Comparative analysis of cetacean and fish species distribution in the Barents Sea is conducted on the data of joint Russian-Norwegian ecosystem surveys in August-October of 2005–2014. The number of observed minke whale (Balaenoptera acutorostrata), humpback whale (Megaptera novaeangliae), fin whale (Balaenoptera physalus), white-beaked dolphin (Lagenorhynchus albirostris), and harbor porpoise (Phocoena phocoena), as well as the acousticmeasured distribution density of fishes, as capelin (Mallotus villosus), polar cod (Boreogadus saida), herring (Clupea sp.), cod (Gadus morhua), haddock (Melanogrammus aeglefinus), saithe (Pollachius virens), blue whiting (Micromesistius poutassoumes), redfish (Sebastes sp.), norway pout (Trisopterus esmarkii), and fish fingerlings are summarized by the squares 50 x 50 km and maps of their distribution are drawn. A degree of overlapping between distributions of cetacean and fish species is estimated for each pair of species, as ratio of number of the squares where the species were presented together to total number of the squares where the species were found. Associations between cetaceans and their potential prey are determined by the methods of principal components and correlation analysis applied to the log-transformed data. Distribution of the widely distributed cetaceans, as minke whale and white-beaked dolphin, overlapped largely (up to 42 %) with many of studied fish species, therefore their possible predation on these species was significant. On the contrary, locally distributed cetaceans, such as harbor porpoise, had possibly lesser impact on fish because of low overlapping with their distribution (< 11 %). By the results of correlation analysis, capelin and polar cod were the priority potential prey for baleen whales (p < 0.01 and p = 0.02, respectively), whereas cod, haddock, blue whiting, and redfish – for toothed whales (p = 0.02, 0.01, 0.02, and < 0.01, respectively), in particular for white-beaked dolphin.

Data on feeding of fish are presented collected in the western Chukchi Sea aboard RV «Professor Levanidov» and in the eastern Chukchi Sea aboard RV «Ocean Starr» in August-September, 2019. The feeding was different by areas of the sea and reflected regional features of food base. Copepods and euphausiids were the main components of the diet, though their ratio varied. In the western Chukchi Sea, arctic cod and walleye pollock (40–70 cm) were the main consumers of food resources and consumed on average 3.85 and 8.38 t/km²  per day, respectively. The diet of walleye pollock included fish (4.05 t/km² . day) and zooplankton (3.01 t/km² . day, mostly euphausiids — 2.60 t/km² . day). Arctic cod consumed predominantly zooplankton (3.00 t/km² . day, mostly copepods — 1.27 t/km² . day, but also small- and medium-sized species). The total stock of net zooplankton (55.2 t/km² ) exceeded in 7 times daily consumption of zooplankton. Coelenterates, arrowworms, other plankton species, benthic species, and small-sized nekton were consumed by fish poorly. Daily food ration of arctic cod and walleye pollock was estimated as 7.4–9.4 % and 3.4–4.7 % of their body weight, respectively, so the food supply of these species in the western Chukchi Sea was quite sufficient in 2019. In the eastern Chukchi Sea, the diet of juveniles of walleye pollock, sand lance and arctic cod included mainly copepods (50.5 %), euphausiids (12.0 %) and oikopleura (17.0 %). Ratio of zooplankton stock to daily consumption was twice higher in the southern part of the eastern Chukchi Sea than in its northern part. The consumption was also higher in the southern area where the index of stomach fullness reached 114.8 ‱ for pollock juveniles and 262.0 ‱ for sand lance juveniles, whereas it was 87 ‱ for juvenile arctic cod and 47 ‱ for juvenile sand lance in the northern area. 

To compare trophic characteristics for pelagic and benthic communities of zooplankton and zoobenthos in the Chukchi Sea, isotopic composition of carbon and nitrogen (δ¹⁵N and δ¹³С) was measured in two different water masses: i) the Bering Sea water with relatively high δ¹³С and low δ¹⁵N values that occupied the southern part of the sea (south of 71^о N), and ii) the cold Arctic water prevailed in its northern part were δ¹³С value was considerably lower and δ¹⁵N value was higher in 1–3 %. Stable difference in the isotopic composition of carbon is found between zooplankton and benthic invertebrates in the southern Chukchi Sea that means that benthic organisms base mainly on the benthic trophic chain and role of organic matter from the upper layer is not significant. About 90 % of the studied species of benthic fish are locked into the benthic trophic web there. In the northern Chukchi Sea, the benthic community consumes mainly the suspended organic matter produced in the water column, with prevalence of ice algae. All samples of benthic fish collected in this area have minimum content of heavy carbon δ¹³С with the values comparable to pelagic fish that indicates the main role of pelagic objects (60–80 %) in their feeding. The δ¹⁵N value reflects predatory habits of the animals. These values vary over a wide range both in the southern and northern areas that corresponds to the diet of the first, second or third order consumers.

