Biological characteristics of lower Amur grayling Thymallus tugarinae (Salmoniformes: Thymallidae): 3. reproductive biology

We discuss peculiarities of the reproductive biology of lower Amur grayling Thymallus tugarinae. The sex ratio in most of the studied samples was close to 1 : 1, but sometimes it might differ due to various reasons. Females dominated among the specimens entering the first reproduction period; the rate of females decreased in the fish older than 5 years. Maturation was usual in fish that reached 20-cm body length, which referred to the age 3+. The males became mature a year after the females of the same age in a half of the studied rivers. Absolute fecundity, egg size and weight, as well as gonad-somatic index, correlated positively to the age of the fish, its body weight, and length. The lower Amur grayling spawned from the end of April through the last decade of May at the water temperatures exceeding +6°C in the downwelling areas located upstream the riffles, on the small-size gravel bottom sediments, at the depths of 0.8 m and less, where the current velocity was less than 0.7 m/s. The spawning grounds in the main riverbed and tributaries of the lower stream of the Anyui River comprised 426.3 ± 148.6 m² per km², or 0.32 ± 0.11% of the water-surface area.