This study was carried out to investigate the fish community in Osinmo Reservoir, Ejigbo, Osun State, Nigeria for parasitic helminth infections, and to determine the prevalence, intensity and seasonal variations of parasites in the fishes. Fish collection was carried out once a month from March 2013 to February 2014. The fishes caught were kept in open plastic buckets in water obtained from the pond. They were transported directly to the laboratory and examined for parasites within an hour of being caught, using standard laboratory procedures. 417 fish specimens belonging to nine species, Clarias gariepinus (11), Heterotis niloticus (12), Hepsetus odoe (41), Malapterurus electricus (7), Mormyrus rume (40), Oreochromis niloticus (41), Parachanna obscura (79), Sarotherodon galileus (9), and Tilapia zilli (177), were caught and examined. Five of the fish species were infected and five helminth species were recovered from them. The helminths include metacercaria of a trematode Neascus sp. Found in O. niloticus (2.4%), and four nematodes, Procamallanus leavionchus recovered from C. gariepinus (27.3%), Rhabdochona congolensis from Heterotis niloticus (33.3%), Ascarpos strongylina found in two fish hosts, Parachanna obscura (8.9%) and Hepsetus odoe (2.4%) and an unidentified nematode larva in H. odoe (2.4%). In all the fishes, the juveniles were uninfected. Among the adult fishes, prevalence was usually significantly higher among the males than the females (P<0.5). Fishes of higher standard lengths also consistently had significantly higher prevalence of infection than the ones with lower standard lengths (P<0.5). The mean intensity of infection varied from 3 for Neascus sp. in Oreochromis niloticus to 9 for R. congolensis in Heterotis niloticus. Males generally carry more worm burden than females. Fishes of lower standard lengths tend to carry higher worm burdens except in C. gariepinus where fishes of higher standard lengths are more heavily infected. The nematode, Procamallanus leavionchus, occurs only in the dry season while R. congolensis and the trematode Neascus sp. were found only during the wet season. A. strongylina was found in H. odoe only during the wet season while the worm occurs in P. obscura in both wet and dry season.