THE STUDY OF WHITEFISH (COREGONIDAE) SPAWNING AREAS IN THE GULF OF THE OB’ BAY
The results of the survey of whitefish (Coregonidae) spawning grounds in the Gulf of the Ob’ river are discussed in the article. The studies were conducted in 2013-2015. The aim of this work was to study the success of whitefish embryogenesis in conditions of the Ob’ Bay. In addition, one of the objectives of the study was to determine the spawning grounds of residential whitefish forms of Siberian whitefish (Coregonus lavaretus pidschian). However, during the study only eggs of whitefish (Coregonus sardinella) were discovered. The brief characteristics of fish fauna, features of fish seasonal distribution, dynamics of fish population and maturation, density and distribution of eggs, as well as the conditions of egg development are given in the article. The low selectivity of vendace to spawning substrate is noted. The eggs of this species were found even on silty soils including the depth more than 8.5 m. Different survival of vendace eggs, depending on the concentration of dissolved oxygen is analyzed. The high mortality of eggs in areas exposed to hypoxic water was detected. Overall survival does not exceed 5%. However, the success of embryogenesis is determined mainly by the relatively small sizes of the eggs due to the lower rate of metabolic processes. The worst conditions for reproduction of whitefish in the Gulf in compare with the Ural tributaries of the Ob were marked. The adaptive benefits of embryogenesis and life cycle of vendace in compare with other whitefish species are emphasized.