Metacercarial distribution of Apophallus brevis (Heterophyidae) in yellow perch (Perca flavescens) from the Heming Lake study area

Abstract

During a fish parasite survey in 1980 and 1981, 395 yellow perch (Perca flavescens) were removed from the Heming Lake study area (54°53′ N, 101°07′ W). Encysted Apophallus brevis metacercariae were found in the body musculature of perch from six lakes as well as the eye and body musculature of perch in Heming Lake. Species identity was confirmed with experimental infections in ring-billed (Larus delawarensis) and herring (Larus argentatus) gulls. No significant differences were found in prevalences or mean intensities of A. brevis metacercariae between male and female perch in Heming Lake. Prevalence levels remained high in most age-classes of Heming Lake perch and mean intensity differences were not significant for all ages beyond 1 year old. Slight variations from these Heming Lake results were found in other lakes. Prevalence levels of A. brevis in Heming Lake perch remained more or less constant during the open water seasons. Mean intensities dropped significantly from June to July and increased in August and October. Monthly fluctuations are probably the result of recruitment of the parasite and a loss of heavily infected hosts. The variance to mean ratios of A. brevis in perch from Heming, Home, and Demarch lakes showed that these parasite populations were overdispersed, and the distribution of each was found to fit the negative binomial. The authors question the use of variance to mean ratios or other statistics dealing with overdispersion in predicting loss or recruitment for all parasite systems.