ABSTRACT The Muscovy duck is a commercially important bird on the island of Marajó usually raised in a peculiar system that includes supplying fish viscera to the birds under semi-extensive farming conditions. This enables a risk of contamination and losses in the production of these birds, resulting from injuries caused by helminth infections, especially nematodes. The objective of this study was to evaluate the histopathological changes caused by nematodes of the genera: Eucoleus, Anisakis and Contracaecum. Thirty-three ducks with lesions in the esophagus and ventricle were analyzed. Histopathological exams showed a mild inflammatory infiltrate in the submucosa of the esophagus caused by the fixation of E. contortus and third stage larvae of Anisakis sp., and we recorded third stage larvae of Contracaecum sp. parasitizing the ventricle, this being the first record of this parasite in ducks in Brazil.