ACANTHOCEPHALANS IN WATERFOWLS OF LAKE BAIKAL

The purpose of this work was to clarify the species composition of acanthocephalans of Baikal waterbirds and to determine their relative abundance in modern environmental conditions. Ninety nine specimens of 13 species of waterfowls were studied by the method of special and complete dissection in Lake Baikal. Birds were studied according to the method given in the work by M. N. Dubinina. Three species of acanthocephalans were recorded: Polymorphus minutus (Goeze, 1782), P. acutis Van Cleave et Starret, 1940, and P. magnus Skrjabin, 1913. To assess the quantitative parameters of host infection, the following indices were used: prevalence of invasion (iP), intensity of invasion (iI, limits) and abundance (A). P. minutus was the most widespread species of acanthocephalans. Acanthocephalans are localized in the small intestine of birds. Polymorphae penetrate very deeply into the small intestine wall of the host. Unlike echinorhynchids whose proboscis penetrates only into the submucosa of the intestinal mucosa of fish, the proboscis and neck of polymorphids pierce the mucous and muscular membranes reaching the serous membrane. Tubercles are observed on the outer, serous side of the intestine that mark places of attached acanthocephalans. With a high number of definitive hosts, they can potentially exert a regulatory influence on the number of bird populations.