Abstract
Evidence on morphology, biological characteristics, and ecological peculiarities of monocyclic, nonparasitic resident form of lamprey of the genus Lethenteron inhabiting the Amur River basin is presented for the first time. The studied sample includes mature individuals and three size groups of larvae. Maximum length and weight of larvae comprise 191 mm and 9.5 g, respectively; that of adult individuals is 182 mm and 8.2 g. Sex dimorphism was determined according to several characters, of them the most significant are anteanal and antedorsal distances, as well as the distance from the anus to the end of the body. Reproduction takes place at the end of May-beginning of June at the water temperature 13–15°C. At different spawning grounds, density of individuals averages 96–133 ind/m2; males are greater than of females by a factor of 1.5. The individual absolute fecundity is 1683 (1042–3166) eggs with a diameter of 0.83 (0.79–0.87) mm. The lamprey inhabits both the main channel of Angara (up to the inflow into it of the Kitoi River) and its tributaries.
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