Vendace (Coregonus albula) is a freshwater species found in brackish water in the northern Baltic Sea. It has been most abundant in the northernmost part of the Gulf of Bothnia and in the easternmost parts of the Gulf of Finland (GoF), where the stocks have been declining. We assessed the level of genetic diversity and differentiation among the vendace populations in the GoF and adjacent areas. We analysed a total of 385 vendace samples from eight sampling sites. All the samples were genotyped at 17 microsatellite loci. Levels of genetic diversity were generally high within the sampled vendace populations, but the genetic differentiation between the populations was relatively low. The vendace population in the easternmost GoF is genetically close to the freshwater vendace of Lake Ladoga, flowing into the GoF via the Neva River. A previously known local vendace population in Virolahti Bay, on the Finnish coast 150 km west of the mouth of the Neva River, appears to have become extinct during the last 30-40 years. In the Pyht & auml;& auml; archipelago, close to the mouth of the Kymijoki River, there is still a small local vendace population, which is genetically close to the sea-spawning vendace population in the Bothnian Bay. This still genetically viable Pyht & auml;& auml; population evidently carries the genes of a sea- or estuarine-spawning ven-dace that, based on observations from the previous century, sporadically occurred along the entire Finnish coast. This population is an important part of the local fish biodiversity

This article presents data on the mesonephros histology and ultrastructure in the Atlantic salmon from the Baltic Sea and Barents Sea populations, with an emphasis on comparisons between the following ontogenetic stages: parr, smolting, adult life at sea, the adults ' return to their natal river to spawn, and spawning. The ultrastructural changes in the renal corpuscle and cells of the proximal tubules of the nephron occurred as early as the smolting stage. Such changes reflect fundamental alterations during the pre-adaptation to life in saltwater. In the Barents Sea population, the adult salmon sampled in the sea had the smallest diameters of the renal corpuscle and proximal and distal tubules, the most narrow urinary space, and the thickest basement membrane. In the group of salmon that entered the mouth of the river and spent less than 24 h in freshwater, the structural rearrangements occurred only in the distal tubules. Better development of the smooth endoplasmic reticulum and a greater abundance of mitochondria in the tubule cells were observed in the adult salmon from the Barents Sea compared to those from the Baltic Sea. Cell-immunity activation was initiated during the parr-smolt transformation. Another pronounced innate-immunity response was registered in the adults returning to the river to spawn.

The study focuses on the microanatomy and ultrastructural changes in the trunk kidney interstitium cells and nephrons in parr, smolt, and spawning brown trout (Salmo trutta Linnaeus, 1758) sampled in Luga River and Solka River, the tributaries of the Baltic Sea. Regardless of the type of cells or their structure, there were changes in their areas and in the number and structure of organelles responsible for the transport, synthetic, and energetic functions of cells. Our data on the morphology of the nephron combined with data on its physiology suggest a fundamental change in kidney function during the parr–smolt transformation before migration; this could be a pre-adaptation for a successful life in saltwater where urine output is sharply reduced. Thus, detected structural features of the trunk kidney in S. trutta are cytological markers of the migration process. The numbers of lymphocytes, neutrophils, and eosinophils with segmented nuclei increased from parr to smolts and then to spawners; only monotypic specific granules in neutrophils were found in smolts and spawners. Cells with radially arranged vesicles were described for the first time in S. trutta renal interstitium. Their origin has not yet been established. The shape of these cells changed from spherical to trihedral during fish maturation. All the above ultrastructural changes of renal interstitium cells could be considered cytological markers of cell maturity.

I conducted a population-genetic study of the Eurasian cisco complex in an area extending from the Baltic Sea to the East-Siberian Sea using 30 enzyme loci. The results indicate that the least cisco (Coregonus sardinella) populations from most rivers of the Kara, Laptev and East-Siberian sea basins are genetically fairly homogeneous, and that the cluster they form is different from the one for the vendace (C. albula) populations from the waterbodies of the Baltic and White seas (Nei's genetic distance (DN) = 0.076). The least cisco and vendace originated from two major phylogenetic lineages of the species occurring as the purest form in the above regions. As a result of the evolution and complex interactions among local populations within the two phylogenetic lineages of cisco at the various stages of Middle and Late Quaternary glaciations, most extant modern populations are hybrid in origin. For example, the Barents Sea populations and the easternmost population from the East-Siberian Sea basin (Kolyma River) emerged as a result of hybridization during the last colonization wave by the least cisco (East Siberian) along the Arctic coast upon cisco's interaction with local ciscoes in the west and east. The White and Kovzhskoye lake populations from the Caspian Sea basin, which form a joint cluster with them, are the hybrids of the local vendace and the descendants of the first wave of least cisco's (West Siberian) expansion to Europe. In this paper, I also discuss the most probable scenarios of cisco's colonization of the study area using paleolimnological reconstructions.

