Comparative ecological analysis of the trematode fauna of fishes of the reservoirs cascade on the Kura River within Azerbaijan

In 2007-2022, in four reservoirs forming a cascade on the Kura River, 1243 fish of 30 species were examined for trematode infection using the method of complete parasitological dissection. For this purpose, 283 fish of 21 species were examined in the Shamkir Reservoir, 276 fish of 21 species in the Yenikend Reservoir, 341 fish of 25 species in the Mingechevir Reservoir, and 343 fish of 26 species in the Varvara Reservoir. As a result of the conducted research, 39 species of trematodes were found, of which 11 species parasitize in the lenses of the eyes, 9 species in the intestines, 4 species in the muscles and under the skin, one species each in the bloodstream, vitreous body, stomach, oral cavity and esophagus, urinary bladder, ureters, and kidneys, heart, brain, skin and fins, muscles and mesentery, walls of the swim bladder and kidneys, scales; 2 species at the metacercaria stage live in various tissues of fish, and in the adult stage – In the intestines of predatory fish. Among the found trematodes, 14 species use fish only as a definitive host, 23 species parasitize in fish only at the larval stage, completing their development in fish-eating birds, 2 species use various fish as a second intermediate host, and predatory fish as a definitive host. When comparing the studied reservoirs, it turned out that the greatest number of trematode species was found in fish from the relatively small Varvara Reservoir, where fish were infected with 27 trematode species. This is due to the fact that most of this reservoir is shallow, has a weak current and a lot of aquatic vegetation, which creates favorable conditions for the development of mollusks – the first intermediate hosts of trematodes, and also attracts fish-eating birds, which are the final hosts of many species of fish trematodes. Next in terms of the number of fish trematode species is the Mingechevir Reservoir, where 25 species were found in fish. It is the largest among the reservoirs we studied and has large areas with a slow current. In the fish of the Shamkir Reservoir, which is the second largest, 20 trematode species were noted, and in the relatively small Yenikend Reservoir, where there is a fast current, 17 species of fish trematodes were recorded. In each reservoir, the species composition of fish trematodes is richer in those areas where there is no fast current, overgrowing with aquatic vegetation is observed and fish-eating birds are present. It turned out that in reservoirs located close to each other, same species are found more often than in reservoirs located far from each other. Since previous studies, which were conducted by different authors in the 1950s, 1970s and 2000s, the species composition of fish trematodes in reservoirs that form a cascade on the Kura River has been significantly enriched. Among the trematodes found, 14 species are pathogenic for fish and 2 species are dangerous to humans.