This study aimed to investigate the presence of nematodes Spirocamallanus krameri and Contracaecum sp. in Hoplerythrinus unitaeniatus caught in a lake in the state of Pará, in northern Brazil, eastern Amazon region (Brazil). From 92 hosts, 83.7% were infected, and a total of 401 parasites were covered. There was a high prevalence of S. krameri, while the predominance was of Contracaecum sp. larvae. Both parasite species presented aggregated dispersion, and abundance of these parasites presented positive correlation with weight and length of the hosts. Morphological and morphometric data of third-stage larvae of Contracaecum sp. are described.