LIFE-HISTORY OF THE NEMATODE RHABDOCHONA-HELLICHI, A PARASITE OF THE BARBEL IN THE JIHLAVA RIVER, CZECH-REPUBLIC

From April 1992 until June 1993, the seasonal dynamics of Rhabdochona hellichi (Sramek, 1901) in its definitive host, the barbel (Barbus bar bus), was studied in the Jihlava River (the Danube basin), Czech Repub lic. The parasite occurred in barbel throughout the year (overall prev alence 93% and intensity of infection 1-1384 [mean 78] nematodes per f ish), but there were distinct seasonal fluctuations in prevalence and mean intensity values associated with the parasite's seasonal cycle of maturation. Prevalence was very high (usually 100%) during most month s of the year, while lowest values were recorded in August and October . The highest values of mean intensity occurred in April. Both prevale nce and mean intensity values increased with the body length of the ho sts. The parasite exhibited a distinct annual cycle of maturation with egg-producing females present only from June until August, whereas la rvae occurred in barbel mostly from September until April of the next year. Trichopteran (caddis-fly) larvae of the genus Hydropsyche (H. an gustipennis and H. pellucidula) were found as natural intermediate hos ts of R. hellichi (prevalence 4%, intensity 1-10 nematode larvae). The strictly seasonal maturation of this nematode may be associated with the temperature regime in the locality and seasonal cycles of maturati on of its intermediate hosts.