During November–December 2003, 44 fishes belonging to 6 endemic cichlid taxa (Amphilophus citrinellus “short”, Amphilophus citrinellus “chancho”, Amphilophus amarillo, Amphilophus sagittae, Amphilophus xiloaensis, and Parachromis managuensis) and 8 specimens of Gobiomorus dormitor were collected from 2 crater lakes in Nicaragua: Lake Apoyo and Lake Xiloá. Helminthological examination revealed 8 nematode species, 3 adults and 5 larval stages. Rhabdochona (Rhabdochona) kidderi was the only nematode present in both bodies of water; Procamallanus (Spirocamallanus) rebecae and Paracapillaria teixeirafreitasi teixeirafreitasi were restricted to Lakes Apoyo and Xiloá, respectively. Procamallanus (S.) rebecae and Contracaecum sp. type 2 were the most prevalent and abundant species found in Lakes Apoyo and Xiloá, respectively. Specimens exhibited morphometric variability in comparison to nematodes collected from fishes in southern Mexico. All nematode species have been previously reported from the same or phylogenetically related host species in freshwater habitats in southern Mexico and the Atlantic coast of Nicaragua. All species represent new geographical records, whereas nematodes from A. c. “short”, A. c. “chancho”, A. sagittae, A. xiloaensis, A. amarillo, and Spiruridae gen. sp. and Contracaecum sp. type 1 in G. dormitor are new host records. The nematode fauna of cichlid and eleotrid fishes from the Atlantic and Pacific coasts of Nicaragua is similar to that from southeastern Mexico.