Infestation of the Viviparus viviparus L. population of the Malaya Kokshaga River by the trematode parthenites and the carotenoid content in the tissues of mollusks

The paper presents the results of a long-term research (2001-2011) of the Viviparus viviparus L. population of the Malaya Kokshaga River, which is the 42nd left tributary of the Volga River and flows through the territory of the Mari El Republic. Density, biomass, sex structure and age structure of this population were the items of the investigation. The author defined the infestation of the gastropods by the trematode parthenites and the effect of parasites on the content of carotenoid pigments in the tissues of mollusks. A three-mark infestation scale was developed to determine the intensity of infestation. Throughout the whole study period, the infestation of V. viviparus by the trematode parthenites was consistently high. More than 50% of all individuals were infected by the larvae of various trematodes at all stages of development. Significant differences in the infestation of males and females were not registered. The author marked the influence of trematode invasion on the content of carotenoids. The infected individuals of both sexes in spring as well as in summer showed a higher content of carotenoids than uninfected ones. The V. viviparus population of the Malaya Kokshaga River was dominated by one year’s age individuals with a shell height of 18,0-25,9 mm. The sex structure of the V.viviparus population of the Malaya Kokshaga River was stable for the whole period of the research. The predominance of males or females in the population is insignificant. There are no significant differences in the number and biomass of V. viviparus over the years.