Ecological and faunistic analyses of the trematodes of the Little Grebe (Tachybaptus ruficollis (Pallas, 1764)) in Azerbaijan

The research was conducted from 1998 to 2019 at the nine water bodies of Azerbaijan. During the study, 94 individuals of the Little Grebes (Tachybaptus ruficollis (Pallas, 1764)) were examined by the method of complete helminthological dissection. As a result, 12 trematode species belonging to one order, seven families, and eight genera were found: Patagifer bilobus, Petasiger megacantha, P. skrjabini, Echinochasmus coaxatus, E. dietzevi, E. mordax, Mesorchis pseudoechinatus, Cryptocotyle concavum, Metorchis intermedius, Eucotyle cohni, Strigea falconis, Hysteromorpha triloba. Of these, three species (Petasiger megacantha, Echinochasmus coaxatus and E. dietzevi) are specific grebe parasites, while the others infect various waterfowl. Except for Strigea falconis, whose cercariae penetrate actively into the bird’s body and transform into metacercarie, all the trematode found are ingested by the birds and mature in their intestine. The grebe, as a fish-eating bird, is infected with six trematode species (Patagifer bilobus, Petasiger megacantha, Mesorchis pseudoechinatus, Cryptocotyle concavum, Metorchis intermedius, Hysteromorpha triloba) that parasite in fish at the stage of metacercaria. Other species use aquatic invertebrates as second intermediate hosts. We established that species diversity of the grebe trematodes depended on the reservoir size and the richness of its hydrofauna, increasing with the increase of both factors. The differences between the faunas of grebe trematodes in various water bodies depended on the distance between them and the similarity of their living conditions. Seven grebe trematode species (Petasiger megacantha, P. skrjabini, Echinochasmus coaxatus, E. dietzevi, Cryptocotyle concavum, Metorchis intermedius, Eucotyle cohni) belong to the northern group of helminthes, while the five species (Patagifer bilobus, Echinochasmus mordax, Mesorchis pseudoechinatus, Strigea falconis, Hysteromorpha triloba) are ubiquitous. Southern trematode species were absent from the examined birds. Presumably, this can be explained by the dominance of grebes from northern populations wintering on the water bodies of Azerbaijan.