Formation and structure of egg envelopes in Russian sturgeon Acipenser gueldenstaedtii (Acipenseriformes: Acipenseridae)

The covering of the eggs in Russian sturgeon Acipenser gueldenstaedtii consists of three envelopes (the vitelline envelope, chorion and extrachorion) and is equipped with multiple micropyles. The most proximal to the oocyte is the vitelline envelope that consists of four layers of filamentous and trabecular material. The structural components of this envelope are synthesized by the oocyte (primary envelope). The chorion encloses the vitelline envelope. The extrachorion covers the external surface of the egg. Examination of the arrangement of layers that comprise the egg envelopes together with the ultrastructure of follicular cells revealed that the chorion and extrachorion are secondary envelopes. They are secreted by follicular cells and are built of homogeneous material. During formation of egg envelopes, the follicular cells gradually diversify into three morphologically different populations: 1) cells covering the animal oocyte region (cuboid), (2) main body cells (cylindrical) and (3) micropylar cells. The apical surfaces of follicular cells from the first two populations form processes that remain connected with the oocyte plasma membrane by means of gap junctions. Micropylar cells are located at the animal region of the oocyte. Their apical parts bear projections that form a barrier to the deposition of materials for egg envelopes, resulting in the formation of the micropylar canal.     

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.     

Morphological peculiarities of pronephros in Russian sturgeon, Acipenser gueldenstaedtii Brandt (order acipenseriformes, family acipenseridae)

The structure of the pronephros in Russian sturgeon larvae, Acipenser gueldenstaedtii Brandt, at different stages of early postembryonic development (from hatching till 14 days old), was studied with histological and electron microscopy methods. The formed pronephros is represented by a system of bilaterally located pronephric tubules and an external single glomus, which is not integrated directly into pronephric tubules and is located in closed pronephric chamber. The glomus is positioned below the dorsal aorta and is vascularized by its capillaries. The thin structure of the glomus has the same characteristic features that are typical of and needed for the functions of any filtering organ. By the time when larvae transfer fully to exogenous feeding, the pronephros undergoes significant degradation and it is replaced by the mesonephric kidney which develops during the period of function of the pronephros. The peculiarities of the pronephros in acipenserids are discussed comparatively with the same organ in teleosts and amphibians.     

A biometric method for determining the sex of acipenserids, including the Russian sturgeon Acipenser gueldenstaedtii (Acipenseridae) of the Azov Population

With reference to the Russian sturgeon Acipenser gueldenstaedtii of the Azov Population, it is demonstrated that the sex of acipenserids may be determined biometrically. A measurement scheme of the head is suggested, which gives the possibility to determine gender in live sturgeons. A discriminate equation is composed for the identification of the sex of individuals of the Russian sturgeon in a sufficiently wide size-age range, irrespective of the maturity stage of the gonads.     

The skull of the Chinese sturgeon,Acipenser sinensis (Acipenseridae)

The Chinese sturgeon, Acipenser sinensis, is a large member of Acipenseridae now found only in the Yangtze River and the Yellow and East China seas. The goal of this paper was to describe the skull of A. sinensis in the context of recent anatomical and systematic studies of sturgeons. Five specimens (354–670 mm standard length) were prepared as skeletons. The left and right parietals and frontals are broadly separated by a median fontanelle. The lateral‐most lateral extrascapular variably supports the confluence of the supratemporal, occipital and trunk lateral lines. There is no distinct ventral supraorbital process as found in other sturgeons. The anterodorsal portion of the snout is unique among Acipenseridae by having a single large anamestic dorsal rostral bone instead of a series of separate dorsal rostral bones. There are 0–2 lateral rostral bones on each side positioned anterior to but not in contact with the horizontal arm of the jugal. The dorsal surface of the neurocranium lacks a pineal opening, and its anterior tip is sharply pointed in the smaller specimens examined and gently curved in larger specimens. The anteromedial arm of the palatopterygoid is broad relative to other acipenserids. These new morphological data are discussed and compared among Acipenseridae.     

