Growth,size-age structure of catches and reproduction of the Volga zander <Emphasis Type="Italic">Sander volgensis</Emphasis> (Percidae) in the upper part of the Volga stretch of the Kuibyshev Reservoir

Conditions of reproduction, size-age structure of catches, and the growth of the Volga zander Sunder volgensis in the upper part of the Volga stretch of the Kuibyshev Reservoir from 2002 to 2007, as well as its fishery in this water body, are considered. A decrease in catches of the proportion of large elder age groups of the Volga zander in the period of destabilization of the reservoir ecosystem, as compared to the phase of its relative stabilization from the 1970s to the 1980s, and a decrease in the commercial catch were established. Besides, retardation of its growth in connection with the deterioration of the ecological situation is observed, but the average level of reproduction is retained, which at the organization of rational fishery can lead to the restoration of the Volga zander stock.     

Comparative biological characteristics of zander <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.) in Lakes Onega and Vygozero

The work on the introduction of the zander Sander lucioperca (L.) from Lake Onega to Lake Vygozero is reviewed. A comparative analysis is performed for the biological parameters of zander from these lakes. The zander population from Lake Vygozero differs from that of Lake Onega in its lower growth rate, later maturation, and lower fat content of internal organs; these differences are determined by the limnological parameters and food supplies of both waterbodies.     

Dynamics of structural indices of populations of zander Stizostedion lucioperca (Percidae) of the Rybinsk Reservoir for 1954–2010

Data on the age and size dynamics, linear and weight growth, and feeding of zander Stizostedion lucioperca collected in the Rybinsk Reservoir in 1954–2010 were generalized. The main factors determining the numbers of zander population and causing changes in its structural indices are the intensity of fishery and feeding conditions. Beginning from the mid-1990s, commercial load considerably exceeds the adaptation possibilities of the zander population; under the impact of this factor, its numbers declined, and the age structure changed towards the domination of individuals of junior ages. Introduction of the Black-Sea sprat Clupeonella cultriventris along with of climate warming led to negative changes in the populations of prey fish, as a result of which the proportion of their own juveniles increased in the feeding of adult zander. During recent years, zander fingerlings throughout summer cannot pass to predatory feeding, which leads to a decrease in the rate of linear and weight growth of mature individuals.     

Specific features of feeding in underyearlings of zander (<Emphasis Type="Italic">Sander lucioperca</Emphasis>) (Percidae) of the Rybinsk reservoir in various years

The results of the studies on feeding of zander (Sander lucioperca) underyearlings in the Rybinsk Reservoir in 2008-2010 and 2012 are presented. The study revealed that, at feeding on plankton, the assemblage of the organisms consumed by juvenile zander has not been changed compared to 1950. The underyearlings prefer to feed on large zooplankters—Daphnia longispina, Leptodora kindtii, and Bythotrephes longimanus—along with copepods. At some sampling stations, the species of macrozoobenthos were included in the young zander food. The piscine component of zander food was dominated by underyearlings of Azov-Black sea tyulka (Clupeonella cultriventris); the fries of perch (Perca fluviatilis) and cyprinids (Cyprinidae) were less important. The feeding strategy of zander underyearlings was unchanged in various years. At turning to predatory feeding, not only the ratio of sizes of predator versus prey but also the proportion of the densities of their populations plays an important role.     

Dynamics of species composition of fish and some results of ichthyomonitoring in the middle course of the Oka (Ryazan oblast)

The dynamics of species composition of fish from the middle course of the Oka is considered. A total of 53 species of Cyclostomata and fish was previously recorded; however, only 43 species have been found at the present time. Due to different causes, ten species have disappeared, and ten new species have emerged. The species composition and structure of aboriginal fish population are characterized by relative stability; however, the total abundance of fish during the current decade, as compared to the 1970s, has considerably decreased. The sterlet Acipenser ruthenus, lake minnow Phoxinus precnurus, Volga zander Sander volgensis, and freshwater sculpin Cottus gobio belong to rare fish.     

