An Erratum to this paper has been published: https://doi.org/10.1134/S1063074025010018

The poacher Podothecus hamlini Jordan and Gilbert in Jordan and Evermann 1898 is redescribed on the basis of 35 specimens collected in northern Japan and southern Okhotsk Seas. This species can be distinguished from Podothecus veternus Jordan and Starks 1895 by the following combination of characters: 2–2.5 rows of dorsolateral plates between the depressed tip of first dorsal fin and the origin of second dorsal fin (almost no space in the latter); plates on caudal peduncle with conspicuous spines (no spine); no black bands on the body behind the head (present); and a black spot present between the 1st and 3rd spines of first dorsal fin (absent). It is suggested that there is no P. veternus in the Japan Sea and that all previous reports of this species are erroneous and refer to P. hamlini.

Two published mitogenomes of eelpouts, Lycodes raridens (GenBank accession no. MN604279 and RefSeq accession no. NC_053740) and L. ygreknotatus (GenBank accession no. LC093396), were found in an unexpected phylogenetic position clustering with distant zoarcid species outside the genus Lycodes. An analysis of single-marker sequences has confirmed that the observed phylogenetic inconsistencies result from incorrect species identification. The accession nos. MN604279 and NC_053740 represent actually the mitogenome of Ophthalmolycus amberensis mistaken for L. raridens, and the accession no. LC093396 represents the mitogenome of Zoarces gillii mistaken for L. ygreknotatus. Both misidentified mitogenomes were already reused in phylogenetic analyses and cited in multiple subsequent publications. Consequently, the present study has been undertaken with the purpose to prevent the propagation of wrong biological information that further confuses the phylogeny of the most problematic groups of zoarcid fishes.

The Derzhavin's sculpin (Radulinopsis derzhavini Soldatov et Lindberg, 1930) is a psychrolutids species that leads a cryptic life in coastal waters of the Japan Sea and the southern Okhotsk Sea. To date, larvae of this species have remained unknown; therefore, their biology is poorly understood. In the present study, the early developmental stages of R. derzhavini are described for the first time. In Peter the Great Bay, Japan Sea, this species is characterized by a spring spawning season (May) and a short pelagic period of larval development, usually from mid-May to the last 10 days of June. Species identification of the described larvae was confirmed by incubation, rearing of larvae in captivity, and genotyping of a fragment of the mitochondrial cytochrome c oxidase I (COI) gene. In addition, the development of pigmentation in larvae of this and related species was compared. Morphological analysis of both adults and larvae, together with complementary molecular genetics, confirms the previously obtained conclusions that the species of the genera Radulinopsis, Radulinus, Asemichthys, and Astrocottus form a natural group with monophyly by all types of data.

The first data on the distribution, habitat conditions, size composition and feeding of Lycodes brunneofasciatus (Zoarcidae) in the Sea of Okhotsk waters off the coast of Kamchatka are presented. High values of the distribution density of the species were recorded on the eastern slope of the TINRO depression and in the area north of the First Kuril Strait. The depth of catches of eelpout varied from 120 to 436 m, its highest relative abundance is typical for 200–300 and 401–436 m. In the study area, L. brunneofasciatus is predominantly an inhabitant of the Okhotsk intermediate water mass where it is found at a water temperature at the bottom of 0–1.8°C. This species is represented in catches by individuals with a total length of 32–72 cm. Bivalvia, Amphipoda, Gastropoda and Polychaeta prevailed in the diet of tawnystripe eelpout. In addition, Echiura was found in the stomach of one of the studied specimens with a length of 69 cm.

For the first time, we report the finding of egg masses and an egg-guarding male of the whip sculpin Gymnocanthus intermedius (Temminck et Schlegel, 1843) in Peter the Great Bay (Sea of Japan). Bottom eggs were found in the post-wintering period during a scuba dive at a depth of 12 m. Exact data on the depth of occurrence and structure of the egg masses, the number of eggs per mass, and the sex of the guarding parent fish are provided. The characteristics of the eggs and the substrate on which the egg masses were laid are described. The diagnostic features of the male that allowed it to be assigned to G. intermedius are given.

— The rare species Icelinus pietschi Yabe, Soma et Amaoka, 2001 was first discovered in the Russian waters in the Sea of Japan (the Peter the Great Bay). The characters and description of the analyzed specimen are reported. The species I. pietschi inhabiting the Sea of Japan may be supposedly found from the Peter the Great Bay to the water region off the south coastline of the Sakhalin Island and along the continental coastline northward to the Vladimir Bay and southward to the northern part of the Korean Peninsula.

