Dynamics of the least cisco Coregonus sardinella (Valenciennes, 1848) (Salmoniformes, Salmonidae) infected with Triaenophorus crassus (Plathelminthes, Cesto

Abstract

The ecosystem transformation that occurred upon the regulation of the Kureyka River to create the Kureyskoye Reservoir (66°56′47″ N, 88°20′33″ E) (Yenisey River catchment) has profoundly altered the communities and led to the formation of a seat of triaenophoriasis – a disease induced in fish by the cestode Triaenophorus crassus Forel, 1868. The least cisco, Coregonus sardinella Valenciennes, 1848, which has formed a population with unique biological characteristics in the Kureyskoye Reservoir, was used as the case for studying the prevalence and abundance distribution of T. crassus plerocercoids. The helminths were found in fish of all age groups, with prevalences varying from 27.6% in young-of-the-year (0+) to 96.6% in fish aged 4+. In fish infected at high intensities, most plerocercoids were situated freely in the musculature, not encysted in connective tissue. The distribution of plerocercoids among hosts in yearlings proved to be random (fitting the Poisson distribution), becoming aggregated from the age of two years (best approximated by the negative binomial distribution). Infection intensities grow exponentially with fish age, apparently becoming the main cause of elimination of older age groups. The hypothesis that the infection affects fish growth rates in the studied population was not supported. In this Arctic reservoir, a reduction in the trophic level and, hence, a decline in the T. crassus infection in the least cisco can be expected no earlier than 50 years after the impoundment.