From October 1985 until July 1987, the seasonal dynamics of Rhabdochona denudata in its principal definitive host, the chub (Leuciscus cephalus), was studied in the Rokytná River (the Danube basin), Czechoslovakia. Prevalence (overall prevalence 77%) and intensity of infection (1-59 nematodes per fish) in the fish were high all year, with both abiotic and biotic factors influencing the fluctuations. Maximum values of prevalence (82-87%) were found in the fish with body length exceeding 20 cm; the mean intensity was highest in the size-group of fish 20-25 cm long, whereas its values gradually decreased in larger fish, this being due to the choice of food by fish of different size-groups. In contrast to the situation in other localities, an annual maturation cycle was not evident and egg-producing female nematodes were present in fish throughout the year. New infections in fish were most common in summer but occurred all year round. This life history pattern seems to be mainly due to the availability of infected ephemeropteran intermediate hosts during all seasons, in this case the nymphs of Ephemera danica, a species noted for its two-year development. In this locality, specifically not determined Rhabdochona larvae were recorded from the mayfly nymphs Ephemera danica (0.4%), Ecdyonurus aurantiacus (7%), and Caenis macrura (10%). The diet of the chub included mayfly nymphs at all seasons.

Institute of Parasitology Czechoslovak Academy of Sciences Ceské Budĕjovice

Trichopteran larvae (Insecta) as the intermediate hosts of Rhabdochona hellichi (Nematoda: Rhabdochonidae), a parasite of Barbus barbus (Pisces)