Duration of Embryonic and Larval Development of Chum Salmon Oncorhynchus keta (Salmonidae) on Sakhalin and Iturup Islands

The duration of embryonic and larval development of chum salmon Oncorhynchus keta under different temperature conditions was studied based on long-term data on the species breeding at three salmon hatcheries on the southeastern coast of Sakhalin Island and at three hatcheries on Iturup Island. The temperature conditions at each of them depended on the water supply system. The obtained results are fully consistent with the well-known general pattern of a slowdown in the development rate of Pacific salmons with a decrease in water temperature. At the same time, when comparing the corresponding data on salmon hatcheries from different regions, statistically significant differences were found both in the duration of embryonic–larval development of chum salmon in connection with water temperature (parallelism of regression lines) and in the rate of yolk resorption in larvae at similar temperatures. Despite the specific conditions of hatchery breeding, the revealed differences are quite explainable by the peculiarities of natural reproduction of the studied chum salmon groups. The results suggest a hereditary basis for the rate of embryonic and larval development of chum salmon, the genetic differences of which between the studied areas were previously identified. Consequently, differences in the development rates of chum salmon offspring during the freshwater period of life can serve as another criterion in addition to morphological, biological and genetic differences, on the basis of which ecogeographic units of the species are distinguished.