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.

Experiments were carried out on intravital otolith-tagging of juveniles of the ocellated blenny after transition to benthic life mode with Alizarin Red S. Marking at a dye concentration of 200 mg/L for 16–18 h at night, gave 100% formation of fluorescent marks with zero mortality of experimental individuals. Alizarin marks on the otoliths correspond to “stress” marks in the form of darker micro-increments, visible in transmitted light. The calculation of microincrements in the zone between two consecutive markings with an interval of 9 days confirmed the daily periodicity of their laying at this stage of development of the ocellated blenny. This allowed us to determine the period of hatching in natural conditions of juveniles in the Zhitkov Bay (Russky Island, the Peter the Great Bay, Japan sea). Hatching of larvae in 2017 in this species occurred, according to our estimates, from the last decade of March to the end of the second decade of April, with a peak in the first decade of April. Hatching begins even under the ice at a slightly negative water temperature of –1–0°C, but it proceeds mainly already at a temperature of 1–3°C, after the removal of ice from the bay. Taking into account the known timing of spawning of the ocellated blenny in the Peter the Great Bay (November–early December), we can state that the development of its eggs in this area is greatly slowed down at water temperatures below zero in December–March and can go on for 4–5 months, which is almost 3 times longer than the development time in more mild conditions of the south Hokkaido.

The Elegant sculpin Bero elegans is a plentiful but little-studied fish species that lives in the coastal shallow waters of the north-western part of the Japan Sea. In the study reported here, we assessed for the first time the life span, growth pattern, and age at maturity of this fish, based on growth and maturation observations and an analysis of the structure of otoliths from fish captured in Paris and Zhitkov bays, Russky Island, Peter the Great Bay, Sea of Japan in the period 2018–2022. The life span is estimated to be 47 months for females and 40 months for males. Males generally grow faster than females, but groups of slow-growing and fast-growing males that form during maturation are found. Both males and females spawn for the first time at 2 years of age. The von Bertalanffy’s growth function with three constants was used to calculate growth ( L t = estimated length as a function of time t [months]; L ∞ = theoretical asymptotic length; t 0 = theoretical time at 0 length; k = constant of linear growth), with the following values obtained: L ∞ = 176.294, k = 0.033436, t 0 = − 2.3394 at R = 0.95 for males; L ∞ = 118.389, k = 0.0536, t 0 = − 2.3464 at R = 0.94 for females (where R is otolith radius).

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.

The results of the study on the age structure of the population of the mud skate Bathyraja taranetzi from the Pacific waters off the northern Kuril Islands are presented. The modified method of staining the preparations of mud skate vertebrae with Harris hematoxylin, which significantly improves the distinctness of annual growth increments compared to the previously used ones, has been tested. Approximation models are proposed that make it possible to identify the true annual growth increments on the vertebrae, and consider the relationships between the radius of rings and age, body length and age, body weight and age at the time of formation of the annual increments. According to our data, the age of maturation of individuals of the mud skate turned out to be higher than that known for the population in the eastern part of the Bering Sea and also estimated with vertebrae, and significantly exceeded the results of age determination with caudal thorns obtained for the western part of this species range. It turned out to be about the same for males and females, 12–14 years. The estimated lifespan of individuals of this species was also significantly higher than previously believed.

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.

The ichthyoplankton of the upper epipelagic zone (0–50 m) was studied in the northern part of the Sea of ​​Japan in July–August 2017. Eggs of seven fish species and larvae of five fish species from five families were recorded off the coast of Primorye; eggs of six species from five families and larvae of 12 species from seven families, in the Strait of Tartary. Eggs and larvae of four species of the Pleuronectidae family ( Limanda punctatissima, Glyptocephalus stelleri, Cleisthenes herzensteini, and Acanthopsetta nadeshnyi ) prevailed everywhere. Off the coast of Primorye, Cl. herzensteini dominated, and in the Strait of Tartary, L. punctatissima . In comparison with the results of the Kuril-Sakhalin expedition performed the late 1940s, the eggs of pelagic fish species, such as Engraulis japonicus, Cololabis saira, and Scomber japonicus , was found in small quantities and only in the surface water layer. The results allow us to report on slight changes in the species composition relative to the middle of the last century, on the one hand, and significant changes in the dominant species, on the other.

The authors declare that they have no conflict of interest. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Larvae of Stichaeus fuscus from the Sea of Japan and the Sea of Okhotsk have been identified and their diagnostic traits described. Larvae of this species were collected in August to early October at a water temperature of 9.9–19.0°C and a salinity of 31.4–33.6‰. The size of larvae varies from 3.5 to 10.0 mm. The areas of finds of S. fuscus larvae fit the known range of this species well.

The features are discussed of the growth of threaded sculpin Gymnocanthus pistilliger in the southern part of its range, in the Sea of Japan. Several methods were tested to determine the age of this species. The improved approach is suggested for determinating the age of threaded sculpin by annual increments on sagitta using thin cross-sections, characteristics of optical density in different zones of otolith growth, and their positions relative to otolith center. It was demonstrated that the growth rate of threaded sculpin in the waters of southern Primorye was significantly higher than in the northern part of its range: the males reached a length of about 20 cm and the females about 22 cm at the age 5+. The maximum length of individuals, 26 cm in the males and 31 cm in the females, significantly exceed those known from literature. The longevity of threaded sculpin calculated for maximum size is 12–13 yr for the waters of Primorye.

The effect of zinc on the prelarvae of the Japanese anchovy Engraulis japonicus and on the sand flounder Limanda punctatissima punctatissima and of lead on the prelarvae of the Japanese anchovy was investigated. The median lethal concentrations and maximum ineffective concentrations for a 96-h exposure were calculated. The maximum ineffective concentrations of metals did not exceed their background levels in Peter the Great Bay (Sea of Japan) but were markedly lower than the maximum permissible concentrations (MPC) set for waters of the seas of the Russian Federation. The prelarvae of the Japanese anchovy and the sand flounder can be useful for evaluation and comparison of the toxicity of pollutants and for the estimation of regional MPC levels for pollutants of marine waters.

This paper presents data on the first record of Ulca bolini . The fish was caught at a depth of 280–300 m in the Sea of Okhotsk off the Kuril Islands (Prostor Bay, Iturup Island). It was 60 cm in fork length (FL) and 7 kg in weight.