Monogenean assemblages and the apparent transmission capability of monogeneans between related fish species: an experimental study.

Gyrodactylid monogeneans are considered to be the most invasive fish parasites. They are omnipresent on teleost fishes and host change might play a crucial role in their biology. In the present study, related fish species were kept in single- or mixed-species groups to test the ability of Gyrodactylus species to change their host fish under experimental conditions. The first group included two percid fish species, perch Perca fluviatilis L. and ruffe Gymnocephalus cernuus (L.), and the second group two cyprinid species, roach Rutilus rutilus (L.) and minnow Phoxinus phoxinus (L.). A total of 4,182 specimens of 19 monogenean species belonging to five genera were observed, and eight species of Gyrodactylus were identified. There were three species of Gyrodactylus found on roach and six species on minnow. Gyrodactylus vimbi parasitized both cyprinid fish species and was the only species that increased in intensity during the experiments and also assumed to transmit from minnow to roach, while the other recorded host change case, Gyrodactylus macronychus, was represented by a single individual that transmitted from minnow to roach. Gyrodactylus rutilensis and Gyrodactylus pannonicus remained on their original hosts (roach and minnow, respectively). Gyrodactylus cernuae was the only species observed on both ruffe and perch, but ruffe appeared more susceptible to this parasite. Most of the gyrodactylids observed on roach and minnow were situated on the fins, while gyrodactylids of perch and ruffe parasitized mainly the gill chamber and head.