Development of the muscles associated with the mandibular and hyoid arches in the Siberian sturgeon,Acipenser baerii (Acipenseriformes: Acipenseridae)

The skeleton of the jaws and neurocranium of sturgeons (Acipenseridae) are connected only through the hyoid arch. This arrangement allows considerable protrusion and retraction of the jaws and is highly specialized among ray‐finned fishes (Actinopterygii). To better understand the unique morphology and the evolution of the jaw apparatus in Acipenseridae, we investigated the development of the muscles of the mandibular and hyoid arches of the Siberian sturgeon, Acipenser baerii. We used a combination of antibody staining and formalin‐induced fluorescence of tissues imaged with confocal microscopy and subsequent three‐dimensional reconstruction. These data were analyzed to address the identity of previously controversial and newly discovered muscle portions. Our results indicate that the anlagen of the muscles in A. baerii develop similarly to those of other actinopterygians, although they differ by not differentiating into distinct muscles. This is exemplified by the subpartitioning of the m. adductor mandibulae as well as the massive m. protractor hyomandibulae, for which we found a previously undescribed portion in each. The importance of paedomorphosis for the evolution of Acipenseriformes has been discussed before and our results indicate that the muscles of the mandibular and the hyoid may be another example for heterochronic evolution.     

Growth performance of juvenile Russian sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) at two stocking densities in net cages

The growth performance of juvenile sturgeon (Acipenser gueldenstaedtii Brandt & Ratzenburg, 1833) was studied in experimental net cages (2 m × 2 m × 2 m) in freshwater Sapanca Lake. Fertilized eggs were imported from Krasnodar, Russia in January 2001. Two experimental stocking densities were employed (12 and 8 ind. m⁻³). Sturgeon were hand‐fed a pelleted commercial trout feed twice daily throughout the 203‐day experiment period. Fish were grown at ambient temperature (12.7–28.5°C) and natural photoperiod. Initial and final mean body weights were 279.5 g (±31.27) and 1112.8 g (±234.77) in the first group, and 271.1 g (±28.21) and 1140.5 g (±213.31) in the second group, respectively. Results were a fourfold biomass density increase in both trials from an initial 3.48 to 12.4 kg m⁻³ (high density) and 2.2 to 8.8 kg m⁻³ (low density). Mean specific growth rate (SGR) was determined as 2.69% day⁻¹ in both groups. Mean condition factor (CF) at the end of the experiment was 0.36 ± 0.05 in the high‐density group and 0.41 ± 0.05 in the low‐density group. Mean feed conversion ratio (FCR) was calculated to be 5.7 and 5.8, respectively. Survival was 92.7% in the first group (high density) and 96.1% in the second group (low density). The results demonstrated that sturgeon juveniles can be raised in cages and that growth performance (CF, SGR and FCR) and mortality of sturgeon were not significantly different at the two stocking densities (P > 0.05) tested.     

Evidence of mitochondrial DNA clones of Siberian sturgeon, Acipenser baerii, within Russian sturgeon, Acipenser gueldenstaedtii, caught in the River Volga

Eleven of 34 sturgeons caught in the River Volga classified morphologically as Acipenser gueldenstaedtii were identified as Acipenser baerii from sequence analysis of the mitochondrial cytochrome- b gene. The Caspian Sea and its tributaries including the Volga are not native habitats of A. baerii . No A. baerii haplotype was observed in A. gueldenstaedtii from the Sea of Azov or the South Caspian Sea. Genetic contamination of A. gueldenstaedtii with A. baerii or A. baerii hybrids has occurred in the Volga. Crosses and backcrosses of these specimens with native A. gueldenstaedtii resulted in the loss of the morphological diagnostic A. baerii features. These findings are of special concern for conservation and management programmes, as well as for specimen identification for caviar trading control.     