On the populational structure of sterlet <Emphasis Type="Italic">Acipenser ruthenus</Emphasis> (Acipenseridae) from the Volga Lower reaches

Trawl surveys made in the Lower Volga and the Caspian Sea revealed that the full life cycle of the Lower Volga sterlet is confined to fresh water and only single specimens living in the Volga-Caspian canal can live in the canal and swim to weakly saline and stagnant waters. Therefore, the sterlet living in the Volga-Caspian canal with its expressed current should be attributed to potamodromous forms. In consideration of the data on distribution, the variation of the complex of plastic characteristics, growth rate, and infestation with the parasite Amphilina foliacea it is concluded that within the Lower Volga population of sterlet three populations of the lower rank may be discerned: the Volgograd population living from the Volgograd Hydroelectric Complex dam to the Kamennyi Yar settlement; the eastern population living in the top of the Volga Delta and Buzan channel; and the western population in the Volga-Caspian canal. These populations differ in some plastic characteristics, linear growth rate, the part of fish infested with the parasite A. foliacea, and in the occurrence of anomalies in the structure of mature ovicells.     

Can juvenile Baltic sturgeon (Acipenser oxyrinchus) smell the enemy?

Atlantic sturgeon (Acipenser oxyrinchus), also known as Baltic sturgeon, is considered extinct in German waters. Fish‐rearing for conservation purposes largely relies on classical hatchery technology focusing on traits like survival and growth in captivity but rarely focusing on subsequent life in the wild, lacking skills such as foraging or anti‐predation behavior. Predation is hence a major factor for mortality in newly stocked individuals. The aim of this study was to evaluate if naïve Baltic sturgeon juveniles were able to recognize a common predator—zander (Sander lucioperca)—by olfactory cues and adapt accordingly. Over a period of 30 days, Baltic sturgeons were supplied with effluent water from a rearing tank with zander (zander unit) and, as a control, carp (carp unit), three tanks each. Distribution within the tank, morphology of the dorsal scutes, stress (glucose, lactate and cortisol) and gene expression of brain plasticity and cognition were studied in comparison to the control group (carp unit). No significant differences between the zander and the carp unit were observed in any of the parameters measured. Thus, we conclude that naïve Baltic sturgeon is not able to innately recognize potential predators by olfaction alone. Therefore, future studies should focus on applying predator odor together with chemical alarm substances.     

Chromosomal polymorphism in the populations of malaria mosquito <Emphasis Type="Italic">Anopheles messeae</Emphasis> (Diptera,Culicidae) in the Volga region

We studied the species composition and chromosomal variability of malaria mosquitoes in the Volga Basin (Upper, Middle, and Lower Volga regions). We investigated larvae karyotypes of sibling species of the Anopheles maculipennis group. We calculated the frequencies of chromosomal inversions in the local populations of the dominant species An. messeae. We discovered that karyotypic structure of An. messeae populations depends on landscape-climatic zones. Populations of the Upper, Middle and Lower Volga differ in frequency of chromosome inversions XL, 2R, 3R, and 3L.     

On the distribution of riffle minnow <Emphasis Type="Italic">Alburnoides bipunctatus</Emphasis> (Cyprinidae) in the Volga Basin

On the basis of analysis of our own and published data on the distribution of the riffle minnow Alburnoides bipunctatus rossicus in rivers of the Volga Basin, the eastern boundary of the range of this subspecies included in the Red Data Book of the Russian Federation is specified. It is shown that A. bipunctatus is widely distributed in the entire basin of the Middle Volga and Kama, except the extreme northeast (mountain tributaries of the Upper Kama upstream the Chusovaya River), and rarely occurs in the Upper Volga Basin. The Tereshka River (Ulyanov oblast) and Chapaevka (Saratov oblast) should be considered the southern boundary of the distribution of the subspecies in the Volga Basin. Since the mid-1990s, a drastic and uniform increase in the number of findings and the abundance of A. bipunctatus is recorded. This species has become a common fish in many rivers and, in some cases, a dominant species in river ichthyocenoses. Possible causes of these changes are discussed, and a conclusion is made concerning the need of the revision of the status of the subspecies A. bipunctatus rossicus.     

Stock status and current tendencies in the population dynamics of commercial fishes of Pskov-Chudskoe water body

Dynamics of eight commercial populations of fish from Pskov-Chudskoe Lake forming the main bulk (up to 80%) of annual catch was analyzed using an ADAPT-VPA model making it possible to reconstruct the dynamics of the total stock biomass and fishing mortality. The populations of five species (European smelt Coregonus albula, whitefish C. lavaretus maraenoides, perch Perca fluviatilis, roach Rutilus rutilus, ruffe Gymnocephalus cernuus) in the present period demonstrate a tendency for a decrease in biomass while the stocks of two species (bream Abramis brama and zander Sander lucioperca) beginning from the 1980s considerably increased. A particularly drastic (multifold) increase in biomass is recorded in zander population. The causes of the observed population changes are related mainly to ecosystemic transformations taking place in the water body; only with respect to two species-perch and roach-can one state that the decrease in stocks is determined in part by the fishery impact. The increase in zander population is, in all probability, the result of the combined effects of eutrophication forming favorable conditions for the feeding and survival of its juveniles and fishery that led to the decrease in the biomass of one of its main food competitors-perch. The drastic increase in zander numbers in turn promoted the decrease in the biomass of species being objects of its feeding.     

