On biology of Kaluga sturgeon Acipenser dauricus (Acipenseridae) from the Viakhtu River (Northwestern Sakhalin)

Data on catch of three specimens of Kaluga sturgeon Acipenser daurucus in the channel part of the Viakhtu River (Sakhalin Island) are first presented; their morphometric indices are provided. According to data of histological study, females with a length of 121–127 cm and a weight of 12–20 kg have ovaries at III early stage of maturity. It was demonstrated that food resources of the Viakhtu River can provide spawning of immature individuals of Kaluga sturgeon in June–July. It was proved that the range of Kaluga sturgeon includes, as minimum, one of the rivers of the northwestern part of Sakhalin Island.