中国鲟科一新记录种——小体鲟

在中国,小体鲟(Acipenser ruthenus)被认为自然分布于额尔齐斯河,但至今尚无发现该种的文献报道,在额尔齐斯河是否确有分布还存疑问。2019年9月,在中国额尔斯斯河下游(185团)采集到鲟类标本1尾,全长91.5 cm,体重5 520 g。标本背骨板11,侧骨板64,腹骨板12;口腹位,较小,口下唇中间断裂;鳃耙数17,符合小体鲟的形态特征。利用线粒体DNA Cyt b基因序列(1 141 bp),对鲟属10个物种的亲缘关系及系统发育进行分析,该种与分布于鄂毕河、多瑙河的小体鲟遗传距离最近(序列分歧为0～0.000 2),并在进化树中聚为一支,应属于种内关系。基于以上研究结果,可以确定该标本即为小体鲟,在额尔齐斯河首次被发现,为中国鲟科分布新记录种,标本保存于中国水产科学研究院黑龙江水产研究所鱼类标本馆(标本号80092871)。     

Regulation of spermatozoa motility in response to cations in Russian sturgeon Acipenser gueldenstaedtii

The aim of this study was to investigate the response of Russian sturgeon (Acipenser gueldenstaedtii) sperm to external cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) and their susceptibility on the induction of motility and swimming behavior. An in vitro spermatozoa motility assay was used by a computer-aided Motion-Analysis system. Sperm motility was inhibited by 60 mm NaCl (∼140 mOsm/kg) and 0.7 mm KCl solutions (∼ 21.4 mOsm/kg). The Ca²⁺ and Mg²⁺ ions were not able to inhibit spermatozoa motility. By contrast, Na⁺ within a limited concentration range (between 45 and 55 mm) was able to reverse the inhibitory effect of K⁺ at the critical concentration (0.7 mm). Ca²⁺ and Mg²⁺ were also able to reverse the K⁺-mediated spermatozoa motility restriction at concentrations starting at 0.01 and 0.1 mm, respectively. These results provide evidence for the role of K⁺ in suppressing spermatozoa motility, and suggest that Ca²⁺, Mg²⁺, and possibly Na⁺ trigger motility in Russian sturgeon sperm.     

Gastric evacuation in endangered Russian sturgeon (Acipenser gueldenstaedtii): Effects of body and meal sizes

This study aimed to parameterize the effects of body and meal sizes on the gastric evacuation (GE) of farmed Russian sturgeon (Acipenser gueldenstaedtii) fed on live food (whiting fish) or commercial pellets. The radiography technique was used to monitor the evacuation of food from the stomach into the intestine at postprandial time. Acipenser gueldenstaedtii of different body sizes (total length ranged 82–105 cm) were fed on meal sizes ranged from 23 to 72 g composed of either live food or commercial pellets (had a 20% of BaSO₄ as a radiopaque material). The square root model was found to adequality describe the process of GE in A. gueldenstaedtii independently of meal type and size. The effects of fish size on GER was described by simple power model and can be summarized by , where ρ_L was 0.000053 for live food and 0.000062 for commercial pellets (estimated from combined GE data), S_t is stomach contents (g), L is fish total length (cm) and t is time (h). The results of this study will provide a useful tool to estimate the stomach fullness of A. gueldenstaedtii at postprandial time t. Such information should assess the feeding strategy to minimize feed wastage and optimize the fish growth.     

Polyphyly of mtDNA lineages in the Russian sturgeon, Acipenser gueldenstaedtii: forensic and evolutionary implications

Molecular species identification methods are an important component of CITES monitoring programs for trade in sturgeon and caviar. To date, obtaining molecular evidence for distinguishing caviar from four closely related Eurasian sturgeon species Acipenser baerii (Siberian sturgeon), A. gueldenstaedtii (osetra), A. persicus (Persian sturgeon), A. naccarii (Italian sturgeon) remains problematic. Using approximately 2.3 kb of mtDNA sequence data (cytochrome b, NADH5, control region), we find this to be attributable to the polyphyletic nature of these mitochondrial DNA markers in the Russian sturgeon, A. gueldenstaedtii. Two mitochondrial lineages are present within this species: one is phylogenetically affiliated with A. persicus and A. naccarii, while the other clusters with A. baerii. These findings have a direct impact on molecular testing of commercial caviar and demonstrate the necessity of using large sample sizes when constructing forensic databases. Furthermore, the results affect current taxonomic designations for these species as well as hypotheses concerning their evolutionary origins.     

