Fifteen identified species and 13 genera, of endoparasitic helminths (Digenea, Eucestoda, Nematoda, Acanthocephala) were collected from 207 white crappie and 189 channel catfish June, 1967, through September 1968, from a 3,300-acre, turbid reservoir in northcentral Oklahoma. Differences in the prevalence and intensity of helminths from six reservoir collection sites were not statistically significant. Statistically significant differences in intensity and prevalence of certain helminth were found among different age classes of the hosts. Ontogenetic changes in the food habits of channel catfish, from a diet of invertebrates to fish, were apparently the reason for changes in the occurrence of many enteric helminths. The occurrence of some helminths, however, was independent of age. Changes relating to age in the crappie were limited to the occurrence of Posthodiplostomum minimum where multiple generations of metacercariae accumulate in older fish. These metacercariae occurred in significantly higher numbers in males. Otherwise the occurrence of parasitism did not differ significantly between the sexes. Seasonal differences in parasitism, heretofore rarely studied, were pronounced, reflecting changes in feeding, metabolism, and the reproductive cycle of the host, and the annual life cycle characteristics of the parasite. Some parasites, such as Dacnitoides robusta, were absent in the channel catfish in the winter but abundant in the summer. Conversely, proteocephalid tapeworms from the channel catfish were abundant in the winter and infrequent in the summer. Observations on the pattern of seasonal variation in prevalence and degree of infection of Posthodiplostumum minimum in the white crappie suggests that it may contribute to summer mortality of its host.