Results of analyses of genetic diversity and phylogeography for polar cod Boreogadus saida in the Pacific Arctic are presented. Analyses leverage polymorphism of Cyt b and COI gene fragments obtained from samples in the Russian Arctic, as well as samples available in open databases. According to these markers, although polar cod demonstrates high haplotype diversity, our results suggest no clear population structure within the Russian Arctic, the Beaufort Sea, and the North Atlantic. This may be explained by the peculiarities of the life cycle of polar cod, particularly oceanographic mechanisms related to the mixing of pelagic eggs and the dispersal of early juveniles by currents and their movement following ice drift within the open waters of the studied area. Results are presented within the context and consideration of existing hypotheses of the origin of the common ancestor of Boreogadus, Arctogadus and Gadus, hypotheses of the divergence of these genera, the formation of the modern range of polar cod and the causes of the genetic diversity of its mitochondrial DNA. We also provide a reconstruction of the evolution of mitochondrial lineages of polar cod, according to one of the possible scenarios of its evolutionary history.

A new species, Ophthalmolycus auxilepis sp. nov., is described from ten specimens collected in the West Antarctic waters, Scotia to Weddell Sea, at a depth of 315–544 m. The new species is characterized by the extensive squamation fully covering the abdomen, predorsal area, and pectoral axil in adults; the presence of three nasal pores along with an absence of an interorbital pore; a double incomplete body lateral line; symmetrical vertebrae; and a characteristic coloration with white-margined dorsal and anal fins, and an extensive dark blotch on the pectoral fin. Ontogenetic changes of the diagnostically valuable characters are described. A revised key of species is provided. The possible Antarctic origin of the genus Ophthalmolycus is discussed.

Lycenchelys cyanosoma sp. nov. is described from a single specimen collected off the South Orkney Islands at 370-375 m depth. It can be easily distinguished from all known congeners by its lowest total vertebral count (76), dorsal- and anal-fin ray counts (71 and 54, respectively); unusual bluish coloration with blackish head; and the following additional features in combination: body fully scaled except the predorsal area but vertical fins completely scaleless; absence of oral valve, pseudobranchs and pyloric caeca; upper lip with pronounced flange; and periproct surrounded by peculiar tentacle-like processes. The new species is probably the smallest member of the genus, having developed testes at 98 mm standard length. Lycenchelys argentina, a rare and poorly-known species with a variable morphology, is herein redescribed based on a new (fourth known) specimen; we discuss the limits of its morphological variation. Lycenchelys cyanosoma sp. nov. and L. argentina may represent vicariant species with upper and lower bathyal/abyssal range, respectively. The diagnostically valuable features and known distribution of all Antarctic and Subantarctic Lycenchelys species are presented.

Using 209 polar cod Boreogadus saida individuals from the Russian Arctic and the eastern Chukchi Sea, as well as three Arctic cod Arctogadus glacialis individuals (5194 SNPs), we detected not only old gene introgression between the species' genomes in both directions but also discovered relatively recent hybrids. A total of 115 samples (3917 unlinked SNPs) demonstrated differentiation into two distinct genetic clusters: “Western” and “Eastern”. Samples from the Barents, Kara, and Laptev Seas were almost entirely represented by pure individuals of the “Western” cluster, while samples from the East Siberian and Chukchi Seas were represented predominantly by individuals of mixed origin, with a few pure individuals of the “Eastern” cluster. It was determined that loci differentiating individuals from the western and eastern seas of the study area are predominantly located on chromosomes 1, 2, and 3. After conducting a meta-analysis of all studies of polar cod population structure based on microsatellites and SNPs conducted to date, we can hypothesize the existence of five polar cod groups within the species' entire range. A total of 1868 loci with significant linkage disequilibrium allowed us to identify the presence of inversions on several polar cod chromosomes, unrelated to the geographic origin of the individuals. In particular, the most obvious differentiation into two groups of homozygotes and a group of heterozygotes for the inverted region is characteristic of chromosome 12 (based on 97 SNPs). The highest contribution to differentiation into three clusters among the SNPs of chromosome 12 was made by SNPs annotated to the netrin 1b gene. A stop codon was also discovered in the solute carrier family 4 member 5b gene on chromosome 18, which could hypothetically be associated with adaptation to different depths. Thus, the genetic diversity of polar cod represents a complex array of linked and unlinked loci that may explain ecological adaptation of this species to the diverse environmental conditions of the Arctic Ocean and the vast extent of its range.

