Scientific monitoring of pelagic fish stocks in 2004–2005 and 2014–2017 provided information on characteristics of sexual maturation of Atlantic chub mackerel Scomber colias in the coastal waters of the Central-Eastern Atlantic. Based on these results we describe ecological and geographical variability of some biological characteristics of the species. Features of sexual maturation of females and males of the mackerel can be described by a logistic equation obtained in the R programming environment. Fork length, at which 50

The material was the data of trawl-acoustic surveys and fishing nets in the reservoirs of the Tver region during resource research in 2007–2022, as well as archival data. As a result of the closure of the fishery by the State Committee of the Russian Federation for Fisheries in 2007, in order to preserve and more efficiently use the ichthyofauna of rivers, lakes, reservoirs, there was a decrease in commercial fish stocks in the reservoirs of the Tver region. Also, due to an increase in the concentration of some fish species (bream, bream), infection with ligulosis has increased. Periodic outbreaks of this disease have already been noted in reservoirs after the closure of the fishery, which will lead to a decrease in the efficiency of natural reproduction and further to a decrease in the number of fish. Due to the lack of fishing in the reservoirs of the Tver region, the possibility of catching almost 32,3 thousand tons of fish was lost for 15 years, which in monetary terms amounts to 5,15 billion rubles.

Genetic methods based on the study of the variability of mitochondrial (COI) and nuclear (microsatellites) DNA were used to study the processes of morphogenesis in the genus Eleginus. The revealed level of genetic difference characterizes the Pacific saffron cod (Eleginus gracilis) and navaga (Eleginus nawaga) as independent species that diverged in a relatively recent period at the boundary of the Pliocene and Pleistocene. The White Sea populations of navaga by microsatellite markers differed from the Navaga inhabiting the basins of the Kara and the Barents seas. At the same time, it is assumed that the Kara-Barents Sea region could have acted as a “glacial refugium,” which ensured the postglacial settlement of navaga, including in the “watered” White Sea depression. Phylogenetic analysis based on diversity of COI haplotypes reveals demand of possible reorganization in the order Gadiformes, including Eleginus in an independent subfamily—sister in relation to the subfamilies Gadinae, Lotinae, and Merlucciinae. The prospects of improving genetic methodological approaches in the framework of the development of research on Saffron cod are noted.

Kildin cod Gadus morhua kildinensis is a subspecies of Atlantic cod with extremely small population size, listed in the Red Data Book of the Russian Federation, which inhabits the waters of a small meromictic lake on the Kildin Island (Barents Sea). Comparative studies of morphobiological characteristics and feeding habits of Kildin cod in the juvenile period were conducted for the first time. Comparison of sample sets of adult Kildin cod and fingerlings on the basis of multivariate analysis of variance demonstrates a high degree of differences in the complex of morphometric characters. The diet of the analyzed sample set of Kildin cod fingerlings consisted of ostracodes (Ostracoda), larvae of polychaetas (Polychaeta), cladocerans (Cladocera), and gammarids (Gammaridae). The special features of changes in the diet of Kildin cod in the early ontogenesis are discussed.

The biological features of Atlantic cod in the coastal zones of the Murman for 1999–2006 were studied. The age composition, growth rate and maturation, feeding habits, and structure of otoliths were analyzed. Histological and genetic studies were carried out. It has been shown that young cod mainly lives and spawns in Western Murman bays. Older cod leaves the bays due to insufficient food supply. The growth rate of young coastal cod is comparable to that of cod in the open part of the Barents Sea. With age, the cod of the open sea areas noticeably overtakes the cod that lives in the coastal zone in growth. It was noted that the cod spawns in the bays with both coastal and Atlantic types of otoliths. Studies of genetic polymorphisms indicate a high degree of genetic similarity between cod groups in the Norwegian and Barents Seas under the influence of currents (branches of the Norwegian Atlantic Current, the Murmansk Coastal Current) and against the background of migrations at different stages of ontogeny of cod from coastal and open water areas.

We conduct a study of genetic diversity in groups of Atlantic mackerel from the waters of the Central East Atlantic on the basis of seven microsatellite loci. All loci are polymorphic, the estimates of expected heterozygosity vary from 0.021 to 0.914. A heterozygosity deficiency is identified for all studied samples of Atlantic mackerel, associated with the presence of null alleles in four of the seven studied microsatellite loci. A low but significant value of genetic differentiation is obtained, calculated for all loci (θ = 0.0052), which, presumably, may also be associated with the violation of panmixia due to the formation of individual subpopulations as a result of the uneven impact of fishing in different localities.

The distribution of the Kildin cod Gadus morhua kildinensis in Lake Mogilnoye (Kildin Island, Barents Sea) is assessed based on the results of echo sounding and hydrological surveys, underwater photography and field observations. Underyearlings live in the lower part of the freshened upper layer, younger age groups locate in vicinity of the natural dam in the southeastern part of the lake, adults are distributed along the water area of the lake within the depth range of 4.0–6.4 m (mainly 5.0–5.4 m), characterized by favorable temperature values, water salinity, and oxygen saturation.

— The hematological parameters of the peripheral blood of the Atlantic chub mackerel Scomber colias , bonito Sarda sarda, and splendid alfonsino Beryx splendens are presented based on materials of scientific monitoring on board the fishing vessels in the exclusive economic zones of Morocco and Mauritania in the years 2004–2017. A larger number of immature erythropoietic cells was recorded in the alfonsino, which is probably due to its possible vertical feeding migrations to greater depths with high pressure and low oxygen content. The analysis of erythropoiesis and the leukocyte formula revealed features of physiological and immunological aspects. Bonito has a higher monocyte content than atlantic chub mackerel and alfonsino, which indicates a high level of innate cellular immunity, represented by phagocytosis.

