Colonization and Dispersal of Parasites

the Life History of Fish Parasitic Nematodes in Streams (Preliminary report)

Abstract

Commonly, parasites have no ways to migrate independently. Stream-dwelling organisms are often transported downstream in the water column. How do parasites migrate upstream and colonize other water systems in a mountain stream? The fish parasitic nematodes Rhabdochona denudata, R. coronacauda, and Cystidicoloides ephemeridarum were found in the upper reaches of streams in western Japan. They need two hosts to complete their life cycle: an ephemeropteran species as an intermediate host, and a freshwater fish as the definitive host. Interesting questions relating to their life history is why these nematodes need an intermediate host. One plausible ecological answer to the question is that the nematodes use the body of ephemeropteran nymph for nutrition, and the body of imago as a vehicle to migrate upstream. I studied the seasonal distribution of nematodes in mayfly nymphs to clarify the effect of upstream migration of imagoes from the viewpoint of maintaining riverine populations.