Biology, spatial distribution, migrations, and stock dynamics are considered for arctic cod in the Russian sector of the Chukchi Sea and adjacent waters of the northern Bering Sea on the data of trawl surveys conducted by Pacific Res. Inst. of Fisheries and Oceanography (TINRO) in 1971–2020, fishery statistics and cited data. Active fishery of arctic cod occurred in late 1960s — early 1970s and in 1980s, when annual catch of this species reached 24,500 t. Mean size of arctic cod in trawl catches increased southward with decreasing of the underyearlings portion; the mean size was larger in catches of bottom trawl than in catches of midwater trawl because of the same reason. The females became adult from the size 11–12 cm, the males — from the size 8–9 cm. Diet of arctic cod included benthos and plankton, as well as juvenile fish. Spawning of arctic cod in the Chukchi Sea in summer-autumn was never observed, but some fish ready to spawn were found in the Bering Strait in this season. Arctic cod aggregated in the coastal zone of the southern Chukchi Sea in August, then partially migrated to the Bering Sea through the Bering Strait in September-November. The portion of the Chukchi Sea stock involved into this migration depended on fall oceanographic conditions — it was considerably larger in cold years with early freezing of the sea. Back migration from the Bering Sea to Chukchi Sea depended on spring environments — only a part of the fish of Chukchi Sea origin returned back in cold years with late ice melting and the rest spawned in the Bering Sea, whereas almost all the fish returned to the Chukchi Sea for spawning in warm years with early melting. The stock of arctic cod in the western Chukchi Sea varied in 1971–2020 between 3.5–396.5 . 103  t, on average 80.6 . 103  t in the bottom layer, and between 4.0–329.2 . 103  t, on average 150.6 . 103  t in the upper layer.

Total content of arsenic in muscles and liver of the main commercial fish species landed in the Barents Sea, as atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, long rough dab (american plaice) Hippoglossoides platessoides, greenland halibut Reinhardtius hipoglossoides, and european plaice Pleuronectes platessa is considered on the data collected in 2009–2020. The average As content in the muscles of examined fish met hygienic standards for the permissible concentration, i.e. 5 μg/g of wet weight, but the content in liver was about twice higher. High variability of the total As content in muscles of juveniles and adult fish was observed that imposed excessive restrictions on their sales as food products. Taking into account that the increased content of arsenic in tissues of fish in the Barents Sea has natural origin, these restrictions are not directly related to actual quality of the fish raw materials. There is recommended to account the natural background of As and establish a regional criterion for the allowable concentration of total arsenic in the muscles of fish landed in the Barents Sea as 12 μg/g WW. For principal decision on the safe level of arsenic content in fish products, introduction of a new standard for the level of inorganic arsenic content is recommended, that is more reliable and representative indicator.

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.

Data of observations and published materials on linear and weight growth of pacific cod in the first year of life are analyzed for different habitats. The growth curve is approximated by logistic function. Monthly increments for the body length of larvae and fry are about 50 % in the first three months of life, when growth is the most intense. Absolute length increments increase in the first half of the year and reach the maximum of 25-30 mm per month in late summer — early autumn, then decrease in the rest of the year. Relative body length increments decrease in autumn and winter, too. The cod grow faster in southern areas. Weight growth patterns are different from the linear growth. The weight growth is the most intense in the first half of year, when relative weight increments exceed significantly the length increments — monthly weight increments decrease gradually form 142 % in the first month of life to 85 % in the sixth month. When the weight reaches app. 4 g, the relative weight increments decrease abruptly though the absolute increments continue to increase until the 7–9th months of life when they reach 8–10 g per month for fish with body length > 10 cm. The cod weight increases by 58 % in this short period of the highest growth. Time lag between the peaks of absolute increments of length (in the sixth month of life) and weight (in the eighth month) is about 2 months