In Lake Onega, the whitefish Coregonus lavaretus has been shown to occur as a variety of forms. Medium- and sparsely-ranked whitefish are most abundant. Analysis of available data indicates that whitefish populations from Karelia's large lakes display the maximum values of various genetic variability indices. This fact seems to be due to the history of the colonization of the lake by the discrete evolutionary whitefish lineages from various Late Quaternary habitats followed by their hybridization. A great variety of Onega whitefish haplotypes is probably related to the genetic heterogeneity of the whitefish who until recently had occurred as five ecological forms ranking as subspecies. The median network obtained suggests that many of the populations studied have become less abundant. The well-defined "star-like" network structure is characteristic of populations that passed through a narrow "bottleneck" in the near past and then expanded rapidly, as indicated by the abundance of rare haplotype varieties. It seems that the retreat of the Scandinavian glacier was not a momentary event but took a long time during which the populations formed were subjected to demographic transformations.

In the eastern Gulf of Finland, European smelt Osmerus eperlanus occurs as an anadromous ecological form that spawns in coastal, low-salinity zones and in several rivers entering the gulf, most importantly in the River Neva. Osmerus eperlanus is a key commercial fish species for the population of St. Petersburg, and the city's fish symbol. However, the state of the smelt stock has considerably deteriorated over the past few decades. Monitoring shows that annual catches during 1965-1992 averaged 2274 t, compared to 292 t in 2002-2017, although some improvement is inidicated by a gradual increase in catches in recent years (e.g., to 595 t in 2017). This paper addresses long-term and recent changes in the fisheries for smelt in the eastern Gulf of Finland, including both commercial and recreational fisheries, and the range of fishing gears used. The commercial smelt fishery is mainly conducted during the spawning period (April-May) on migrating fish, using trap nets of various designs and beach seines. There has been an increase in recreational fisheries for smelt; in years when ice cover on the gulf during winter (December-April) is steady, recreational fishers from St. Petersburg, using hook and line, may catch quantities that are comparable to those of commercial catches. Several factors may account for the stock dynamics and associated changes in catches of smelt: these include a decrease in prey availability in the gulf; loss and degradation of spawning and nursery habitats, partly associated with large-scale hydroengineering operations in Neva Bay; and illegal, unreported and unregulated (IUU) fishing which became widespread in post-Soviet decades. In spite of a gradual increase in smelt abundance in the most recent 15 years, a failure to accurately monitor and manage the extent of IUU and recreational fishing for smelt, to assess the status of the stock, or to forecast catches, increases the risk of overfishing of the spawning stock.

The Pacific smelt Osmerus dentex is widely distributed in the North Pacific and Arctic seas and belongs to the species that may shed light on the biogeography and evolutionary history of Arctic marine fauna. O. dentex came into existence in the northwestern Pacific at the Pliocene–Pleistocene border and could widely spread along the Eurasian and North American coasts. We assessed the impact of global climatic and geological changes on the formation of the genetic structure of O. dentex in the Eurasian parts of the species area using a variety of phylogenetic methods and molecular dating. The results were interpreted in conjunction with paleoclimatic evidence. Phylogeographic patterns based on cytb and coI sequences, and RFLP ND3/ND4L/ND4 and A8/A6/COIII/ND3 mtDNA regions for 462 Pacific smelts from 25 Eurasian locations were analyzed. Our results suggest that (1) geographical distribution observed for mtDNA haplotypes resulted from influences of historical range expansions, episodes of long-distance colonization and restricted dispersal; (2) the main refugium was located in the northwestern Pacific and the genetic similarities observed among and within geographical regions probably originated from postglacial recolonization from common sources; (3) an additional small refugium in the White Sea existed in the Late Pleistocene.

Background. A population genetic study of Siberian whitefish or pidschian Coregonus lavaretus pidschian Gmelin of the Anabar River (North-West Yakutia) has been done to study genetic structure of the species within a river system and for revealing its phylogeographic relations. Materials and Methods. Five samples of pidschian from different parts of the river were analyzed for 30 isozyme loci. Results and Discussion. The results has demonstrated a significant genetic heterogeneity of the species sampled from lower and middle reaches of the river (0.001 DN 0.056). The most likely reason for genetic differentiation of the species within the river system is a colonization of the watershed by independent phylogenetic lineages of whitefish. At present the phylogenetic lineages in Anabar River are presented by sympatric ecological forms of the species eastern-siberian whitefish and glacial-plains whitefish which maintain their reproductive isolation. The relationships of ecological forms of whitefish dwelling the Anabar River with other populations of the species in Siberia, and possible ways of penetration of discrete phylogenetic lineages of pidschian in the basin of studied river are discussed. Conclusions. A genetic heterogeneity of whitefish from Anabar River should be taken into account while creating adequate intraspecific taxonomy and considered in conducting fisheries and environmental measures.

