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— The population genetic structure of Pacific herring Clupea pallasii in the northwestern Pacific Ocean is studied based on the polymorphism analysis of 11 microsatellite loci. Significant genetic differences are found between lacustrine and marine forms of herring ( F ST 0.0197−0.0521). The herring of lakes Ainskoe and Vilyui are separate populations. Based on the genetic differentiation index F ST (0.0086−0.0218), the samples of marine forms are divided into two geographical groups: the Sea of Okhotsk and the Sea of Japan group, and the Bering Sea group. Within these groups, five population groups are differentiated: (1) Peter the Great Gulf, (2) northwestern Sea of Okhotsk (Okhotsk), (3) Shelikhov Gulf Shelikhova (Gizhiginsk), (4) Karaginsky Gulf, and (5) northern Bering Sea. During a period of high abundance, herring lacks clear ecological boundaries; its population structure can change over several generations on a significant part of the distribution range. The modern population structure of the marine forms was formed by a depression of the Bering Sea population and a population explosion in the Sea of Okhotsk.

Based on the analysis of the current distribution, the results of the molecular genetic study into the diversity of the mtDNA region (the first subunit of the cytochrome c oxidase I gene ( COI )) in the samples of the blue hake Antimora rostrata and the Pacific flatnose A. microlepis , and the generalization of literature data on fossil records of morids (Moridae), a scheme for hypothetical spreading of these species in the oceans is presented.

Historical and modern data on the taxonomic status, external morphology, distribution features, biology, economic importance, history of fishing, conservation status, and protection measures for the Caspian lamprey Caspiomyzon wagneri are presented . The Caspian lamprey is an endemic species and the only anadromous lamprey in the Caspian Sea basin. The abundance of this species has declined everywhere; as a result, the species nowadays is on the verge of extinction. Being an important target of fishing in the past, the Caspian lamprey has completely lost its economic importance. It is subject to serious threats of an anthropogenic nature. Constructing of locks and dams without fish passages that prevent spawning migrations, water pollution, dredging and mining of sand and gravel leading to the destruction of habitats and spawning grounds, poaching and lack of legal protection mechanisms are the main threats for this lamprey species.

The phylogeographic analysis of Gadus chalcogrammus from the Asian part of the range (the western part of the Bering Sea, the Sea of Okhotsk and the Sea of Japan, the Pacific waters of the Kuril Islands and Kamchatka) based on data on the polymorphism of the mtDNA control region fragment ( D-loop , 526 bp) was performed for the first time using large-scale material (1162 individuals from 38 samples). The obtained results indicate the existence of two large groups in the surveyed water area: one is localized in the western part of the Bering Sea, and the other is formed by samples from the Sea of Japan and the Sea of Okhotsk and from the Pacific waters of the Kuril Islands and Kamchatka. An unusually low level of polymorphism in the mtDNA control region of Gadus chalcogrammus was revealed, which was also previously found in G. macrocephalus and is probably due to similar microevolutionary processes that took place in the past in both species.

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.

Polymorphism in the variable fragment of the mtDNA control region (D-loop, 373 bp) and four microsatellite loci in 683 specimens of the Pacific herring Clupea pallasii sampled at different locations from the Asian part of range has been studied. It is shown that the Pacific herring lake forms inhabiting the three lakes on Sakhalin Island (Ainskoe) and in the Kamchatka Peninsula (Vilyuy and Nerpiche) have significantly diverged from the marine forms according to the data on the mtDNA and nDNA markers. The genetic variations among the herring forms inhabiting different lakes ( F ST = 0.034−0.066) and between the lake herring forms and marine herring forms ( F ST = 0.004−0.055) are revealed. The level of the genetic differentiation among the lake herring forms is much higher than that among the samples of the marine herring forms, which may be explained by the founder effect. Evolution of the lake forms occurred along with the geological processes producing the lakes.

— Six groups have been identified in the species' population structure based on the analysis of microsatellite markers' polymorphism in Pacific cod Gadus macrocephalus samples within the entire western part of the North Pacific, including waters of the Pacific coast of Canada. The first group includes cod from waters of the Yellow Sea; the second group consists of cod from the Sea of Japan (eastern coast of Korea and Peter the Great Bay); the third group combines cod from Tatar Strait and the South Kuril Islands (both Sea of Okhotsk and Pacific Ocean sides); the fourth group is formed by cod from the northwestern Sea of Okhotsk and Taui Bay; the fifth-largest group includes cod from waters off western Kamchatka, the North Kuril Islands (Sea of Okhotsk and Pacific Ocean sides), Karaginsky Bay, Navarinsky area in the Bering Sea, and Anadyr Bay; the sixth group is formed by cod from coastal waters of Canada.

Data on the age and growth of the roughhead grenadier Macrourus berglax from waters off Southwest Greenland have been obtained based on the analysis of otoliths. Specimens with a preanal length of 5−39 cm, a weight of 7−5275 g, and age from 2 to 22 years are recorded in trawl catches. Roughhead grenadier exhibits a similar rate of linear growth in waters off Southwest Greenland and other parts of the range in the Northwest Atlantic. No considerable differences from the rate of the linear growth calculated earlier from scales for the species in waters off West Greenland have been found. In the recent period, the rate of weight gain in roughhead grenadier in waters off Southwest Greenland has been lower than in the Northwest Atlantic in the first half of the 1980s. The age of mass maturation in males (7–9 years) and females (16–17 years) in waters off West and East Greenland is somewhat higher than in coastal waters of Norway and the Northwest Atlantic.

The species status is justified for the Okhotsk lumpsucker Eumicrotremus ochotonensis based on the morphological characters. The differences from the closely related species E. derjugini inhabiting the Arctic Ocean are given. Two species were redescribed basing on type series, their diagnoses were clarified, and the lectotypes were designated. Intraspecific variability is discussed using new materials from the Barents, Kara, Laptev, and Okhotsk seas. The two species differ markedly in a complex of morphological features (shape of the submerged dorsal fin, proportions of the body, number and location of bony plaques) and characteristics of biology (spawning season). The modern disjunction of the ranges of E. ochotonensis and E. derjugini covers the Bering, East Siberian, and Chukchi seas. Sequence analysis of the cytochrome oxidase ( COI ) gene fragment of mtDNA revealed differences in the haplotypic diversity of the two species. Weak genetic divergence between species indicates a relatively recent isolation of E. derjugini and confirms its status of the evolutionary young species.

Samples of Greenland halibut Reinhardtius hippoglossoides (Jordan and Snyder, 1901) from the Atlantic, Arctic, and Pacific Oceans were compared using eight microsatellite loci and the Cyt b mtDNA gene. The data obtained revealed a population connectivity of the Greenland halibut from the Laptev Sea to those from the Atlantic Ocean that is result of considerable eastward range extension due to recent climate change. Genetic differences between the Greenland halibut groupings of the Atlantic and Pacific Oceans, according to F st values (0.141–0.197), reach a high level. Given the genetic differences revealed by both nuclear and mitochondrial markers, the taxonomic status of the Greenland halibut inhabiting the Pacific Ocean requires reevaluation at least to the rank of subspecies. It is suggested that the Greenland halibut populations of the Atlantic Ocean basin originated from those of the North Pacific. The time and conditions of Greenland halibut penetration from the North Pacific to the Atlantic Ocean are discussed.