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During the fish feeding studies in the Obutanai River (Sakhalin, Nevelsk district) in the time of juvenile salmon migration in May 2021, the pink and chum juveniles were found in stomach of white-spotted char (weight 72.3, 55.7 and 73.9 g) in the number of 21, 35 and 51 specimens, respectively. Among them, there were 3, 4 and 8 pairs of conjoined twins of pink salmon, obviously preyed recently and practically at the same time. It can be assumed that the conjoined twins of pink salmon were presented on the feeding grounds of char in significant numbers and developed synchronously with ordinary juveniles, so they were able to join the downstream migration.

Results of cherry salmon juveniles rearing at Reidovo fish farm on Iturup Island during two annual cycles of cultivation are analyzed. Different variants of the breeders selection, feeding, preventive treatment, and release were tested. The breeders were caught in the river mouth and near the fish farm. Mass mortality of young fish in the first and second years was avoided by decreasing of their density and other preventive measures. Minced fish was used as a food for them that is less expensive in compare with a combined fodder. The best diet for the second year of rearing was the minced pink salmon with the daily ration of 2 % of the juveniles body weight; it provided a significant decrease of mortality and enhanced their growth. After 2-year rearing, percentage of females, anadromous males, and dwarf males was 42.1, 36.3, and 21.6 %, respectively. Their weights were similar, though a group of fast-growing males was found among the dwarfs. The mass of ovaries varied from 13 to 46 mg in close dependence on females’ body weight (r = 0.81). Before the release, the ovaries of all females contained oocytes of similar size (varied in 2–4 times) at the final stage of previtellogenesis. Number of the oocytes per transverse section varied from 4.7 to 32.3, on average for 5 cuts and their diameter varied from 164.3 to 279.2 mm and did not correlate with the females body weight. The mass of dwarf males’ testes varied from 14 to 488 mg in dependence on their body weight (r = 0.78). The elder oocytes of females would mature in a year, and majority of dwarf males would reach the maturity in autumn of the current year.