The paper describes changing patterns of commercial fish catch in the downstream part of the Neva River and the eastern Gulf of Finland and analyzes drivers of these changes for the period 1929–1995. We summarize catch data on 20 species and species groups of fishes and lamprey, as well as available abiotic data (salinity, temperature and water transparency). Water transparency gradually decreased during the 20th century being inseparable from a number of non-quantified anthropogenic factors, thus it can be used as an integral index of anthropogenic loading on the ecosystem. Because fisheries statistics were not published regularly, catch data were extracted from archives and various publications. Fishing locations, gear and target species changed over time in relation to each other, reflecting technological developments in fisheries, commercial demands for fishery products and the abundance of fish populations. Until the 18–19th centuries, fisheries took place mostly in rivers where weirs and set nets targeted sturgeon, salmon and whitefish. By the end of the 19th century, herring and smelt were the main targets of fixed nets in coastal areas. A century later, the main commercial species, herring, was harvested with pelagic trawls operating offshore in the Gulf. This evolution in fisheries, along with other anthropogenic activities, caused severe declines in diadromous species. Spawning migrations that make them easy to catch, and their high market value, make diadromous fish more vulnerable than other groups. Canonical correspondence analysis showed that catches of most diadromous species decreased with increasing transparency, which may reflect their response to anthropogenic pressure. Marine and freshwater fish suffered from anthropogenic pressure, but to a lesser extent probably because of a wider distribution and dispersal, and more capital-intensive fishing methods. Catches of marine species, except herring, significantly increased in the 1970–1980s when salinity was comparatively high. We found no correlation of fish catches with temperature.

A population genetics study of coregonid fish species from the Russian Arctic using 30 enzyme loci demonstrated that Siberian endemic species (Coregonus peled (Gmelin 1789) and C. muksun (Pallas 1814)) as well as species with distributions limited by the Holarctic at the edges of western North America and Eastern Europe (broad whitefish C. nasus (Pallas 1776) and Arctic cisco C. autumnalis (Pallas 1776)) are rather homogeneous along the whole Arctic shoreline. In contrast, circumpolar coregonid species (European whitefish C. lavaretus (Linneaus 1758) and the vendance complex of European cisco C. albula, C. sardinella (Valenciennes 1848)) feature stronger genetic divergence among populations in the same region and patterns of genetic diversity showed a significant consistency across species with minimal variations identified between the species from the farthest Eastern European population (the Pechora River) and the outermost eastern populations of Eastern Siberia (the Kolyma and the Indigirka Rivers). It was hypothesised that modem populations of whitefishes and ciscoes from Eastern Sibirian and Eastern European Subarctic shores are the remains of a former more or less integral fauna of these species which may have developed differently during the Pleistocene in Siberia and adjacent areas, perhaps by large-scale merging of periglacial lakes and their discharges via desalinated segments of the sea or during the course of the ice regression period via merging of the lower sections of neighbouring rivers. In the Late Pleistocene, a relatively homogeneous fauna of whitefishes and ciscoes of the Arctic area was fragmented as a result of the advance of the glaciers and the ousting of the fauna of the Arctic fishes to its southern periphery with postglacial colonisation by the forms of those species that evolutionarily could have been established in the region of Lake Baikal and adjacent mountainous territories. Postglacial expansion of these forms towards the Subarctic coast coincided with the recovery of the flow of the largest Siberian rivers (01), Yenisei and Lena) with the hydrographic network of upstream sections having been changed drastically as a result of complicated geological processes that took place in the south of Siberia.

The White Sea Kuloi plateau is a territory (about 25,000 km(2)) at the southeastern part of the White Sea basin. On the mainland, it is confined by the rivers of the Northern Dvina, the Pinega, and the Kuloi. The fauna of coregonid fishes on that territory is represented by European whitefish (Coregonus lavaretus) and local cisco (genera Coregonus), the species definition of which is still under discussion. We have investigated genetic variability of several whitefish and cisco populations by 29 allozyme loci with the aim to identify the ways of their formation during the postglacial period. Comparison of four cisco populations with several populations of typical vendace (Coregonus albula) from the basin of the Baltic Sea and hybrid forms of vendace and least cisco (Coregonus albula x Coregonus sardinella) from the Pechora has shown that the cisco of the White Sea basin belongs to the species Coregonus albula. Most probably, those populations were formed with no impact from least cisco, which did not reach the basin of the White Sea during the period of postglacial resettlement to the west. The results of comparative studies of whitefish populations have shown that most populations of the White Sea Kuloi plateau emerged due to postglacial colonization of water bodies by common periglacial whitefish race, which usually features lower number of gill rakers and dwells in partly desalinated sea water. The origin of the high-density rakered population from the central part of the White Sea Kuloi plateau-having the biggest deviations from the other populations analyzed in that region-can be explained by both a sympatric and allopatric speciation model.