Factors influencing the natural reproduction decline in the beluga (Huso huso,Linnaeus, 1758), Russian sturgeon (Acipenser gueldenstaedtii,Brandt & Ratzeburg, 1833), and stellate sturgeon (A. stellatus,Pallas, 1771) of the Volga–Caspian basin: A review

The review describes the changes in natural reproduction of three important sturgeon species in the Volga–Caspian basin: (a) the beluga (Huso huso Linneaus, 1758), (b) the Russian sturgeon (Acipenser gueldenstaedtii Brandt &Ratzeburg, 1833), and (c) the stellate sturgeon (Acipenser stellatus Pallas, 1771). Since the past 60 years, these species responded to severe influences of natural and anthropogenic factors. On the basis of original and published data, an analysis has been made of (a) the numbers of larvae migrating from spawning sites (according to plankton net survey), (b) fecundity and histological anomalies in gonad development, (c) the numbers of adult sturgeons in the Caspian Sea and of spawners migrating to the Volga River (according to trawl and beach seine survey), and (d) foraging resources for the sturgeons. The results show that their natural reproduction in the Volga–Caspian basin has declined drastically during the past decades under the impact of (a) fluctuations of the Caspian Sea level and flow discharge from the Volga River, (b) blockage of sturgeon migration routes and loss of spawning sites because of dam construction, (c) water pollution in the lower reaches of the Volga River and in the Caspian Sea, and (d) intensive and selective illegal and unreported fishing. The relative significance of these factors has been changing during the study period.     

Mitochondrial genome of the Siberian sturgeon Acipenser baerii

The complete mitochondrial genome of Siberian sturgeon Acipenser baerii had been determined. The total length of the mitogenome was 16,763?bp and had 13 protein-coding, 22 tRNA, and 2 rRNA genes. Except for the eight tRNA and Nd6 genes, all other mitochondrial genes are encoded on the heavy strand. The overall base composition of the heavy strand is 30.3% A, 24.3% T, 29.1% C, 16.3% G, with an AT content of 54.6%. The DNA sequence of A. baerii shared 97.8, 97.6, 93.5, 91.6, 93.6, and 87.1% sequence homology with that of Acipenser sinensis, Acipenser gueldenstaedtii, Acipenser transmontanus, Acipenser dabryanus, Acipenser stellatus, and Polyodon spathula. Molecular data presented here provide a useful tool for evolutionary as well as population genetics studied.     

Development of sturgeon catches in German and adjacent waters since 1980

The data of sturgeon catches in German and adjacent waters since 1980 have been collected from the major river systems and coastal waters in Germany and neighbouring countries. Over the past 10 years records on catches of exotic sturgeon species increasingly occur in the commercial and recreational fisheries, including the following species: Acipenser baerii, A. gueldenstaedtii as well as hybrids from different parental species such as H. huso x A. ruthenus, A. baerii x A. ruthenus. A total of 227 records are reported, including data on their distribution. Accidental or deliberate introductions of sturgeons have been mediated by aquaculture and/or petfish-industries. Their occurrence is discussed in relation to plans for the re-establishing of the native A. sturio.     

Present status of commercial stocks of sturgeons in the Caspian Sea basin

Catches for the last 25 years are analyzed for beluga Huso huso, stellate sturgeon A. stellatus and Russian sturgeon Acipenser gueldenstaedtii, which are the three commercially important species of sturgeons found in the Caspian Sea Basin. Population sizes for generations born between 1961 and 1970 are estimated, and found to depend on natural reproduction and the number of young fish stocked annually from sturgeon hatcheries located in the Volga River Delta. A ban on sea fishing from 1962 to 1991 positively impacted the number and total biomass of commercial stocks. Sturgeon growth rates depend on water levels in the Caspian Sea. In order to preserve Caspian Sea sturgeon populations, it will be necessary to coordinate efforts of all countries surrounding the Caspian Sea to achieve rational harvests, preserve juveniles, and produce at least 100 million juveniles annually from hatcheries.     

