The article presents results of analysis of distribution of Pacific cod in the Southwestern Bering Sea on the data of bottom trawl surveys 2000–2020 in different hydrological periods (spring, summer and autumn). Density and dynamics of the distribution by depth ranges and size composition of this species were analyzed. Assumptions about nature of Pacific cod migrations in analyzed area are formulated.

Species composition and structure of ichthyofauna of the Langeri River, one of the largest rivers in Northeastern Sakhalin Island and a significant reproductive area for Pacific salmon, are described. Sixteen fish species and one species lampreys were found in the river. The basis of fish community of the river are anadromous fish – 13 species, represented preliminary by Salmonidae family members (8 species). Nonmigratory fish are represented by three species belonging to families Leuciscidae, Gasterosteidae and Nemacheilidae. One invasive species, the rainbow trout Parasalmo mykiss, has been recorded in the ichthyofauna. New data on the biology of individual ichthyofauna species in the river are presented. History of formation of the ichthyofauna is discussed.

Data on the species composition and structure of catches, distribution and biological condition of the major commercial species in the summer period were obtained based on the results of Danish seine survey carried out in July 2024 in Terpeniya Bay. The species composition of catches includes 24 species of fish from 10 families. Flounders, Sculpins, and Cod fish were the most diverse. The most common were the yellowfin sole, Alaska plaice and the antlered sculpin. The catch per unit effort (CPUE) for a seining varied for the survey period from 1.0 to 15.4 tons, and was 7.0 tons averaged. The main body of the catches consisted of yellowfin sole. The contribution of this species into the total catches was estimated at 96.8%. The by-catch was dominated by Alaska plaice and starry flounder, great sculpin and antlered sculpin, which accounted for 1.1, 0.3, 1.0 and 0.5% by weight. The paper discusses the sources of uncertainty that arise when estimating marine fish stocks based on data of Danish seine surveys and possible limitations of the method in view of the effects of the uncertainty. Minimum estimates of the yellowfin sole total and commercial biomass in Terpeniya Bay in 2024 was respectively 36.8 и 34.8 thousand tons. The values indicate of a high level of stock abundance and provide indirect evidence of the growth of commercial populations in recent years.

An integrated approach based on histological, bacteriological, virological, parasitological, and hematological methods was employed between 2022 and 2024 to diagnostic of etymologically different diseases in juvenile Pacific salmon in salmon hatcheries of Kamchatka. Systemic mycosis of chum salmon was caused by the mitosporic fungi Phoma sp. A severe outbreak of trichodiniosis was linked to the toxic effect of surfactants, that reduced protective function of the fish skin. Increased mortality of Chinook salmon was a consequence of alimentary pathology. Results of the research demonstrate that integrated approach is crucial for identification of pathogen and, overall, for making diagnosis, treatment, and effective prevention of diseases in hatchery juveniles.

Data on the sex ratio of 6 species of Pleuronectidae off the Pacific coast of Kamchatka are summarized based on materials for 1955–2021 collected in the course of surveys and monitoring studies aboard fishing vessels. It has been established that as fish grow and age, the proportion of females among large individuals in older age groups increases, reaching 100%.