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.     

Biological peculiarities of the industrially bred juvenile Russian sturgeon Acipenser gueldenstaedtii (Acipenseridae, Acipenseriformes) in the Don

We discuss results of the investigation into biological peculiarities of the juvenile Russian sturgeon (Acipenser gueldenstaedtii) from the Aksay-Don Sturgeon Hatchery living in a natural riverine environment and migrating seaward. We supply data on the growth rate, geographic distribution, behavior and the feeding manner of the juvenile Russian sturgeon in the Don. We have estimated the survival rate of the industrially bred juvenile Russian sturgeon living in a natural environment. Apart from the nutritive base in the river and the predation pressure, we found that ecologically and physiologically determined biological characteristics mostly influence the survival rate in the juvenile Russian sturgeon released into the Don. The findings allow estimation of artificial propagation of the Russian sturgeon in the Azov Sea basin.     

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.     

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.     

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.     

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.     

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.     

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.     

Features of osmotic and ionic regulations in Russian sturgeon (Acipenser güldenst?dti Brandt)

The osmolality of blood serum of one group of Russian sturgeon fished out in Southern Caspian Sea was the same as their habitat, the other group of sturgeons had a serum osmolality several per cent lower than that of sea-water in this part of the Caspian Sea. Ion concentrations in blood serum in sturgens were similar in fresh water and the Caspian Sea. The feature of the Russian sturgeon's kidney is intensive potassium secretion and a comparatively low level of magnesium secretion.     

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。     

Behavioural responses to various chemical incentives in hybrid beluga x Russian sturgeon (Huso huso x Acipenser gueldenstaedtii) fry

Behavioural contact feeding responses to various chemical incentives were studied in hybrid beluga x Russian sturgeon ( Huso huso x Acipenser gueldenstaedtii ) fry. Solutions of 29 amino-acids (10–2 M); aqueous extracts of various vegetable, animal and microbiological components of commercial fish diets (30 min infusion of 100 mg in 100 ml), and various artificial and natural substances were tested. The most attractive amino-acids were lysine, methionine and alanine. Most of the dietary extracts tested did not stimulate feeding behaviour, indicating that widespread commercial sturgeon diets (such as ST-07 or ST-04Az) consist of components with little attractiveness for sturgeon fry. In most cases extruded diet components stimulated more bites than granulated ones. Among the diet components, only fish protein concentrate (FPC), dry milk and krill meal stimulated feeding behaviour. Flavour enhancers such as concentrated low molecular weight nitrogenous substancs (CLMNS), sodium glutamate, and "Finnstim" all stimulated feeding behaviour of fry. Some of these substances are recommended as flavour enhancers in sturgeon diets.     

Morphological and histochemical peculiarities of the gut in the white sturgeon, Acipenser transmontanus.

The gut of adult sturgeon was examined. The oesophageal mucosa contained numerous caliciform cells, synthesizing both neutral and acidic glycoconjugates, the latter of the sialylated type. The deep tunica propria-submucosa contained lobules of multilocular adipose tissue, specially abundant during the cold season. The oesophageal tunica muscularis was made up of a large sheath of striated muscle fibres, arranged orthogonally to a thin, subserous smooth muscle layer. The siphon-shaped stomach showed a ciliated epithelium in cardiac and gastric proper gland zones, where tubular glands were present in the tunica propria. The columnar cells which composed the superficial epithelium and gastric pits were demonstrated to synthesize almost exclusively neutral glycoconjugates. Appendices pyloricae constituted a glandular body equipped with intestinal mucosa. The intestinal mucosa was organized in folds, containing numerous caliciform cells which synthesized neutral or acidic glycoconjugates, the latter either of the sialylated and sulphated type. The sulphoglycoconjugates were more abundant in the caliciform cells of the distal intestinal tracts. The tunica propria-submucosa of the spiral valve (medium intestine) contained lymphatic tissue and large lymphatic follicles. A muscularis mucosae was present only in the rectum, where in addition a peculiar granular cell type was present in the superficial tunica propria-submucosa, possibly related to defensive properties. The subserous connective tissue contained pancreatic lobules all along the stomach and intestine. The enteric nervous system showed some special aspects, the most intriguing of which was the presence of large, longitudinally oriented nerve bundles in the t. propria-submucosa of oesophagus and cardiac stomach. The nerve bundles contained, near unmyelinated nerves, some myelinated nerves, as well as neuronal bodies. Both these aspects are exceptional in vertebrates and obscure in their significance. The structural and histochemical aspects we here describe are in part different from those described for other fish. Some of these special features are possibly related with special functional roles, others require a deeper insight and different approaches to clarify them functionally.     

Osmotic and ion regulation in different species of acipenserids (acipenseriformes, acipenseridae)

Species specificity of osmotic and ion regulation in five species of acipenserids connected in varying degrees with sea conditions is investigated. The objects of study were freshwater middle-Volga sterlet Acipenser ruthenus; Siberian sturgeon A. baerii, inhabiting the Lena River and migrating to the sea near the river mouth; and the following migratory acipenserids of the Volga-Caspian Basin (regular diadromous migrations): the Russian sturgeon A. gueldenstaedtii, the great sturgeon Huso huso, and the starred sturgeon A. stellatus. The study was carried out on immature specimens (of age 2+). The level of osmolarity and concentrations of cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) were determined in blood serum, urine, and liquid from the cavity of spiral valve in fish from the fresh water (control) and after their adaptation (period of seven to ten days) to sea water with salinity 12.5–12.7 and 18‰. The increase was found in the functional activity of the mechanism of osmotic and ion homeostasis in sturgeons according to the increase of the environmental salinity of a particular species. The freshwater sterlet adapted to the sea environment as osmoconformer. The other studied species were capable of maintaining a relative stability of osmolarity and ion concentration in blood serum at different levels while adapting to the sea environment; they changed from hyperosmotic (in fresh water) to hypoosmotic type of regulation. The kidney plays a more significant role in the removal of excessive Na⁺ in sturgeons than in bony fish. An increase in the sodium-reabsorption and magnesium-secretion functions of the kidney as well as the sodium-absorption function of the intestines was observed in sturgeons, relative to the increase of environmental salinity.