Juvenile growth of Acipenser ruthenus and 4 different sturgeon hybrids

Juvenile growth of A. ruthenus and four different sturgeon hybrids ( Huso huso x A. ruthenus, A. baerii x A. ruthenus, A. gueldenstaedtii x A. ruthenus, A. gueldenstaedtii x H. huso ) was studied for 71 days applying two feeding regimes, offering a fry diet (3.5 % daily rate) for 26 days for the hybrids and 41 days for A. ruthenus and a fattening diet (3 % daily rate) for 45 days and 30 days respectively. Significant growth differences occured at the end of experiment: The hybrid A. gueldenstaedtii x H. huso showed the highest, A. ruthenus the lowest growth.     

High‐throughput SNP‐genotyping analysis of the relationships among Ponto‐Caspian sturgeon species

Legally certified sturgeon fisheries require population protection and conservation methods, including DNA tests to identify the source of valuable sturgeon roe. However, the available genetic data are insufficient to distinguish between different sturgeon populations, and are even unable to distinguish between some species. We performed high‐throughput single‐nucleotide polymorphism (SNP)‐genotyping analysis on different populations of Russian (Acipenser gueldenstaedtii), Persian (A. persicus), and Siberian (A. baerii) sturgeon species from the Caspian Sea region (Volga and Ural Rivers), the Azov Sea, and two Siberian rivers. We found that Russian sturgeons from the Volga and Ural Rivers were essentially indistinguishable, but they differed from Russian sturgeons in the Azov Sea, and from Persian and Siberian sturgeons. We identified eight SNPs that were sufficient to distinguish these sturgeon populations with 80% confidence, and allowed the development of markers to distinguish sturgeon species. Finally, on the basis of our SNP data, we propose that the A. baerii‐like mitochondrial DNA found in some Russian sturgeons from the Caspian Sea arose via an introgression event during the Pleistocene glaciation.     

Molecular analysis of phylogeographic subspecies in three Ponto-Caspian sturgeon species

Sturgeons (Order Acipenseriformes) represent an extremely valuable natural resource that is now facing depletion. In the current study we evaluate if the traditional classification in subspecies of Acipenser gueldenstaedtii, Acipenser stellatus and Huso huso, endemic to Ponto-Caspian region is sustained by molecular analysis and if these represent Evolutionary Significant Units (ESUs) that should be managed separately in conservation programs. To examine the classification of taxonomic entities we sequenced a fragment of the mitochondrial control region in case of three sturgeon species that inhabit the North-western of Black Sea and migrate for reproduction in the Lower Danube. Beside these sequences, we used previously published sequences from sturgeon individuals sampled in the Black Sea, Azov Sea and Caspian Sea. We determined the genetic diversity and genetic differentiation, conducted a Population Aggregation Analysis (PAA) and inferred an intraspecific molecular phylogeny and haplotype network. The results indicated a low level of genetic differentiation between the geographically designated subspecies and did not support a significant divergence or reciprocal monophyly between them. Our results confirm previous genetic studies with smaller samples sizes, but additional analyses including nuclear markers should be conducted for proper recommendations aiming at the development of conservation programs.     

Development of the skull and pectoral girdle in Siberian sturgeon,Acipenser baerii,and Russian sturgeon,Acipenser gueldenstaedtii (Acipenseriformes: Acipenseridae)

The head is considered the major novelty of the vertebrates and directly linked to their evolutionary success. Its form and development as well as its function, for example in feeding, is of major interest for evolutionary biologists. In this study, we describe the skeletal development of the cranium and pectoral girdle in Siberian (Acipenser baerii ) and Russian sturgeon (A. gueldenstaedtii ), two species that are commonly farmed in aquaculture and increasingly important in developmental studies. This study comprises the development of the neuro‐, viscero‐ and dermatocranium and the dermal and chondral components of the pectoral girdle, from first condensation of chondrocytes in prehatchlings to the early juvenile stage and reveals a clear pattern in formation. The otic capsules, the parachordal cartilages, and the trabeculae cranii are the first centers of chondrification, at 8.4mm TL. These are followed by the mandibular, then the hyoid, and later the branchial arches. Teeth form early on the dentary, dermopalatine, and palatopterygoid, and then appear later in the buccal cavity as dorsal and ventral toothplates. With ongoing chondrification in the neurocranium a capsule around the brain and a strong rostrum are formed. Dermal ossifications start to form before closure of the dorsal neurocranial fenestrae. Perichondral ossification of cartilage bones occurs much later in ontogeny. Our results contribute data bearing on the homology of elements such as the lateral rostral canal bone that we regard homologous to the antorbital of other actinopterygians based on its sequence of formation, position and form. We further raise doubts on the homology of the posterior ceratobranchial among Actinopteri based on the formation of the hyoid arch elements. We also investigate the basibranchials and the closely associated unidentified gill‐arch elements and show that they are not homologous. J. Morphol. 278:418–442, 2017. © 2017 Wiley Periodicals, Inc.     

