Japanese gill net fishery of walleye pollock in the Kunashir Strait, also well-known as local spawning grounds of this species, has been carried out in the eastern (Russian) part for more than 20 years. The results of the fishery allow us to consider general trends in the long-term changes of the local stock in mentioned dynamic and still underexamined area on the border of the Sea of Okhotsk and the Pacific Ocean. The use of a large series of standardized catch per effort as an index of stock biomass indicates specific dynamics of walleye pollock stock biomass in the Kunashir Strait, different from the behavior in the adjacent ocean waters of the southern Kuril Islands. On the background of a long-term trend of decreasing catch per effort in the Kunashir Strait, the CPUE in the ocean waters of the islands, as well as in the southern part of the Sea of Okhotsk, demonstrates opposite trend of increase of this parameter.

   Data on the biological structure of flounder species in the northern part of the Sea of Okhotsk based on samples collected in 2002–2019 are given. It is shown that the conception developed on literature sources (Моисеев, 1953; Фадеев, 1987; Борец, 1997) that flounders in the northern part of the Sea of Okhotsk are small-sized species living in extreme conditions, does not confirm our data. The maximum size and age of the flounders in examined area are comparable or even exceed those of similar species from the adjacent areas of the Sea of Okhotsk and, in general, the North Pacific. Data on the temporal dynamics of their biological parameters are given.

   Information on the fish parasite species revealed in the Penzhina and Talovka Rivers and Penzhina Bay of the Sea of Okhotsk (Northwestern Kamchatka) ordered systematically for the first time is presented in this paper. Hosts, infection rates, localization, and author of finding are listed for each parasite species. The fish parasites of the Penzhina River basin included 114 species from 13 classes, 22 orders, 39 families, 61 genera, and 27 of them were recorded for the first time, while new hosts were indicated for 23 species.

   Comparative analysis of feeding in the lower part of the Pymta River (West Kamchatka) is carried out for juvenile Pacific salmon individuals of different age representing four species with a short or long freshwater period of their life cycle (chum salmon Oncorhynchus keta, sockeye salmon O. nerka, coho salmon O. kisutsch and Chinook salmon O. tschawytscha) for the period from May to September in 2019–2020. Spectra of food, stomach fullness indices and degree of food similarity between juveniles of different species and age classes are demonstrated. The feeding in all mentioned species was biotop-dependent. There were frequent changes in the composition of the forage consumed in the course of observations of Pacific salmon juveniles in the Pymta River basin, and the indices of stomach fullness varied extensively. The results of the analysis indicate extensive trophic adaptability in juvenile Pacific salmon in the ecosystem of the Pymta River.

   Analysis of biometric data of juvenile sockeye salmon caught during the run to sea in the channel from Nachikinskoe Lake was carried out in order to clarify the question of the minimum possible number of sclerites on the scales to the 1st annual ring. For the first time, the study of the features of the scale structure of juvenile sockeye salmon of different ages was carried out. The differences revealed between groups of individuals of different age categories are highly reliable not only in weight and length, but also in the total circuli number in the freshwater zone and circuli number to the first annual ring (6.0 ± 0.1 in yearlings, 3.9 ± 0.3 in two-year-olds); physiological explanation for these differences is proposed. On the basis of the scleritograms constructed, a comparison of other features of the scale structure of the juvenile migrants of different ages was carried out. The key characteristics obtained are recommended as clarifying criteria in reading the freshwater age of juvenile sockeye salmon in Nachikinskoe Lake.

   The first data on the morphometry of the Nalychevo Lake are obtained from the echo sounding survey accomplished by A. S. Nikolaev in 1994 and bathymetric scheme constructed on the results; morphometric characteristics of the lake are calculated.