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An isolate tooth of a rare extinct hook-toothed mako Cosmopolitodus planus (Agassiz, 1856), discovered in the Lower Miocene deposits of the Chekhov Formation of Sakhalin Island is described. This extinct species was distributed exceptionally in the Pacific basin, and is known mainly from the deposits of the Middle and Upper Miocene. Thus, the described tooth is, probably, the oldest record of this species. The geographic and stratigraphic distribution of this species, as well as the validity of the genus Cosmopolitodus Glickman, 1964, are discussed.

Shortcrevice eelpout Gymnelopsis brevifenestrata (Zoarcidae, Gymnelinae) is an endemic species of the Sea of Okhotsk; until recently, it was known by 12 type specimens from the museum collections. The variability of the species was characterized and its distribution was revised by the study of several new specimens and paratypes. The live coloration of males is described for the first time, giving new characters for the field taxonomic identification of this species. G. brevifenestrata inhabits the western and northern Sea of Okhotsk at the depth range of 76–200 m. Considering the association of G. brevifenestrata to supercooled waters, it should be assigned to the glacial group of Okhotsk-sea species.

In the deposits of the Middle–Late Miocene of the deep-water Kurasi Formation of Southwestern Sakhalin, a destroyed skeleton of the wolffish head Anarhichadidae gen. et sp. indet. was found. This is the most ancient find of the fossil representative of the family. The features of the dentition of the lower jaw and the vomer of the Miocene fish is similar to those of a modern Atlantic species: spotted wolffish Anarhichas minor .

Phylogenetic morphological, and molecular analysis of lumpsuckers of the family Cyclopteridae is carried out. The cladograms reveal the validity of three subfamilies within the family Cyclopteridae: Cyclopterinae, Aptocyclinae, and Eumicrotrematominae. Five valid genera ( Cyclopterus , Aptocyclus , Cyclopsis , Lethotremus, and Eumicrotremus ) are revealed, and the genus Cyclopterus is accepted as the most generalized within the family Cyclopteridae. The genus Lethotremus is separated from the species of the genus Eumicrotremus , and, thus, the generic status of the former genus is restored. The taxonomic position of E. soldatovi is discussed. Based on the presence of a large number of monotypic genera among generalized clades of lumpsuckers, they could represent the remains of the former widely distributed fauna with a weak development or absence of external armament. The forms of the genus Eumicrotremus with a good armament represent a comparatively young group of weakly differentiated species. Several heterochronies of the paedomorphic and peramorphic types are revealed in the evolution of the family Cyclopteridae.

A new species of the Recent genus Enophrys , E. hoplites sp. nov., is described from the Miocene (Serravalian‒Tortonian) Agnevo Formation of Sakhalin Island, Russia. This Miocene species differs from two Recent congeners in the greater number of anal fin rays (14 versus 9‒13), the smaller head, less raised margins of the orbit, flatter upper contour of the head, longer anal fin base, short predorsal distance, higher first dorsal fin, and in the right angle (versus acute angle) between two upper preopercular spines. An archaic feature of the new species is the presence of two rays on the posterior pterygiophore of the anal fin, a character recorded only in the most primitive Recent members of the family. The occurrence of this new fossil species shows that extant subfamilies, tribes, and genera existed as a part of the family Cottidae as early as the Miocene time.

The first Russian record of fossil bristlemouth from the Middle-Late Miocene of Sakhalin Island (Kurasi Formation) is reported and described as a new species, Cyclothone mukhachevae (Pisces: Gonostomatidae). The new Miocene species is similar in pigmentation, proportions, and metric characters to the group of Recent black bristlemouths. The short base of the dorsal fin resembles that of living C. atraria . The new species differ from the latter in the somewhat fewer teeth in the maxilla and the posteriorly displaced beginning of the dorsal fin base relative to the beginning of the anal fin (vs. at the same level). The geographical range of C. atraria is closest to the locality of C. mukhachevae among other species of Cyclothone . This indirectly corroborates the assumption that morphological similarity of the two species results from their close relationship.

A juvenile of the deep-sea smelt Leuroglossus kobylianskyi from the Miocene of Sakhalin Island is described for the first time. In color features, juvenile L. kobylianskyi is similar to fry of extant L. schmidti. It is shown that the bone skeleton and color of L. kobylianskyi developed at a higher rate than in L. schmidti.

This article documents the first mass capture (over 300 individuals per catch) of black snake mackerel Nealotus tripes (Gempylidae) in the open part of the northwestern Pacific to the southeast of the southern Kuril Islands in September 2014. The external morphological characters and the size composition of the black snake mackerel, and the species composition of hydrobionts that occur together with mackerel in catches are characterized.

The skeletal structure of the Southern Ocean daggertooth ( Anotopterus vorax ) has been studied for the first time. It generally corresponds to the A. pharao skeleton, as it has been previously described. The discrepancies pertain to the authors’ other various data on both the details of the structures of branchial arches, maxillae, cranium, and axial skeleton and the traits of the Anotopterus genus, which have not been described earlier. They include the availability of a considerable number of bony ribs (epineurals and epicentrals) attached to the neurocranium bones (epiotic, intercalar, and exooccipital) and some elongated and discontinuous lateral keel bones located on both sides of the central keel bone. Cladistic analysis has been performed with the finding that the A. vorax is united with the A. pharao and the Polymerichthys fossil genus into one clade, which takes an intermediate status between the representatives of the Alepisauridae and Paralepididae families. The assumption has been made about the necessity for the restitution of the family status of Anotopteridae.

The redescription of Eumicrotremus andriashevi Perminov, 1936, and designation of the new subspecies Eumicrotremus andriashevi aculeatus Voskoboinikova et Nazarkin ssp. n. (Litke Strait, Bering Sea) have been performed. E. andriashevi aculeatus differs from the nominative subspecies by the presence of larger and higher bone plaques that form the “cheeks” and make the external view of the fish “disheveled” and by the larger body height and smaller snout length, as well as by the shape of the infraorbitals and mesethmoideum.