The results of extensive research over four decades (1983-2024) investigating the spatial and depth distributions, catch per unit effort (CPUE) dynamics, and basic biological characteristics of the understudied mud skate Bathyraja taranetzi throughout its range are presented for the first time. Data used in this study were collected from Russian bottom trawl surveys and supplemented by publicly available databases. Regions with the densest aggregations of mud skate were identified in the waters along the eastern slope of the Bering Sea, off the Aleutian Islands, and in Pacific waters off southeastern Kamchatka and the northern Kuril Islands. The species was most abundant in these areas at depths between 201 and 400 m. Individual total length (TL) ranged from 11.3 to 74 cm, with the majority between 46 and 65 cm. The average TL of females was 1.8 cm larger and the average body weight was 0.17 kg greater than that of males. In the timeframe of these data, a considerable increase in the catch rate of mud skates was observed in most parts of their range. In Russian waters, CPUE initially decreased from 1985 until the early 2000s and then began to increase, while in US waters CPUE increased until 2010, after which catches began to decline.

The article presents comparative analysis of otolith characteristics (shape, size, and chemical composition), growth rates, and age for four species of the sculpin genus Batrachocottus (Cottidae) inhabiting the full depth gradient of the world’s deepest lake, Lake Baikal. Our findings demonstrate that within the tested group of species, otolith shape becomes simpler, growth rates decrease, and lifespan extends accordingly with habitat depth. Such trends were previously documented only in certain marine fish taxa. Their presence in the evolutionarily young Baikal Cottidae suggests that such traits arise in fish colonizing deep-water environments, regardless of taxonomic affiliation or evolutionary history. Significant differences in otolith chemical composition were observed among species of the genus. These findings underscore utility of otolith analysis in studying deep-water fish ecology and provide evidence for convergent evolution in fish adapting to deep-water habitats.

Studying fish winter ecology in seasonally frozen water bodies is hindered by the difficulty of deploying fishing gear under ice. Traditionally, gillnets have been set using long poles to guide the ropes needed for further net setting. This paper presents two experimental techniques for deploying nets under ice: using a self-propelled torpedo (Vitfishing) and a new method developed by the authors that utilizes flexible fiberglass poles. The effectiveness of these methods was evaluated through field experiments in two model morphologically distinct lakes, Lakes Baikal and Goltsovoe (Transbaikalia), where the catch per unit effort (CPUE) of the nets was compared. Statistical analysis showed no significant difference in catch efficiency between the two methods. Therefore, the choice of method should be based on practical convenience in specific field conditions.

The relationships between the distribution and quantity (biomass and abundance) of the ten most abundant fish species and environmental factors (physical and chemical) in the lower mesopelagial (500–1000 m) of the Sea of Okhotsk were analyzed for the first time. These species included Stenobrachius leucopsarus, S. nannochir (Myctophidae), Leuroglossus schmidti, Bathylagus pacificus, Lipolagus okhotensis, Pseudobathylagus milleri (Bathylagidae), Bothrocarina microcephala (Zoarcidae), Coryphaenoides cinereus, C. pectoralis (Macrouridae), and Chauliodus macouni (Stomiidae). The physical parameters measured at 500 m depth included water temperature, salinity, dissolved oxygen, and chlorophyll a, whereas the chemical parameters analyzed were phosphates, organic phosphorus, nitrates, ammonia, organic nitrogen, and silicates. Relationships between mesopelagic fishes and environmental factors were evaluated via modern statistical approaches, including the CCA, PERMANOVA, and NMDS analyses. The results of the present study revealed statistically significant relationships between the quantity (biomass/abundance) of fishes and salinity, oxygen, and chlorophyll a. However, the main environmental determinants of the distribution and biomass/abundance of mesopelagic fishes in the study area remain poorly understood. Future research should focus on analyses of the relationships of mesopelagic fish with mesoscale oceanographic formations (e.g., frontal zones, upwellings, gyres, and eddies), distributions of forage resources, associated macroplankton, and predators.

