On the biology of Dichelyne (Cucullanellus) cotylophora (Ward &Magath, 1917) (Nematoda, Cucullanidae) in perch (Perca flavescens) from Lake Erie, Ontario

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Abstract
Eggs of Dichelyne cotylophora embryonate in freshwater. There is one moult in the egg and a second moult when the egg hatches. Third stage larvae were not infective to perch or invertebrates (copepods, oligochaetes). However, these larvae were experimentally transmitted orally to small cyprinid fish in which they developed to the fourth larval stage and became encysted in the liver. It is hypothesized that prey fish act as intermediate hosts for this parasite. High prevalence of the parasite in large, piscivorous perch from Lake Erie supports thisliypothesis. In addition a histiotrophic stage of development occurs in the fish intermediate hosts rather than in perch. In other cucullanids studied, the life cycle is primarily monoxenous with a histiotrophic stage of development in the one host. Annual changes in prevalence, intensity, and worm development were followed in adult perch from Lake Erie. Worms are acquired in late summer, fall, and winter, but most larvae acquired at this time do not develop past the fourth larval stage until the following spring. Worms rapidly develop into adults in the spring and females begin to produce eggs in early summer. These adults disappear in late summer.