<jats:p>According to modern data, 260 species of parasites have been observed in Baikal fish, most of them have a simple life cycle (63.1%). The parasite fauna of introduced fish includes 48 species, including 15 specific ones that were imported from the mother reservoirs. The most ancient are the endemic simple parasitic systems of Cottoidea, which were formed as a result of prolonged isolation of their hosts in Lake Baikal (in the Pliocene, 2.5 million years ago).</jats:p>