Genetic differentiation of chum salmon in the basin of the Sea of Okhotsk is demonstrated. Eight microsatellite loci (Ssa20.19, One101, Oke3, Oki1b, Oki23, Ogo2G, Oke11, Ots102) were used as genetic markers. Four original genetic regions of chum salmon reproduction have been figured out: West Kamchatka and northern part of the continental coast of the Sea of Okhotsk, Sakhalin, Ithurup (the Kuril Islands), the Amur basin, where the part of juvenile fish was found as a result of genetic identification in the mixed aggregations in the early period of marine feeding. The resolution ability of the reference database was within the limits 74.9–94.6 %. It was demonstrated based on results of the genetic identification, that juveniles from West Kamchatka and northern part of the continental coast of the Sea of Okhotsk dominate in the northern part of the Sea of Okhotsk. Majority of individuals examined in the central zone of the survey area (54 %) was from the Kuril Islands. A number of juvenile chum salmon from the Amur River basin and Sakhalin were recorded at the stations in vicinity of Sakhalin coast.

   Existance of commercial snow crab aggregations for target fishing has been discovered in the Gulf of Shelikhov, the Sea of Okhotsk, based on the survey data for 2014 and 2021–2022. Sites of higher densities of snow crab have been figured. Analysis of sex ratio and size composition of the catches was made, and the catch values per an fishing effort and stock abundance of commercial males were estimated. In order to involve mentioned snow crab stock of the Gulf of Shelikhov, a ban for the fishing of snow crab has been recommended in the West Kamchatka subzone southward from 59°15´ N.

   Characteristics of feeding mechanisms, forage composition and methods of analysis of the diet of plankton crustacean are demonstrated based on reviewed and author’s data. Preferable forage species for the mass plankton crustaceans Cyclops scutifer and Daphnia galeata in the lake Azabachye were figured out using methods of population ecology. It is revealed, that reproduction of the cyclops and daphnia populations prospers due to Aulacoseira subarctica. In the periods of poor vegetation of the diatom the cyclops have been feeding on shell-less rotifers, and in particular years – on the diatoms of the genera Stephanodiscus. In the years of vigorous bloom of  Bacillariophyta the daphnias filter small cells of diatom (S. minutulus) or blue-green (Gloeocapsa sp.) algae. In case of suggested similarity in the forage organisms between small numbered Eurytemora kurenkovi and abundant C. scutifer, there was no competition observed between the copepods. The main forage component for predator Leptodora kindti was juvenile D. galeata. It is concluded based on the analysis, that intense competition between plankton crustaceans does not raise in the Azabachye Lake.

   While single mobile or immobile cells grouped into mucous “cloudy” colonies have been described in the life cycle of the haptophyta microalga Phaeocystis pouchetii, the first colonial bloom of this algae was detected on the east coast of Kamchatka (Avachinsky Gulf). The number of the colonies at the peak of the bloom in the coastal waters was 100 per liter. Such blooms of mentioned species in the European seas, in the Antarctic and some other coastal waters are often non-toxic. So, this phenomenon obviously requires study in monitoring mode.

   Based on materials collected during monitoring of bottom trawl fishing, the occurrence, some aspects of ecology and size composition of giant hookear sculpin Artediellus ingens were examined for the first time off the Middle Kuril Islands. It has been established that this species is a regular bycatch at the depths 250–488 m at the temperature of the near-bottom water layer of 1.8–3.9 °C. Most likely A. ingens belongs to mesobenthal ichthyocene. In the trawl catches, this species is represented by individuals of 10–19 cm TL. Comparison of the maximum body length with that of the other species of the genera Artediellus indicated this species is one of the largest.

   Based on materials collected in the course of angling in Uzovskaya Inlet, new data on the body length and weight of Platichthys stellatus were obtained, and information on the diet of the species is presented. Analysis revealed medium-sized individuals in the composition of catches. Their diet consisted of juvenile fish, gammarids, Pacific sand lance and shrimps.