Pike Cannibalism, Paratenic Hosts and Trematode Life Span as Factors Influencing the Distribution of <i>Azygia lucii</i> in the Definitive Host Population

Abstract

The ratio of the body length of the trematodes Azygia lucii and the body length of pikes in the population of the Rybinsk Reservoir was studied. The material was collected in September–October from 2018 to 2021. A total 386 pike was divided into seven size classes according to body length (range 4.7–83 cm). The prevalence of A. lucii increased from 14.2% in underyearlings to 46.2% in pikes 9+. The distribution of the trematodes in all size classes was aggregated. The usual intensity of invasion was 1–3 trematodes in all classes; the proportion of fish with this intensity of invasion varied from 62.5 to 83.3%. A total of 259 worms were measured. The body length of the found worms ranged from 0.49 to 3.5 cm. The average length of A. lucii increased with host size from 1.39 cm in underyearlings to 2.39 cm in older pikes. The largest trematodes (3–3.5 cm long) were found in the largest pikes. Distribution/redistribution of trematodes in the pike population occurs due to pike cannibalism. Due to this, a group of trematodes is formed in large pikes, consisting of worms of different ages and sizes. An important role in the formation of such groups of trematodes is played by paratenic hosts. Their significance depends on their infection rate and the proportion in diet of pike in a particular reservoir. Features of the biology of A. lucii (large body size, short contact of trematodes with mollusks) suggest a long lifespan of marites.