Existence of transferrin polymorphism in a species of sturgeon from the Caspian Sea: Acipenser stellatus

Though various subdivisions have been proposed in literature for species of sturgeon from the Caspian Sea, these subdivisions still remain hypothetical. Research on the erythrocyte antigens of four species of anadrome sturgeons, caught off the Iranian coast has not evidenced any erythrocyte antigenic differentiations among these four species. After marking serum with 59Fe, doing paper and starch electrophoreses and revealing the marked serum proteins by autoradiography, we have shown that a transferrin polymorphism exists in Acipenser stellatus. This isotopic marking also enabled us to identify by starch electrophoresis marked proteins corresponding to transferrins in the serum of three other species of sturgeon: Acipenser guldenstadti, Acipenser nudiventris and Huso huso. It has not however been possible to determine with certainty the existence of a transferrin polymorphism in these three species.     

Intraspecific genetic polymorphism of Russian sturgeon <Emphasis Type="Italic">Acipenser gueldenstaedtii</Emphasis>

Three populations (Azov, Caspian, and Black Sea) of Russian sturgeon Acipenser queldenstaedtii were tested for polymorphism at nuclear (RAPD and microsatellites) and mitochondrial (PCR identification of two mitotypes) markers. In addition, morphometric analysis of he representatives of Azov population was carried out. According to the morphological characters, the Black Sea population occupied an intermediate position between the Caspian and Azov populations, reflecting the phylogeography of this species. In agreement with the morphometric data, genetic distances (the data of STR analysis) also placed the Black Sea population between the Caspian and Azov populations (F _ST = 0.058 and 0.043). The genetic distance between the Azov and Caspian population was somewhat higher (F _ST = 0.070). The highest allelic polymorphism at four microsatellite loci was found observed in Caspian population, while the lowest polymorphism was in the Sea of Azov. RAPD analysis distinguished high polymorphism within the populations, although it was not feasible for interpopulation analysis. Using the method differentiating the “baerii-like” and typical “gueldenstaedtii” mitotypes, the absence of the “baerii-like” marker in the Black Sea population was demonstrated. The frequency of this marker in Caspian and Azov populations constituted 31.1 and 1.8%, respectively. Possible evolutionary reasons for the interpopulation differences observed are discussed.     

不同开口饵料对西伯利亚鲟仔鱼生长、存活和体成分的影响

分别采用水丝蚓（Limnodrilus sp.）、卤虫无节幼体（Artemia nauplii）、枝角类（Moina sp.）和人工饲料饲养西伯利亚鲟仔鱼30 d,研究不同开口饵料对西伯利亚鲟仔鱼生长、存活率和体成分的影响.结果表明：卤虫无节幼体为西伯利亚鲟最适开口饵料,仔鱼的存活率最高（96.67%）; 投喂水丝蚓组生长速度最快;而人工饲料组生长速度明显低于其他组,且成活率最低.不同开口饵料组间仔鱼体成分差异显著,人工饲料组水分含量最高,且粗蛋白和粗灰分含量最低.采用卤虫无节幼体为西伯利亚鲟仔鱼开口饵料,然后采用水丝蚓进行强化培育,能获得较好的生长速度和存活率.     

Morphology and systematic significance of sclerolepidia in the weevils (Coleoptera: Curculionoidea)

The Russian sturgeon, Acipenser gueldenstaedtii, is closely related to three other sturgeon species (A persicus, A. naccarii and A baerii), with populations in the Caspian Sea containing a cryptic lineage with an A. baerii‐like mtDNA profile. Using morphological evidence (morphometrics, meristics) and additional genetic analysis (cytochrome b gene and control region sequencing), cryptic lineages within the Russian sturgeon and their relation to other closely related species of sturgeons are further examined. These data indicate that three genetic forms exist within what is presently known as A. gueldenstaedtii. These forms include the pure A. gueldenstaedtii and A. baerii‐like individuals plus a third rare genetic form whose mtDNA is similar to the mtDNA of the Adriatic sturgeon, A. naccarii. Morphological comparison of the three forms and the Yenisei River A baerii indicates that although the three forms of A. gueldenstaedtii are not different from one another, all three significantly differ from the Yenisei River A. baerii. Competing explanations, including translocation and centre of origin hypotheses are considered. The three geneticforms of A. gueldenstaedtii likely colonized different geographic areas during different geological periods, and subsequently evolved in these regions independently into the species currently recognized as A. gueldenstaedtii, A. naccarii and A. baerii.     

