Summary:

maturation of the acanthocephalan Neoechinorhynchus rutili in its definitive host, the barbel (Barbus barbus), was studied in the Jihlava River (the Danube basin), Czech Republic. The parasite occurred in barbel throughout the year (overall prevalence 84% and intensity of infection 1-533 [mean 25] acanthocephalans per fish), but there were distinct seasonal fluctuations in prevalence and mean intensity values: prevalence attained 100 % in February and March, whereas its lowest value was recorded in July; the lowest values of mean intensity occurred in July-August. Both preva-lence and mean intensity values distinctly increased with the body length of hosts. The parasite exhibited a distinct annual maturation cycle when egg-producing females were present mainly in the spring and summer (May-July) and, at a lesser extent, also from December to April of the next year. The seasonal maturation of N. rutili appears to be induced principally by the temperature regimen in the locality. N. rutili cystacanths were recovered from larval Sialis lutaria (Megaloptera) (prevalence 6%)