from Cametá, Tocantins River in the northern Brazil. Fifty refrigerated H. marginatus specimens were dissected and tissue samples were for embedded in paraffin and stained with hematoxylin-eosi, Masson's trichrome and Giemsa. Pseudocysts of whitish color were observed in the esophagus region. The parasites had four valves and other morphological characteristics of the genus Kudoa. Microscopic analysis revealed lesions in the mucosa, submucosa, and muscular layers. The Masson staining highlighted the presence of myxosporean cysts in the cytoplasm of the muscular fibers, and marked fibrosis of the muscular and mucous layers. The macro and microscopic findings of the present study confirm the presence of necrotic esophagitis in H. marginatus associated with infection by Kudoa.