Species composition of fish in the bottom biotopes of Peter the Great Bay (Japan Sea) is considered for 8 biostatistical areas on the data of 2428 trawl catches obtained in 36 surveys conducted by Pacific Res. Inst. of Fisheries and Oceanography (TINRO) in 1978–2009. The main 10 species for the depth ranges 20–50 m, 50–100 m and 100–200 m are ranked by biomass. Japanese flounder Pseudopleuronectes yokohamae had the 1st or 2nd rank at the depth < 50 m in all areas where it was 15.8–25.0 % of the total fish biomass, but was almost absent deeper, being a sublithoral species. Arabesque greenling Pleurogrammus azonus had the largest summary stock in the bay that was 6.8–30.6 % of the total fish biomass at the depths < 50 m, 8.1–34.3 % at 50–100 m, and 0.7–43.7 % at 100–200 m. Saffron cod Eleginus gracilis lived everywhere and had the 2nd–4th rank at the depths < 50 m (1.1–6.1 % of the total fish biomass), the 4th rank at 50–100 m (5.2–9.9 %), and 8th rank at 100–200 m (2.5–6.8 %). For the depths < 50 m, the densest distribution of fish was observed in the middle areas of the Amur Bay (25.0 % of japanese flounder and 26.0 % of saffron cod) and Ussuri Bay (30.6 % of arabesque greenling and 16.1 % of japanese flounder), on average. At the depths 50–100 m the highest distribution density was in the middle Ussuri Bay, too, where walleye pollock (14.4 %) and arabesque greenling (13.4 %) prevailed. At the depths 100–200 m, graypurple sculpin (32.1 %) and sea plaice (15.6 %) had the densest concentration in the Posyet Bay and arabesque greenling (43.7 %) and graypurple sculpin (9.0 %) — in the central part of Peter the Great Bay. Generally, mean biomass of fish was lower in the western Peter the Great Bay than in its eastern part that included such high-productive areas, as the Ussuri Bay and the central Peter the Great Bay.

Influence of the Siberian High longitudinal position on cyclonic activity over the Far Eastern Seas and the Pacific Ocean in winter, spring and summer is considered. Eastward shift of this atmospheric center causes general decreasing of number of cyclones over the region, but their intensity increases; on the contrary: cyclones are more frequent but weaker when the Siberian High is located in western position. The Siberian High, being a winter center, cannot influence directly on spring and summer cyclones, but it influences on formation of the Far Eastern Low, which intensity correlates with number and intensity of spring and summer cyclones.

High mortality of yesso scallop at the age of 0+–2+ is detected recently on aquaculture farms in Primorye (Japan Sea). Pathological changes and death of the mollusks are observed more and more frequently with increasing of their density and number of plantations. High values of damage and mortality of mollusks grown in cages are not caused by violation of the cultivation technology but by influence of pathogenic species. At the eastern coast of Primorye, high mortality of the scallop spat occurs because of their soft tissue detachment from the shells by alveolates of gen. Perkinsus (for instance, up to 78 % of scallops at the age of 5–6 months are damaged in the Moryak-Rybolov Bay). In Peter the Great Bay, 58–80 % of scallops at the age 2+ grown in cages have blackening, stratification and abnormal shape of shells, besides, all mollusks from the Voevoda Bight aged 2+ have large fouling (on average 8 % of their total weight). In the Nakhodka Bay, located between these areas, 60 % of the mollusks suffer both from soft tissue detachment and abnormal shape of their shells. In total, representatives of 14 groups of parasites are found in tissues and on shells of cultivated yesso scallop, including epibionts (macroalgae, sponges, ascidians, shellfish, bivalves and gastropods, polychaetes, barnacles) and pathogens (fungi, flagellates, ciliates, turbellaria, alveolates, bacteria). Some parasites are found on gills of scallops (ciliates Trichodina sp. for 22.2 % of mollusks, turbellaria for 37.1 %, flagellates for 100 %), whereas zoosporangia Perkinsus infect mantle, gills and muscle for 55.5 % of mollusks. However, the scallops collected from nature habitats in Peter the Great Bay, have no external signs of infection in the first year of life, the scallops at the age 1+ year have no lesions and changes of the shell shape, with minor exclusion, and only at the age 2+ their shells are damaged for 58–80 % of mollusks. The fouling of shell is not a direct cause of the scallops death, but contributes to their weakening and development of diseases. So far as external damages of shells are highly variable, mixed infection of cultivated mollusks can be assumed. 