Reproductive parameters of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) from the Rybinsk Reservoir reaches differing in anthropogenic loads

The results of a study on the parameters of reproductive capacity in roach from the Sheksna and the Volga reaches of the Rybinsk Reservoir are presented. The Volga reach is relatively clean, while the Sheksna reach is subject to the strongest anthropogenic load. In 2011, the average values of the absolute and relative fecundity, as well as the egg size, in roach Rutilus rutilus (L.) from the Volga reach were higher than those in roach from the Sheksna reach, but differences are mainly statistically insignificant. The data of the study indicate the adaptation of the investigated roach to the negative influence of the Sheksna reach contamination and, in particular, its preservation of a sufficient level of reproductive capacity.     

First Year Ontogenetic Diet Patterns in Two Coexisting <Emphasis Type="Italic">Sander</Emphasis> Species, <Emphasis Type="Italic">S. lucioperca</Emphasis> and <Emphasis Type="Italic">S. volgensis</Emphasis> in Lake Balaton

First year ontogenetic diet patterns and size-dependent diet partitioning of two coexisting piscivorous percids, pikeperch and Volga pikeperch were analysed in Lake Balaton. Diet patterns of the two pikeperches followed a common trend, catching larger preys at larger sizes, but in details they were different. Until 20–30 mm size age-0 pikeperch fed on planktonic microcrustaceans and were found only in the pelagic zone. After this size, from the end of May, a part of the stock shifted habitat and moved to the littoral zone to feed on Limnomysis benedeni. Majority of the stock stayed in the pelagic zone and shifted to Leptodora kindtii. In the pelagic group early piscivory, mainly cannibalism, occurred only sporadically. However, the few individuals that reached 100 mm size during the first year were typically piscivorous. Volga pikeperch stayed in the pelagic zone during the first year and shifted from planktonic microcrustaceans to benthic macroinvertebrates. General patterns of the first year diet ontogeny were similar in the different areas of Lake Balaton in both pikeperches with only some differences in the secondary food resources, especially in the share of chironomids. Chironomids were eaten at highest ratio by the two fish species in the Keszthely basin in accordance with their abundance pattern. Maximum prey sizes increased significantly with predator size in both pikeperch and Volga pikeperch. However, pikeperch ate much larger prey than did Volga pikeperch at the same size although they have a similar mouth gape to length ratio. These two, closely related pikeperches, although occur in the same habitat and have similar patterns of diet ontogeny, effectively partition food resources in Lake Balaton during the first growing season, except in the very beginning of their ontogeny at L = 5–10 mm size. It appears that age-0 Volga pikeperch is not a significant competitor for the economically highly rated pikeperch in Lake Balaton. On the other hand, it is age-0 pikeperch that might affect Volga pikeperch during its early ontogeny, in the planktivorous stage.     

Study of some meristic features in the Black Sea Caspian Kilka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis>, Clupeidae) introduced in Volga River reservoirs

The results of studies on the morphological variability in kilka (Clupeonella cultriventris) of the Volga River reservoirs are given. In the northward direction in newly established populations, mean values of the number of vertebrae in the truncal part of the backbone (vert. tr.) and total number of vertebrae (vert.) increase. Presumably, the horizontal-stepped cline according to vert. is determined by differences in the thermal regimes in waterbodies during the axial skeleton morphogenesis. Using the principal component analysis by a combination of four features (cs, vert. tr., vert. c., and vert.) three groups of kilka populations were revealed: the upper-middle Volga, the Rybinsk-Sheksna, and the upper Volga. These groups reflect the adaptation process of the invader populations to new environmental conditions.     

