Morphobiological specific features of the river and lake forms of chum salmon Oncorhynchus keta (Salmonidae) on the southern Kuril Islands

Morphobiological differences between chum salmon Oncorhynchus keta dwelling in rivers and lakes on the Iturup and Kunishir islands are shown. The differences between chum salmon of different islands are reduced mainly to the interpopulation variation in growth determined mainly by the action of ecological factors. First of all, these are differences in the rate of growth and the number of sclerites in the first annual zone of the scales growth related to specific features of feeding in the area subjected to the action of different currents. The differences between the river and lake forms of chum salmon are, to a greater extent, determined by the action of selection according to body sizes and production of different amounts of eggs by females.