Diet and intestinal helminths in a population of perch, Perca flavescens

Abstract

In 1967 and 1968 1310 Perca flavescens (Mitchill) were examined from Lake Opeongo, Ontario for changes in five diet categories and in incidence of eight intestinal helminths in relation to seasons, host size and sex. Male fish were less common than females and were smaller. A high proportion of fish (57.7 %) had empty stomachs, but of the four types of foods taken microcrustacea were high in spring, late summer and again in early winter; insects increased in summer with another peak in autumn; crayfish had a small peak in spring and a larger one in autumn; and fish were lowest in summer. Males ate more smaller foods (microcrustacea) than females, but females ate more larger foods (crayfish and fish); no sex difference was seen with regard to insects or empty stomachs. Male fish ate very few larger items, but females showed an increase in food size with increasing size of fish. There was no seasonality in incidence of fish free of all parasites, but two trematodes Bunodera sacculata Van Cleave & Mueller and B. luciopercae (Müller), and one cestode Proteocephalus pearsei La Rue showed seasonality with populations lowest in fish in summer; and one trematode Crepidostomum cooperi Hopkins and one nematode Dacnitoides cotylophora Ward & Magath showed seasonality with populations highest in summer. In addition one cestode Bothriocephalus sp., one nematode Spinitectus gracilis Ward & Magath and one acanthocephalan Leptorhynchoides thecatus (Linton) showed no seasonality, perhaps on account of the low incidence in the case of Bothriocephalus sp. and L. thecatus. No parasites were more common in males, but two (P. pearsei and L. thecatus) were more common in females. In both males and females, with increasing size fish, (i) fish free of all parasites decreased, but (ii) incidence of C. cooperi increased. Incidence of B. luciopercae, Bothriocephalus sp., S. gracilis and L. thecatus all increased with increasing size of fish only in females. The relationship between diet and incidence of intestinal helminths is discussed in the light of what is known of their life cycles. The exercise illustrates our ignorance of population ecology of fish parasites and the interactions of parasites and their host populations.