Assessment of pathological changes in fish muscle tissue, forming as a result of exposure to toxic factors in the environment

Our investigation of muscle tissue of fishes, inhabiting the regions with unfavorable ecological conditions (the river Volga), permitted to select four types of degenerative changes in muscle tissue. These alterations are associated with both the phylogenetic status of fish species and ecological dispositions of species. Using different methods of investigation several types of muscle destruction were shown. I. Destruction of myofibrillar apparatus (lysis of protofibrils), with sarcolemma remaining intact. II. Destruction of the myofibrillar apparatus, with sarcolemma, T-system, and sarcoplasmic reticulum being disrupted. III. Invasion of muscle fibers by lymphoid cells and macrophages; with sarcolemma being intact. IV. Lysis of sarcolemma by proteolytic enzymes of lymphoid elements; with muscle fibers being disintegrated. The objects of this study were muscle tissues of 8 fish species (Acipenser gueldenstadti, A. stellatus, A. ruthenus, Lucioprerca lucioperca, Esox lucius, Perca fluviatilis, Tinca tinca, Caprinus carpio). The white muscle degeneration followed the patterns of types I and II, while that of red muscles corresponded to types III and IV. White and red muscles of the Chondrostei fishes (sturgeon, stellate, sterlet) undergo destruction more frequently, than muscles of the Holostei fishes (pike, perch, zander, sazan, tench). Degenerative processes of white and red muscles of fish-eating fishes were more obvious than those of herbivorous fishes.     

Effect of feeding under-year zander (Sander lucioperca) on size, body mass and body composition before and after wintering

Zander (Sander lucioperca) is one of the most important fish species in the German inland fishery. As a pelagic predator, zander is able to regulate populations of small cyprinids and perch and is therefore used in ‘top‐down’ projects to directly control the food web. At present, natural waters are mainly stocked with one‐summer‐old zander from pond hatcheries; however, such fish are poor stocking material due to low survival rates, presumably because of their small size. Two groups of 50‐day‐old zander fingerlings reared in a recirculation system (T = 23 °C) were used. For 90 days one group (FG 1) was fed with a commercial dry feed (Trouvit Pro Aqua Brut), and the other group (FG 2) was fed with chironomides (Chironomus spp.). The fat content of the dry feed was increased with fish oil supplemented up to 22%. After the rearing period the FG 1 fishes attained the largest size and fat content. A pond with a surface of 667 m² and a mean depth of 0.8 m was stocked with 24‐tagged zander (12 of each feeding group) for wintering. After the winter period of 176 days, survival rate of each feeding group was 83.3%. The fatty acid composition in the membrane lipids of group 2 changed dramatically. In contrast to previous investigations, presented results indicate that the survival rate is not influenced by fish size (weight and length). The crucial factors for high survival rates of zander during wintering are the crude tissue fat content (>5%) and its fatty acid composition.     

Effect of pH on the proteinase activities in the intestine mucosa,chyme, and enteral microbiota in the piscivorous fish differing in their ecological traits

The effect of pH on the activity of proteinases of intestine mucosa, chyme, and enteral microbiota was studied in three piscivorous fish species of the Rybinsk Reservoir differing in their ecological traits: pike Esox lucius, burbot Lota lota, and zander Sander lucioperca. In all fish species, studied pH of ten is optimal for the functioning of proteinases of intestine mucosa; in chyme proteinases, optimal pH values vary from six to ten. Optimal pH for functioning of proteinases of enteral microbiota is seven for zander and pike; pH of nine, for burbot. High activity of chyme and microbiota proteinases within the diapason of pH values of six to nine is a characteristic of burbot. Relative activity of proteinases of intestine mucosa in all fish species is not more than 15% of the maximal activity; that of chyme and enteral microbiota is lower than 40% in zander, close to 50% in burbot, and 80 and 50%, respectively, in pike. It is suggested that diversity of the patterns of pH-dependence of enteral microbiota proteinases relates to the specificity of microbiota in various ecological zones of the reservoir (littoral, sublittoral, and bathyal).     

Molecular genetic analysis of five extant reserves of black honeybee <Emphasis Type="Italic">Apis melifera melifera</Emphasis> in the Urals and the Volga region

Local populations of the black honeybee Apis mellifera mellifera from the Urals and the Volga region were examined in comparison with local populations of southern honeybee subspecies A. m. caucasica and A. m. carpatica from the Caucasus and the Carpathians. Genetic analysis was performed on the basis of the polymorphism of nine microsatellite loci of nuclear DNA and the mtDNA COI–COII locus. On the territory of the Urals and the Volga region, five extant populations (reserves) of the black honeybee A. m. mellifera were identified, including the Burzyanskaya, Tatyshlinskaya, Yuzhno-Prikamskaya, Visherskaya, and Kambarskaya populations. These five populations are the basis of the modern gene pool of the black honeybee A. m. mellifera from the Urals and the Volga region. The greatest proportion of the remaining indigenous gene pool of A. m. mellifera (the core of the gene pool of the population of A. m. mellifera) is distributed over the entire territory of Perm krai and the north of the Republic of Bashkortostan. For the population of A. m. mellifera from the Urals and the Volga region, the genetic standards were calculated, which will be useful for future population studies of honeybees.     

