Ecological analysis of the fish cestode fauna of the mouth of Kura River

The research was conducted in 2014–2019 in the mouth of Kura River. A total of 334 fish specimens of 24 species were examined by the method of full parasitological dissection. As a result, 17 tapeworm species in two orders and eight families were found: Caryophyllaeus fimbriceps, C. laticeps, Caryophyllaeides fennica, Eubothrium acipenserinum, Bothriocephalus acheilognathi, Ligula colymbi, L. intestinalis, Bothriocephalus acheilognathi, Ligula colymbi, L. intestinalis, Proteocephalus filicollis, P. gobiorum, P. ocellata, P. osculatus, Siluritaenia siluri, Gryporhynchus pusillus, and Paradilepis scolecina. Of these, seven species are specific cyprinid parasites, two species are specific sturgeon parasites, two species are specific to sticklebacks, two species to catfish, and one species to gobies; the other three species parasitize in fishes of various families. The main organ of cestode localisation in the studied fishes is the intestinal lumen, where 11 worm species were found. In other fish organs (body cavity, mucous membrane of the anterior intestine, liver, mesentery, and intestinal walls), the number of tapeworm species ranged from one to four. One cestode species invaded from one to seven fish species. In the bream, we found six tapeworm species, while in the other fish species, from one to five. Among the cestodes found, 14 species infect zooplankton-eating fish and only three species (Caryophyllaeus fimbriceps, C. laticeps, Caryophyllaeides fennica) infect fish that feeds on benthic invertebrates. The largest trophic group was the benthophages; they hosted 12 cestode species. In the planktophages and predators, we found eight and seven tapeworm species, respectively. Predatory fishes like pike, asp, round and bighead gobies accumulate parasites from the bodies of their preys, consequently, their cestode fauna is the richest. Most recorded fishes are euryhaline. Nevertheless, due to the absence of typical marine forms among the found cestodes, we registered more tapeworm species in the fish occurring the highly desalinated area of the Kura mouth than in more mineralized water. Six recorded species (Caryophyllaeus fimbriceps, Bothriocephalus acheilognathi, Ligula colymbi, L. intestinalis, Digramma interrupta, and Paradilepis scolecina) are causative agents of fish diseases. Ligula colymbi and L. intestinalis, which have large plerocercoids, caused pathogenic changes in fish organisms. The other pathogenic species did not induce noticeable disorders. They are much smaller, and, thereto, had comparatively low invasion rate in the examined fish.