A new species, Lycodapus imperatorius, is described from the seamounts of the Emperor Ridge, North Pacific Ocean. The new species can be identified by its stout gill rakers, single interorbital pore, four preopercular and four mandibular pores, 95–99 vertebrae, numerous vomerine and palatine teeth, and COI mtDNA sequences. Although the new species is most similar to L. endemoscotus and L. antarcticus in morphology, the closest match to already published sequences was Lycodapus fierasfer, which is fairly different from the new species in terms of morphology. The incongruence between molecular and morphological inferences might be explained by the homoplastic nature of the morphological characteristics used for species delimitation in Lycodapus. The percent of genetic identity between the closest species of Lycodapus ranges from 95.4 to 98.6% in comparison with 99.5–100.0% between individuals of the same valid species. A key of the genus is amended to include the new species.

The species composition of sculpins of the genus Malacocottus in the Sea of Japan is discussed. It is shown that only Malacocottus gibber Sakamoto, 1930 inhabits this sea. The name M. microphthalmus Popov, 1933 is a junior synonym of M. gibber. A new Russian name for M. gibber is proposed: yaponomorskii myagkii bychok.

Stichaeus ochriamkini (Stichaeidae) is common in the northern Japan Sea and the southern Okhotsk Sea. Among the five known representatives of the genus Stichaeus, early ontogenesis is the least studied in S. ochriamkini. In this study, the authors provide the first description of all larval stages of this species. In the north-western Japan Sea, larvae are found in plankton from early April to early June. S. ochriamkini larvae can be identified using the following characters: postanal-lateral pigment (PLP) lines present on the sides of the caudal part of the body and run along the anterior edge of hypaxial myomeres; 14-15 abdominal vertebrae; 32-34 rays in the anal fin; larvae disappear from plankton at a body length of L-T > 25.0 mm (L-S > 20 mm). Larvae of S. ochriamkini are very similar to larvae of Stichaeus punctatus. The melanin pigmentation in larvae of both species shows similar patterns of development. In the genus Stichaeus Reinhardt, 1836, two groups of species are distinguished by the presence/absence of PLP lines in larvae, and by significant divergence (clearly exceeding the species level) in the COI mtDNA gene. It is suggested the differences between these species groups is recognized at the generic level. Thus, the genus Stichaeus Reinhardt, 1836 should include S. punctatus and S. ochriamkini, whereas the other three species should be placed in the genus Dinogunellus Herzenstein, 1890: Dinogunellus fuscus, Dinogunellus nozawae and Dinogunellus grigorjewi.

A spawning ground of the Mud Skate Bathyraja taranetzi and the Okhotsk Skate B. violacea was recorded for the first time from Pacific waters off the northern Kuril Islands. It was located at 50°25′7″ N, 157°22′7″ E, and a depth of 350–351 m; the water temperature was 3.8°C. At the spawning ground, egg cases and recently hatched juveniles were found in large numbers.

— In the summer period of 2017, the threaded sculpin Gymnocanthus pistilliger occurred at depths from 14 (minimum depth of trawling) to 64 m in the Sea of Okhotsk off the western coast of Kamchatka. Areas of the maximum G. pistilliger concentrations are only partially similar in terms of fish mass and abundance. The maximum average catches in terms of biomass were recoded between 55° and 56° N, where a high abundance of the species was also recorded. The maximum average catches in terms of abundance were obtained southerly, between 53° and 54° N. The species is the most common and abundant to the depths of 40−50 m. The length of specimens varies within 6−26 (on average 18.3) cm. The ratio of males to females is 0.4 : 1. The smallest sizes of specimens of both sexes were recorded in the depth range of 14−20 m; the average sizes of males and females increase with depth. In the summer period, G. pistilliger occurs in a wide temperature range between 0.4 and 12.1°С on the West Kamchatka shelf. The highest catches of the species were recorded at the temperature of 1.0−3.5°С in the main part of the bathymetric interval, and at 3.5−6.0°С in a shallow zone. According to the results of summer surveys off the western coast of Kamchatka the estimated abundance of G. pistilliger was 146 million ind., and the biomass was 11200 t.

Data on the first records of Pholis nea Peden et Hughes, 1984 from Russian waters of the Sea of Japan (Tatar Strait) and a description of the species morphology are presented. The genetic identification is based on an analysis of the COI gene region of mitochondrial DNA (mtDNA). A new common English name is here proposed for Pholis nea, the Lesser Gunnel.

The larval development of Chirolophis japonicus and Ch. saitone from the yolk-sac stage to the settlement on the bottom is described from waters of Peter the Great Bay, Sea of Japan. The pattern of distribution of melanin pigmentation over the body of larvae in these Chirolophis species is formalized for the first time. It consists of six rows, the aggregation on the top of head, and several single melanophores. Despite the similarity between the species, each of them has its specific features that are manifested mainly as a different number of axial skeleton elements (total number of vertebrae and number of rays in the dorsal and anal fins). A conclusion is made that a reliable diagnostic character to identify larvae of Ch. japonicus and Ch. saitone within the period of their development from hatching to settlement can be the number of melanophores at the base of the anal fin rays.