Coelorinchus gilberti is a member of the grenadier family (Macrouridae) found off the Pacific coast of Japan (from Shikoku Island to Hokkaido Island), the Kyushu-Palau submarine ridge, and the Emperor Seamounts. This species is a common bycatch in the longline fishery for the skilfish Erilepis zonifer (Anoplopomatidae) and some rockfishes (Sebastidae). However, there is no published information on its distribution and biology. Based on observations on commercial longlines between 2014 and 2018, the catch distribution, size and sex, size of otoliths, age and growth, sex ratio and sexual maturity of C. gilberti in the waters of the Emperor Seamounts (NW Pacific) are presented. This species has been caught from Nintoku Seamount in the north to Kammu Seamount in the south and is most commonly found off the Jingu, Ojin, and Kammu seamounts. The species has been recorded from 215 to 1840 m, which significantly extends its known bathymetric range. The catches included individuals from 34 to 93 cm (mean 53.2 cm), weight 140-5240 g (mean 688.2 g) and age from 24 to 48 years (mean 37.9 years). The females were significantly longer, heavier and older than the males and generally dominated the catches (the proportion of males <40%). The growth of C. gilberti is best described by a von Bertalanffy growth function (VBGF), and the parameters of the von Bertalanffy growth equation were L infinity = 61.6, k = 0.09, t(0) = -1.4. Spawning individuals were recorded in catches only in April, which is the end of spawning. Further research with year-round trawl samples is needed to obtain more detailed information on the life cycle of C. gilberti.

The official data on Russian catch of sharks, rays and skates in the Pacific region over the last 45 years are analyzed. For Russian fishermen these fish have not commercial value, so when they are incidentally caught, they are not usually retained and not landed but discarded at sea. The total amount and annual dynamics of such bycatches, their distribution by water area, depth, fishing gear and types of fisheries are clarified. The fact that cartilaginous fish are not target fisheries in Russia has a downside. Incompleteness of bycatch accounting and species identification are the reasons that we can operate only with approximate total catches of all sharks and all skates. As a consequence, the low official Russian current total allowable catch of these fishes is estimated formally and remains at the same level for many years. Chimaera catch is generally unknown since in daily vessel reports they are listed as "other fishes". It is shown how to improve national data collection and analysis for elasmobranch monitoring, conservation and possible future sustainable fisheries.

The bigeye sculpin Triglops nybelini (Cottidae) is a widespread and abundant species in the Arctic and the adjacent North Atlantic playing an important ecological role in marine ecosystems. Consuming pelagic and benthic invertebrates and being prey for predatory fish and marine mammals, this species participates in the transfer of energy and organic matter between the lower and upper trophic levels. As a key part of a food web, bigeye sculpin indirectly supports some commercially important fishery resources. In addition, this species is a competitor for the food with polar cod Boreogadus saida and some other sculpins. Meanwhile, the data on its ecology and biology in the Arctic seas remain poorly understood, while there is almost no such data for the Laptev Sea (Siberian Arctic). Habitat characteristics and biological features of the Laptev Sea bigeye sculpin are presented for the first time. This species has been observed throughout the lower shelf and upper continental slope within the entire studied depth range of 110-752 m at bottom temperatures ranging from -1.30 to + 1.38 degrees C. The relative abundance (density) was within 21-653 inds./km2. Although dense concentrations of this species have not been observed anywhere, its maximum catches have been recorded within the 550-750 m depth range, which is somewhat deeper than published data on the optimal depths. Individuals aged 3-5 years with a total length of 66-110 mm and a body weight of 2-8 g dominated the studied samples. This species in the Laptev Sea is characterized by the presence of sexual dimorphism in the external morphological characteristics and sizes of mature males and females. Among the fish longer than 95 mm, the proportion of females increased sharply, reaching 100 %, with a total length > 100 mm. Despite the relatively diverse diet composition, the bulk of the diet (89 %) of the bigeye sculpin in the Laptev Sea was composed only of hyperiids and euphausiids concentrated within the near-bottom layer. As the size of this species increases, benthic organisms almost completely disappeared from its diet, and only hyperiids and euphausiids became the main prey. This may suggest that unlike many other sculpins, T. nybelini is a benthopelagic fish.