Current state of functional nutrition is analyzed. Principles and methods for production of the natural and artificially enriched functional food of animal origin in Russia and other countries are overviewed. Possibility of using the fish reared at fish farms as a raw material for functional nutrition is shown. Experience of such raw materials production in aquaculture is still insufficient, in particular for the in vivo enrichment. High-quality raw materials for the functional nutrition can be produced in aquaculture with recirculated water system. Meat of rainbow trout (Oncorhynchus mikiss Walbaum) reared up to the weight of 380 g in a model recirculated water system contains on average 1.28 g omega-3 polyunsaturated fatty acids per 100 g, whereas its consumption rate is 1–3 g per day for human adults. Selenium content in the meat of the rainbow trout underyearlings fed during 110 days by the preparation Essex (1 mL/kg of feed) has increased up to 20.1 mg/100 g (7.3 mg above the control) that corresponds to 28.7 and 36.6 % of the daily consumption rate of selenium for man and woman, respectively. This raw material can be used for production of ecologically clean and functional food products in cases of selenium scarcity. Besides, survival rate of the underyearlings increased by 11.7 % and their yield by 17.5 %. Prospects are shown of a new direction in innovative biotechnology toward production of functional food in high-tech industrial aquaculture using a purposeful enrichment of fish meat with specified nutrients

Pure species obtained from the breeding stocks of the Pacific branch of VNIRO (Russian Res. Inst. of Fisheries and Oceanography), as kaluga Huso dauricus and amur sturgeon Acipenser schrenckii, as well as reciprocal hybrids between them K×AO and AO×K, were grown in parallel in tanks with recirculation aquaculture system (at fish farm near Moscow) and in net cages with heated water (at fish farm in Luchegorsk, not far from Vladivostok) for three years, 2018–2020. Survival, growth rate, feed costs, and cultivation density were determined for the experimental groups of fish on the main biological stages (embryos, larvae, fry, juveniles). Certain differences in survival and growth rate were found between the pure species and hybrids cultivated in different conditions. In the embryonic period, both survival and growth rate were higher for fish in cages, possibly because of long transportation of eggs to Moscow. For other stages, survival of K×AO was the highest in tanks, with exception of one-year-old fish, whereas survival of kaluga was the lowest at this farm, with exceptions of early juveniles (weight 2–3 g) and two-year-old fish. For Moscow farm, survival in tanks was: kaluga 9.3 %, cross K×AO 21.7 %, cross AO×K 26.8 %, amur sturgeon 28.9 %. For Luchegorsk farm, survival in cages was: kaluga 10.5 %, cross K×AO 11.5 %, amur sturgeon 19.5 %, cross AO×K 21.2 %. The effect of heterosis was observed for survival in cages, but not in tanks, where the rates for hybrids were between the rates for their parental species. At the third year of cultivation, the greatest weight increments were observed for kaluga and K×AO in cages and for kaluga and AO×K in tanks. By the autumn of the third year, the average weight in tanks exceeded this one in cages in 2.0 times for AO×K and amur sturgeon, in 2.5 times for kaluga, and in 3.0 times for K×AO. Kaluga and hybrid AO×K had the best growth rate in cages at Luchegorsk farm, but Kaluga and hybrid K×AO had the highest growth in tanks at Moscow farm. The integral score accounting the main indicators of fish breeding, as body weight of fingerlings, survival and feed cost, for the cage growing was the best for hybrid AO×K and for the tank growing — for hybrid K×AO. The comparative experiment confirms technological advantages of the sturgeons breeding in tanks. Due to warmer conditions of the growing, commercial product of kaluga and cross K×AO can be obtained by the middle of the second year of cultivation, and other species reach the commercial weight in the third year. In the case of cage breeding, kaluga and cross AO×K only reach the commercial weight in the third year of cultivation.

Linear growth and weight of bivalve mollusks cultivated in polyculture are considered. Cages with three mollusk species, as blue mussel, long-necked clam (mya), and macoma, were hanged at the depth of 1.0–1.5 m in the Tauiskaya Guba Bay, Okhotsk Sea. Several sets of these species with ratio mussel : mya : macoma 30 : 35 : 35, 50 : 25 : 25 and 70 : 15 : 15 were tested in the period from June 15 to October 26. The species ratio of 30 : 35 : 35 and 50 : 25 : 25 provided the highest linear increments for mussels (7.4 ± 0.3 and 7.1 ± 0.5 mm, respectively) and the highest weight increments for mya (7.8–8.2 g). The species ratio of 70 : 15 : 15 was the most favorable for weight growth of macoma (weight increments 1.6 ± 0.1 g). Mussels were distinguished by the largest elimination among all species in the polyculture — 7.5–8.8 %, whereas losses of macoma were the lowest — 1.9–2.1 %. The polyculture is considered as a prospective approach for bivalve mollusks cultivation in the northern Okhotsk Sea.

Australian red-claw crayfish Cherax quadricarinatus is a prospective species for aquaculture distinguished by high growth rate and good survival, in comparison with other cultivated crustaceans (shrimps, crabs). Results of experimental cultivation of this species under closed water supply with formation of the replacement broodstock are presented. The main stages of biotechnology are described. Size and weight properties of cultivated juveniles and indices of environmental quality are registered.