Confirmation of the hosts involved in the life cycle of an acanthocephalan parasite of Anguilla anguilla (L.) from Lake Piediluco and its effect on the reproductive potential of its amphipod intermediate host

A total of 37 European eels, Anguilla anguilla, collected from Lake Piediluco, Central Italy, and measuring 35 to 75.5 cm in total length (mean±1 SD, 56.41±10.89 cm) were examined, and their acanthocephalan infections assessed. Thirty-two (86.49%) eels were infected with Acanthocephalus rhinensis (mean±1 SD, 67.38±65.16; range, 1–350), a species that, purportedly, can be discriminated on the basis of a characteristic band of orange–brown pigmentation encircling the anterior end of the trunk. This feature, however, was not seen on any of the A. rhinensis specimens that were removed, either attached to the gut wall or free within the gut lumen, from infected eels. Approximately 40% of the eels were coinfected with the dracunculid swimbladder nematode Anguillicoloides crassus, while a single eel was also coinfected with eight specimens of a second acanthocephalan, Dentitruncus truttae. From the stomachs of two eels, 109 intact and partially digested specimens of amphipod Echinogammarus tibaldii (Pinkster & Stock 1970) were recovered, 16 (14.6%) of these were infected with one to two cystacanths of A. rhinensis per host. From a sample of 850 E. tibaldii taken from the peripheral lakeside vegetation, 102 (12%; sex ratio, 1:1) gammarids were infected with one to two A. rhinensis cystacanths. Unparasitised ovigerous female E. tibaldii specimens had significantly higher numbers of eggs in their brood pouches compared with their infected counterparts (t-test, P<0.01).