Observations on the occurrence and maturation of Rhabdochona anguillae (Nematoda: Rhabdochonidae) in the Sousa River, Portugal

Data on the seasonal occurrence and maturation of Rhabdochona anguillae Spaul, 1927 in its definitive host, the European eel, Anguilla anguilla, from the Sousa River, northern of Portugal, are presented. Monthly samples were taken from November 1998 to October 1999. A total of 326 fish specimens were examined. R. anguillae occurred all the year round (overall prevalence and mean intensity 54 % and 3, respectively), not showing pronounced seasonal cycles of occurrence or intensity. The main period of maturation of the nematodes was spring and early autumn, but gravid females with mature eggs in the uteri were present throughout the year. Although occurring during all the year, new infections in eels were most common in the end of spring. Unidentified Rhabdochona larvae were recorded from the caddis fly larvae, Hydropsyche spp. (prevalence and intensity of 29 % and 1 to 34, respectively).