Range expansion of quagga mussels Dreissena rostriformis bugensis in the Volga River and Caspian Sea basin

In 1992, we discovered populations of the nonindigenous quagga mussel Dreissena rostriformis bugensis in the middle reaches of the Volga River. The same species was found in samples collected between 1994 and 1997 in the Volga delta and in shallow areas of the Northern Caspian Sea. D. r. bugensis always co-occurred with its more widespread congener, the zebra mussel D. polymorpha (Pallas 1771). The quagga mussel's contribution to total Dreissena abundance increased over time in the middle Volga reservoirs and Volga River delta. D. r. bugensis was common in the Volga portion of Rybinsk Reservoir during 1997 and, by 2000, it was in Uglich, Rybinsk and Gorky Reservoirs on the Upper Volga River. D. r. bugensis was neither found in Ivankov Reservoir, nor in terminal sections of the Volga-Baltic corridor including the eastern Gulf of Finland. Presently, all but the northern-most regions of the Volga River have been colonized by D. r. bugensis. We hypothesize that its introduction into the Volga River and Caspian basin occurred no later than the late 1980s via commercial shipping that utilized the Volga-Don waterway to navigate between the source Black-Azov Sea region and recipient areas on the Volga River. Larval drift likely contributed to establishment of populations at downstream sites, while human-mediated vectors may be responsible for introductions to upstream locations on the Volga River. We anticipate continued northward dispersal in conjunction with shipping activities.     

Range expansion of quagga mussels Dreissena rostriformis bugensis in the Volga River and Caspian Sea basin

In 1992, we discovered populations of the nonindigenous quagga mussel Dreissena rostriformis bugensis in the middle reaches of the Volga River. The same species was found in samples collected between 1994 and 1997 in the Volga delta and in shallow areas of the Northern Caspian Sea. D. r. bugensis always co-occurred with its more widespread congener, the zebra mussel D. polymorpha (Pallas 1771). The quagga mussel's contribution to total Dreissena abundance increased over time in the middle Volga reservoirs and Volga River delta. D. r. bugensis was common in the Volga portion of Rybinsk Reservoir during 1997 and, by 2000, it was in Uglich, Rybinsk and Gorky Reservoirs on the Upper Volga River. D. r. bugensis was neither found in Ivankov Reservoir, nor in terminal sections of the Volga-Baltic corridor including the eastern Gulf of Finland. Presently, all but the northern-most regions of the Volga River have been colonized by D. r. bugensis. We hypothesize that its introduction into the Volga River and Caspian basin occurred no later than the late 1980s via commercial shipping that utilized the Volga-Don waterway to navigate between the source Black-Azov Sea region and recipient areas on the Volga River. Larval drift likely contributed to establishment of populations at downstream sites, while human-mediated vectors may be responsible for introductions to upstream locations on the Volga River. We anticipate continued northward dispersal in conjunction with shipping activities.     

Comparative immunochemical analysis of intraspecies distinctions of serum proteins of starred sturgeon <Emphasis Type="Italic">Acipenser stellatus</Emphasis> (Acipenseriformes,Acipenseridae) from the Caspian basin

By methods of immunochemical analysis, antigenic characteristics of serum proteins of starred sturgeon Acipenser stellatus migrating to the Volga, the Ural, and the Kura are studied. Antigens of serum proteins of starred sturgeon with normal homo- and heteroantisera are differentiated immunoelectochemically into 22–25 components. Cross absorption of antisera revealed the presence of specific antigens. Volga starred sturgeon differs from the Ural starred sturgeon in one antigen which belongs to α₂-globulins and differs from the Kura starred sturgeon in two antigens which manifest themselves in the zone of β₁-globulins. Kura starred sturgeon differs from the Ural starred sturgeon in two antigens which are in the zone of α₂-globilins. It is concluded that presence of specific antigens in the Volga and the Kura population of starred sturgeon and in their absence in the Ural starred sturgeon indicate the reproductive independence of these intraspecies groups.