Unexpected Discovery of an Ectoparasitic Invasion First Detected in the Baikal Coregonid Fish Population

Abstract

The omul, Coregonus migratorius (Georgi, 1775), an endemic fish of Lake Baikal, is the main commercial species of essential economic importance for the extensive region of Eastern Siberia. Despite the continuous 250-year study of Baikal omul and intensive commercial fishing, neither fishers nor biologists have ever mentioned or found external annelid parasites in numerous omul catches. Targeted parasitological studies have also never detected these ectoparasites on the body of this fish. In this study, we present the first reliable information on the existence of specific annelid parasites infecting the pelagic population of Baikal omul and report a 4% infestation of spawners in the Selenga River, the largest tributary of Lake Baikal. We also obtained the main morphometric parameters of the infected fishes, the morphology of the unknown parasite and its feeding strategy. DNA-based analysis was applied to ascertain the taxonomy of the leeches and revealed no closely related taxa existing in international genetic databases (e.g., GenBank) to date. A maximum genetic identity of 89–91% was detected with European Caspiobdella fadejewi. The genetic distances in 9–11% of the substitutions from the closest relatives were very high for a reliable molecular identification of a taxon. The Selenga omul leech may represent a potentially new species and genus.