Occurrence of Pomphorhynchus laevis Müller 1776 (Acanthocephala) in Silurus glanis (L.) from the River Po.

The sheatfish, Silurus glanis (L.), from the terminal part of River Po was examined for the presence of helminth parasites. Of 182 S. glanis specimens, 95 (52.2%) were infected with the acanthocephalan Pomphorhynchus laevis. Mid-gut followed by fore-gut appeared to be the most infected portions of host alimentary canal. In 45 sheatfish of total length < or = 40 cm, specimens of P. laevis were found encapsulated in mesenteric and peritoneal tissues. A comparison between light and electron microscopy on features and stages of testis development in both encapsulated male P. laevis and intestinal male parasites showed that the encysted acanthocephalans were immature; mature spermatozoa were rarely found within the testis of worms from the alimentary canal. Among extraintestinal P. laevis specimens, the presumable eversion of parasite praesoma was observed and described. The results of the present survey suggest that small-size individuals of S. glanis could be used as paratenic host by P. laevis during its life cycle in the study area.