[The causes of the formation of an intensive focus of triaenophoriasis in the upper Tuloma River reservoir].

Observations on the Triaenophorus crassus invasion in Coregonus lavaretus and Esox lucius were carried out in the period of 1984 to 1989 in the upper Tuloma River [correction of Verkhnetulomsk] water reservoir and Pechozero water body (the Pecha River) which form a common basin. Significant differences were noted in the infection rate of fishes with this parasite in the above water bodies. In Pechozero, where there are preserved natural conditions and therefore an ecological equilibrium in the host-parasite system, T. crassus is not abundant and the infection rate of C. lavaretus and E. lucius with this parasite is low. In the upper Tuloma River [correction of Verkhnetulomsk] water reservoir, due to the dropping out of the amphipod group of benthos from the biocoenosis of the water body, there has been formed a close ecological connection between copepods, C. lavaretus and E. lucius that resulted in the increase of T. crassus and gave rise to Triaenophorus infection of C. lavaretus here.