Hypervariability of the D-loop region in mitochondrial DNA of Russian sturgeon <Emphasis Type="Italic">Acipenser gueldenstaedtii</Emphasis> (Acipenseriformes,Acipenseridae)

The structure of the D-loop region in mitochondrial DNA (mtDNA) of Russian sturgeon Acipenser gueldenstaedtii from the Azov Sea population was studied with the method of direct sequencing. Interindividual heteroplasmy of the length of mtDNA in the region of D-loop realized by the presence of a different number of tandem repeats (82 pairs of bases) was found. Analysis of tandem repeats in the D-loop region in mtDNA in the studied sample (28 individuals) revealed eight mitotypes differed in the pattern of nucleotide substitution and in the number of tandem repeats (2, 3, and 4 repeats). Revealed mitotypes can be considered as potential genetic markers for different biological groups, schools, or seasonal races of A. gueldenstaedtii.     

Myotomal myogenesis of axial muscle in the sturgeon Acipenser baeri (Chondrostei, Acipenseriformes)

Compared to teleost fishes, a unique character of the myogenesis of the plesiomorphic A. baeri is the fusion of myoblasts derived from the somite, leading to the formation of multinucleate muscle lamellae. Then, the lamellae are converted into cylindrical muscle fibres. The mechanism of transformation of lamellae into fibres is still debatable. Early embryonic muscle growth is mainly due to the hypertrophy of somite-cell derived stock. After hatching, hypertrophic growth occurs parallel to hyperplastic growth. Proliferatively active mesenchymal cells, which migrate from the intermyotomal space into the myotomes, participate in both processes.     

俄罗斯鲟仔鱼初次摄食时间对生长及存活的影响

以人工繁育的俄罗斯鲟仔鱼为对象,采用实验生态学方法,研究了初次摄食时间对生长及存活的影响。结果表明：在水温17.4 ℃下,仔鱼在9～10日龄初次摄食,初次摄食前投喂对俄罗斯鲟仔鱼的生长和存活无显著性影响,延迟2 d以上初次摄食对生长影响明显,存活率在18日龄初次摄食时显著下降,24日龄时饥饿仔鱼全部死亡;23～24日龄时仔鱼如不能建立外源营养即达到饥饿不可逆点（PNR）。人工养殖条件下,俄罗斯鲟仔鱼必须在初次摄食后14 d内建立起主动摄食能力才能保证其仔鱼的正常发育、生长和存活。     

Comparative coelomic fluid composition of sterlet sturgeon Acipenser ruthenus Linnaeus, 1758, Siberian sturgeon Acipenser baerii Brandt, 1869, and Russian sturgeon Acipenser gueldenstaedtii Brandt & Ratzeburg, 1833

The objectives of this study were to compare the physicochemical properties of coelomic fluid (CF) in three sturgeon species, sterlet sturgeon Acipenser ruthenus (age 5–8 years), Siberian sturgeon Acipenser baerii (age 15–20 years), and Russian sturgeon Acipenser gueldenstaedtii (age 13–18 years). For the study, CF was collected by plastic pipette from the eggs of mature female sterlet sturgeon (N = 10), Siberian sturgeon (N = 7) and Russian sturgeon (N = 4); osmolality, pH, ionic composition (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?), glucose, cholesterol and total protein of the CF were then analyzed. Mean concentration of K⁺ (4.4–6.11 mmol/L), Cl^? (89.8–98.0 mmol/L), Ca²⁺ (0.87–0.96 mmol/L), Mg²⁺ (0.57–0.67 mmol/L), cholesterol (0.13–0.16 mmol/L), total protein (2.41–3.57 g/L), pH (7.92–7.98), and osmolality (190–213 mOsm/kg) of CF were not significantly different among these three species. However, the mean concentration of Na⁺ was significantly lower in sterlet sturgeon (104.6 ± 7.7 mmol/L; p < .05) than in the Siberian (126.4 ± 6.2) and Russian (123.0 ± 5.9) sturgeon. For these three species, Na⁺, K⁺, Cl^?, and Mg²⁺ were the dominating ions; several significant correlations were observed among these ions and other physiochemical properties of CF. This is the first report on the ionic and biochemical composition of the CF of sterlet, Siberian and Russian sturgeon, which can be used as a reference point for further development of artificial media for the short‐term storage of unfertilized sturgeon eggs as well as for the standardization of the fertilization protocol for these species in controlled reproduction.