A comparative analysis of the biological and morphometric characteristics of the Pacific herring Clupea pallasii from different parts of the range, from the White Sea to the Yellow Sea, was performed. Forming of the modern species range, covering the waters of the Arctic, boreal, and subtropical zoogeographic zones, was preconditioned by the system of adaptations developed during the long evolution in the specific conditions of the northern Pacific Ocean. The results of multivariate discriminant analysis indicated relatively small differences in the complex of meristic features when comparing the samples from the Pacific Ocean and the samples obtained in the Arctic Ocean and the north-eastern Atlantic Ocean.

The first description of the histology of the digestive tract of the lumpfish Cyclopterus lumpus showed an adaptation for collecting and storing water. The morphology of this species' tract is mostly typical of carnivorous fishes, having a sac-like stomach for storage and a relatively short intestine of approximately 1.2× the standard body length. The esophagus is relatively short (0.13× standard body length) and thick-walled; it has a thick muscular coat, and its thickness changes from 0.4 to 1 mm during contraction. The stomach has well-developed gastric glands and is divided into the histologically distinguishable cardiac, fundus, and pyloric parts. The intestine has the same structure throughout its entire length. The water-holding ability of lumpfish is provided by well-developed muscles in the esophagus and stomach distensibility, which differs morphologically from the method used by Tetradontidae and Diodontidae species, who store water in the caudal part of the esophagus. The morphology of the digestive tract proved that this species is an intermediate between Tetradontidae and Diodontidae, which could inflate their bodies by swallowing certain amounts of water, and other fishes which are not able to do so. Results of the work extend current knowledge on the morphological capability of the digestive system of teleost fish, providing water-blowing behavior.

Using ten microsatellite loci, the analysis of genetic variability and differentiation of the Pacific herring Clupea pallasii over a wide geographic range in the Sea of Okhotsk, the Bering, Chukchi, Kara, Barents, and White seas was performed. A similar level of genetic variability is shown for the herring belonging to three geographical subspecies. The genetic structure at a large scale is most pronounced between the three geographical subspecies of herring, with the different level of genetic differentiation within each of the subspecies. Herring of the Pacific distribution range is differentiated only at the level of large basins, the Sea of Okhotsk and Bering Sea, which indicates a significant level of gene exchange, as in the southeastern part of the Barents Sea and in the Kara Sea. However, the gene flow in the White Sea herring is limited to a very small spatial scale.

Arctic rainbow smelt Osmerus dentex is one of the most abundant fish species widely distributed in the NW Pacific and Arctic seas. Studying this species can contribute to understanding the microevolutionary processes of the Arctic fauna in unstable climatic conditions and new habitats. However, little is known about the genetic structure and the mechanisms underlying its population dynamics. Ten microsatellite loci were used to genotype 822 individuals in 20 locations throughout a large part of the species' range in the Sea of Japan, Sea of Okhotsk, Bering, Kara, and White seas (across more than 11,000 km). O. dentex displayed substantial levels of genetic differentiation (overall F-ST = 0.067, R-ST = 0.091) and STRUCTURE identified eight distinct clusters. The significant regional variation was demonstrated in both genetic diversity and population structure, most notably between Arctic and Pacific basins. On a regional scale, contrasting patterns were revealed with limited gene flow between populations of the Arctic region (F-ST = 0.117) and high gene flow between the Bering Sea (F-ST = 0.017) or Sea of Okhotsk (F-ST = 0.031), which were probably associated with differences in larval distribution from the spawning grounds due to different oceanographic conditions of the studied areas. These results demonstrate the effect of local contemporary forces in shaping different patterns of genetic connectivity and diversity within O. dentex.

Pacific herring Clupea pallasii Val. — an important commercial species, the range of which covers not only the boreal waters of the Asian and American coasts of the Pacific Ocean, but also extends to the coastal waters of northern Eurasia. The article examines the features of the ecological, biological, morphological variability of the Pacific herring in the extended range from the White to the Yellow Seas, covering the waters of the Arctic, boreal, subtropical zones. The modern habitat of the Pacific herring is represented by two subunits: the ancient range (about 5 million years old) (the coastal area of the North Pacific) and the newly formed range (about 6 thousand years old) — (shelf zones of the Bering, Okhotsk, Yellow Seas, the Arctic coast of Eurasia). The highest growth rate is characteristic of herring in the boreal zone; the lowest values were found for herring from the Kara Sea and the White Sea spring-spawning herring. The results of multivariate discriminant analysis illustrate the similarity of Pacific herring in different areas of the range in terms of a set of meristic characters. The features of changes in the temporal characteristics of the spawning period in Pacific herring in different parts of the range are considered.

We performed a population genetic analysis of 22 Pacific cod sample sets (n = 986) based on the mtDNA control region (599 bp) polymorphism, which made it possible to specify four distinguished groups of this species: (1) within the seaward parts of the Bering Sea and Sea of Okhotsk and northern part of the Pacific Ocean, affected by the Pacific Ocean gyres; (2) coastal areas of the East/Japan Sea; (3) northern part of the Sea of Okhotsk, more similar to the second group from the East/Japan Sea by haplotype sets than to the seaward groups, despite limited reproductive contacts, special hydrological conditions, and the history of formation of the sea areas; (4) fundamentally different Pacific cod from the Yellow Sea adapted to the conditions of the shallow water area in the subtropical region.