Diet composition of the Persian sturgeon <Emphasis Type="Italic">Acipenser persicus</Emphasis> at the coast of the Guilan Province,Caspian Sea

Sturgeons are one of the most important and valuable species in the Caspian Sea. This investigation (2000–2002) was aimed at determining the feeding habits and the main and secondary prey organisms consumed by the Persian sturgeon (Acipenser persicus Borodin, 1897) living at depths less than 10 m in the Caspian Sea (Guilan Province). The food spectrum of immature A. persicus was comprised of benthic invertebrates of seven genera and fishes of three genera. The main prey items of immature A. persicus were polychaete worms and the secondary prey were crustaceans. The study of stomach contents showed that polychaetes were the most important component of the diet of immature A. persicus of the length class up to 25 cm.     

Contemporary status of Caspian sturgeon (Acipenseridae) stock and its conservation

The paper describes the contemporary status of sturgeon stocks in the Caspian Sea. The effect of natural reproduction and hatchery production on sturgeon population restocking is estimated. Variations in the status of spawning populations of sturgeons migrating into the Volga River were analysed. Recommendations on appropriate measures for conservation of the Caspian sturgeon stocks are presented.     

Historic speciation and recent colonization of Eurasian monkey gobies (Neogobius fluviatilis and N. pallasi) revealed by DNA sequences,microsatellites, and morphology

Aim Hidden diversity within an invasive ‘species’ can mask both invasion pathways and confound management goals. We assessed taxonomic status and population structure of the monkey goby Neogobius fluviatilis across Eurasia, comparing genetic variation across its native and invasive ranges. Location Native populations were analysed within the Black and Caspian Sea basins, including major river drainages (Dnieper, Dniester, Danube, Don and Volga rivers), along with introduced locations within the upper Danube and Vistula river systems. Methods DNA sequences and 10 nuclear microsatellite loci were analysed to test genetic diversity and divergence patterns of native and introduced populations; phylogenetic analysis of mtDNA cytochrome b and nuclear RAG‐1 sequences assessed taxonomic status of Black and Caspian Sea lineages. Multivariate analysis of morphology was used to corroborate phylogenetic patterns. Population genetic structure within each basin was evaluated with mtDNA and microsatellite data using F_ST analogues and Bayesian assignment tests. Results Phylogenetic analysis of mitochondrial and nuclear sequences discerned a pronounced genetic break between monkey gobies in the Black and Caspian Seas, indicating a long‐term species‐level separation dating to c. 3 million years. This pronounced separation further was confirmed from morphological and population genetic divergence. Bayesian inference showed congruent patterns of population structure within the Black Sea basin. Introduced populations in the Danube and Vistula River basins traced to north‐west Black Sea origins, a genetic expansion pattern matching that of other introduced Ponto‐Caspian gobiids. Main conclusions Both genetic and morphological data strongly supported two species of monkey gobies that were formerly identified as subspecies: N. fluviatilis in the Black Sea basin, Don and Volga Rivers, and the Kumo‐Manych Depression, and Neogobius pallasi in the Caspian Sea and Volga River delta. Genetic origins of introduced N. fluviatilis populations indicated a common invasion pathway shared with other introduced Ponto‐Caspian fishes and invertebrates.     

Species structure, contemporary distribution and status of the Siberian surgeon Acipenser baerii

A detailed analysis of the historical and contemporary range of the Siberian sturgeon, Acipenser baerii, shows that the contemporary status of its populations and forms can be described as threatened or endangered. Recently, the abundance of the nominal subspecies, A. b. baerii, which inhabits mainly the Ob River basin, decreased sharply. Due to construction of hydroelectric dams, up to 40% of the spawning grounds became inaccessible for migrating sturgeon of this subspecies. The Lake Baikal subspecies, A. baerii baicalensis, is extremely rare and was included in the Russian Federation Red Data Book in 1983. The abundance of the east Siberian subspecies, A. baerii stenorrhynchus, inhabiting the basins of the east Siberia rivers, has also significantly decreased during the last few years. Its range in the Yenisey and Lena River basins is gradually being reduced. Gametogenesis is anomalous in a high number of females from all populations of this subspecies (in the Kolyma and Indigirka river stocks 80–100% of females were anomalous in 1987–1989). These anomalies seem to be caused by high levels of water pollution.     