The results of the trawl survey of the research vessel Professor Kaganovsky over four seamounts (Annei, Jingu, Ojin, and Koko) of the Emperor Seamount Chain in 2019 are presented. Seventy-three species of pelagic and bottom-dwelling cartilaginous and bony fishes from 40 families were collected. Morphological diagnoses are presented for each species, with taxonomic comments for the poorly known taxa. The obtained collection includes 11 species new to science or of uncertain taxonomic position, 9 species newly reported for the Emperor Seamounts, and one new record Linophryne arborifera for the Pacific Ocean. For individual seamounts, 27 fish species were recorded for the first time at Annei, 12 species at Ojin, 4 species at Koko, and 2 species at Jingu Seamounts. Cytochrome c oxidase subunit I (COI) or cytochrome b (Cyt b) sequences were obtained for 36 species belonging to 22 families, including 13 species for which the barcode was flagged for the first time and the sequences made available. Cryptic diversity was revealed within the genera Cyclothone, Argyropelecus, and Chauliodus. According to our data, a boundary between the boreal and subtropical fish communities was found between Nintoku and Jingu Seamounts, with a transitional zone over Jingu and Ojin Seamounts at 37–39° N. However, the distribution of the subtropical species to the north may be limited by the increasing of summit depths in the northern subsection of the chain rather than any oceanographic or climatic barriers.

Large pelagic predatory fishes play an important role in marine ecosystems, occupying the highest position in food webs and accumulating energy and organic matter produced by aquatic organisms of lower trophic levels. Among pelagic predatory fishes, more attention has been given to the sharks, tunas and billfishes inhabiting equatorial and tropical waters, whereas pelagic predatory fishes inhabiting subarctic and temperate waters have been much less studied. We analyzed long-term midwater trawl survey data to investigate changes in the spatial distribution, ranges, and catch rates of the three most abundant large predatory teleosts in the Russian and adjacent waters of the northwestern Pacific, namely, the North Pacific daggertooth Anotopterus nikparini, the longnose lancetfish Alepisaurus ferox, and the Pacific pomfret Brama japonica. The northernmost distributions of daggertooth, lancetfish, and pomfret were observed in summer, spring, and autumn, respectively. All three species were characterized by the greatest northwards occurrence in the 2000s. In the study area, their maximum frequency of occurrence was recorded during the summer, and they were most frequently caught in the 1980s (lancetfish and pomfret) and 1990s (daggertooth). The average catch rates of daggertooth and pomfret were highest in summer, whereas those of lancetfish were highest in winter. The highest average catch rates of daggertooth, lancetfish, and pomfret were recorded in the 2000s, 1990s, and 1980s, respectively. The maximum absolute catch rates of lancetfish were recorded in winter, whereas those of daggertooth and pomfret were recorded in spring and summer, respectively. The maximum absolute catch rates of daggertooth and pomfret were observed in the 1980s, whereas those of lancetfish were observed in the 1990s.

The Alaskan (highbrow) sculpin, Triglops metopias, is a rare and poorly known species with a restricted distribution in the North Pacific. This species has been previously recorded only from off the Aleutian Islands and the Gulf of Alaska, while previous records from the western North Pacific have been controversial. The presence of T. metopias in the northwestern Pacific off the Kuril Islands is confirmed in the current study. Forty-one specimens were included in morphological and molecular analyses, including principal component analysis and DNA barcoding. The detailed morphological description of the Kuril Islands specimens is given. Molecular analysis inferred from the mitochondrial cytochrome b sequences showed no separation of this species from T. pingelii, although they can be distinguished by external morphology, including the use of the multivariate statistical approach. The geographical distribution of T. metopias in the North Pacific is discussed. This species is considered to be a recently diverged species with a disjunct distribution from the Kuril and the Aleutian Islands eastwards to the Gulf of Alaska. Despite its morphological similarity to T. pingelii, both species can be distinguished by a combination of meristic and morphometric characters, in particular, the wider interorbital space (10.4–22.4, mean 14.8 vs. 6.9–11.4, mean 9.2), shorter pectoral fins (18.7–24.9, mean 21.0 vs. 21.7–27.4, mean 24.1), and the on average more numerous oblique dermal folds (92 vs. 54).

Gnathophis johnsoni sp. nov. is described on the basis of 15 specimens (138–380 mm TL) from the Emperor–Hawaiian Seamount Chain in the western and central North Pacific. The new species is most similar in morphology to G. bathytopos (Atlantic), G. cinctus (eastern Pacific), and G. smithi (Nazca and Salas-y-Gomez Seamounts in the southeastern Pacific) by the sensory pore configuration and vertebral count, but differs from these species in the following characters in combination: darkly pigmented pectoral fin, dorsal fin with black margin broadened caudally and extended onto the distal half of the caudal fin, relatively long head, jaws, gill slit and caudal fin, and on average a greater preanal distance. Although most of morphometrics overlap between the new species and its closest relatives, multivariate statistical analyses clearly discriminate this species. Molecular analysis shows sister relationships between the new species and G. cinctus, with 1.81% of genetic divergence, which significantly exceeds the differences between the haplotypes belonging to the same species (0.36 and 1.08% of divergence, usually not exceeding 0.9%) and confirms both species as close but distinct. The close relationship of G. johnsoni sp. nov. and G. cinctus represents a rare case of biogeographical relations between western and eastern Pacific demersal fish faunas. Molecular data suggest that some morphologically similar species may represent independently evolved lineages, though the group of Gnathophis possessing elevated lateral-line pores is likely monophyletic.

