Copulation of Acanthocephalus anguillae (Acanthocephala)

A total of 114 specimens of brown trout, Salmo trutta Linnaeus, 1758, was sampled by electrofishing between October 1998 and July 1999 from the Ceresone stream (North of Padua, Italy). Over 63% of fish were infected with three species of helminth: a tapeworm, Cyathocephalus truncatus (Pallas, 1781), and two acanthocephalan species, Echinorhynchus truttae (Schrank, 1788) and Acanthocephalus anguillae (Muller 1780). On three occasions, in the fore-gut of three brown trout, three pairs of A. anguillae were found in copula. In all three cases, the male's bursa was fully extruded and firmly attached to the posterior region of the female. Cement was found inside the bursa suggesting that insemination had probably occurred. Eight female A. anguillae recovered in five other infected trout had attached copulatory caps.