Application of microsatellite markers for genetic conservation and management of Persian sturgeon (Acipenser persicus,Borodin, 1897) in the Caspian Sea

A study was conducted to ascertain the genetic structure and the level of heterozygosity of Acipenser persicus in the Caspian Sea. A total of 167 fish were randomly collected from Turkmenistan, Russia and two regions of Iran. The number of alleles of eleven microsatellite markers ranged from 3 to 21 and the mean observed values of heterozygosity were 0.56 ± 0.20, 0.64 ± 0.14, 0.67 ± 0.16, and 0.64 ± 0.11. The observed heterozygosity was lower than the expected levels. The observed low genetic differentiation indicates that all populations are closely related. Hence, inbreeding is a potential problem, which should be taken into consideration in future breeding programs to avoid a further decline in genetic diversity.     

The state of natural reproduction of stellate sturgeon Acipenser stellatus in the Lower Volga

Data obtained during 1979–2005 on the natural reproduction of stellate sturgeon Acipenser stellatus and water level in the Volga River were analyzed. The relationship between the number of stellate sturgeon larvae migrating down the river, flow quantity during the summer period of low water and the number of spawners entering spawning grounds was shown. Fish productivity of spawning grounds located in the river channel in different zones of the Lower Volga was estimated. Recommendations are presented concerning the increase in the level of stellate sturgeon natural reproduction in the lower pool of the Volgograd hydrosystem.     

Comparative evaluation of sturgeon larvae and juveniles reared under control of seasonal propogation of the wild and domestic breeders

Sturgeon populations ( Acipenser gueldenstaedtii and A. stellatus ) in the Sea of Azov basin are maintained largely through stock enhancement. A monitoring is in operation for biological characteristics of juveniles, including body length and mass, physiological‐biochemical indices, teratology, thermal stability, salt resistance, oxygen deficiency resistance and melanophore adaptive response as indicators of physiological fitness, and neuro‐pharmacological testing with a sedative (MS‐222). Behavioural experiments include the assessment of background movement and reactivity to the effect of low/high frequency sounds and light of long/short duration. Juveniles obtained from breeders in which the reproductive cycle had been delayed for up to 90 days did not show significantly different levels of morphological anomalies compared to juveniles obtained with conventional reproductive techniques. The most frequent defects are observed in pectoral fins (up to 20 per cent) and olfactory organs (up to 10 per cent). Fingerlings showed and adequate and timely adaptive reaction of melanophores towards dark and light background. The experiment demonstrated that sturgeon fingerlings produced under controlled conditions are euryhaline and robust to thermal and oxygen stress. Some differences in biological attributes were noted between juveniles obtained from wild and domesticated breeders of A. gueldenstaedtii and A. stellatus .     

Dispermic androgenesis in sturgeons with the help of cryopreserved sperm: production of androgenetic hybrids between Siberian and Russian sturgeons

Dispermic androgenesis was used to produce, for the first time, an androgenetic progeny of the Siberian sturgeon (Acipenser baerii) and the androgenetic nuclear cytoplasmic hybrids (Siberian sturgeon, A. baerii x Russian sturgeon, A. gueldenstaedtii) using cryopreserved sperm. Microsatellite DNA analysis confirmed exclusively paternal inheritance in the androgenetic progeny of Siberian sturgeon. Heterozygotes for certain microsatellite loci were detected among the androgenetic hybrids, thereby confirming a dispermic nature of androgenesis. According to the data of comparative morphological analysis, the obtained androgenetic hybrid, by the age of 15 months old, was completely identical to the paternal species. Both a female and a male were detected in the androgenetic sturgeon progenies, which is of interest for producing bisexual progenies via androgenesis. The data of this study confirm the feasibility of dispermic androgenesis using cryopreserved sperm to preserve and recover the gene pools of endangered sturgeon species.