Ophthalmolycus lacrimegalos sp. nov. is described from a single specimen collected off the South Orkney Islands, Weddell Sea, Southern Ocean at a depth of 1,495 m. The new species differs from its congeners by the combination of extensive squamation covering the abdomen, predorsal area, and pectoral axil; an enlarged lachrymal bone, a wide bony interorbital space, and other characters (cephalic pore configuration, meristics, body proportions, coloration, etc.) in combination. This is the sixth species of the genus in the Antarctic waters, bringing the total number of known species in the genus to ten. However, the distinction of Ophthalmolycus in its current composition from the species-rich genus Lycenchelys requires elucidation. A revised key to the species of Ophthalmolycus is provided.

The cartilaginous fishes (sharks, rays, and chimaeras) are one of the oldest groups of lower vertebrates, which in recent decades have been subjected to severe negative human impacts (overfishing, habitat destruction, pollution, etc.). Many shark species are caught in virtually unregulated and uncontrolled fisheries and processed into food and other products. The Pacific spadenose shark Scoliodon macrorhynchos is subject to intensive fishing in most of species’ range. At the same time, its abundance in Chinese waters is declining, while stocks around island of Taiwan (Chinese Taipei) and off the coast of Sarawak (Borneo, Malaysia) show signs of overfishing. This species, along with other members of the Carcharhinidae family, is listed in Appendix II of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) and NT (Near Threatened) on the IUCN (International Union for Conservation of Nature) Red List of Threatened Species. Recently, a new pet product, dried eviscerated specimens of S. macrorhynchos, supplied from China, has appeared in some Russian online shops. An examination of the dried sharks purchased from the online shop revealed that they were all immature specimens, exacerbating the already threatened state of the species' populations. Eliminating further threats to S. macrorhynchos will require a ban on fishing for undersized specimens, improvement of the national fisheries management, monitoring of population status, and increased control of international trade by CITES.

A large series of otoliths of 16 mesopelagic teleost fish species from the Irminger Sea, North Atlantic Ocean, are described morphologically to investigate the ontogenetic and intraspecific variation. The results show that the surface morphology of the otoliths between young and adult specimens is variable, especially in the alepocephaliform (Normichthys operosus, Sagamichthys schnakenbecki, Xenodermichthys copei) and astronesthine (Borostomias antarcticus) species. The diagnostic features of the otoliths can be used to confirm the identity of the species, especially in myctophids, where confusion between Benthosema glaciale and Myctophum punctatum may be possible. A SEM-based iconography of the otoliths of all studied species is presented.

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

Numerous studies show that species identification of representatives of the genus Alosa using various genetic markers is often difficult and the search for more specific biomarkers is required. For the first time we analyzed polymorphism of COI gene fragment of mitochondrial DNA of two representatives of this genus (A. tanaica and A. kessleri), supplemented with new data on A. immaculata, from the waters of the Ponto-Caspian basin in comparative aspect with other representatives of the herring (Clupeoidea) genera Alosa, Clupea, Clupeonella, Sprattus, and Sardinops. The main result was the conclusion that within the genus Alosa, it is not possible to identify species using the marker used. On the one hand, specimens collected from morphologically distinct individuals and identified as different species have the same haplotypes. On the other hand, samples belonging to different species differ from each other by an insignificant number of nucleotide substitutions and do not form independent clades on the phylogram and haplotype network. This indicates the absence of genetic differentiation between the studied samples of herrings of genus Alosa into separate species and species groups when using DNA barcoding based on the COI gene. The reasons for such a phenomenon may be the following: (1) incorrect identification of species in catches, since shads (Alosidae) have high morphological flexibility and in many species, the main external morphological characters often overlap; (2) recent time of speciation by the standards of biological evolution for shads of genus Alosa; (3) difference in proportion of interspecific hybrids, which can vary significantly between populations of the same species.