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.     

First evidence of hybridization between endangered sterlets (Acipenser ruthenus) and exotic Siberian sturgeons (Acipenser baerii) in the Danube River

Most natural populations of Eurasian sturgeons have declined dramatically during recent decades, reaching historic low levels today. During the same period, sturgeon has become very popular in European aquaculture. Because many hatcheries are located near rivers, their unintentional escape is often documented, especially during floods. Until now, no cases of successful hybridization of these escaped fish with wild stocks have been reported. In this study, the genetic structure of a highly threatened population of sterlets (Acipenser ruthenus) from the Upper Danube was analysed as a requirement for their conservation. Surprisingly, we observed genotypes and morphotypes of Siberian sturgeon (Acipenser baerii), as well as hybrids between this species and native sterlets. This hybridization poses a serious threat for the survival of this isolated sterlet population in the upper part of the Danube. For the first time, natural reproduction is documented for Siberian sturgeon outside their natural range in Europe. This finding demonstrates the risk of extinction by hybridisation of endangered populations. We would like to stress that taking into consideration the risks for native sturgeon populations, farmed sturgeon should not be released into the wild, and all measures should be taken to prevent their accidental escape.     

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.     

Exotic sturgeons in the Vistula Lagoon in 2011, their occurrence,diet and parasites,with notes on the fishery background

The Siberian sturgeon Acipenser baerii and the sterlet Acipenser ruthenus were recorded for the first time in the Vistula Lagoon in 2011. Among 66 sturgeons collected between April and December 2011, the Siberian sturgeon was the most numerous species (77%); however, a significant seasonal variability was observed, with sterlet dominating in the catches in late autumn of the same year. The stomach contents of the two species differed widely: Siberian sturgeon (14.9–42.2 cm standard length, SL) fed on crustaceans (Cercopagis pengoi, Oithona sp., Neomysis integer) (10.7% IRI), larvae and pupas of insects (Chaoborus sp., Chironomus sp., Polypedilum sp., Procladius sp., Culex sp.) (88.9% IRI) and fishes (Neogobius melanostomus, Osmerus eperlanus) (0.5% IRI), whereas sterlet (24.0–34.4 cm SL) consumed crustaceans (N. integer) (64.3% IRI), larvae of insects (Chironomus sp., Polypedilum sp.) (20.3% IRI) and fish (N. melanostomus) (15.4% IRI). Single Siberian sturgeon (4.3%) were found to harbour the parasitic nematode (Raphidascaris acus).     

Comparative protein profiles: Potential molecular markers from spermatozoa of Acipenseriformes (Chondrostei,Pisces)

Sturgeon and paddlefish (Acipenseriformes), the source of roe consumed as caviar, are a unique and commercially valuable group of ancient fishes. In this study, comparative proteomics was used to analyze protein profiles of spermatozoa from five sturgeon species and one paddlefish: Siberian sturgeon (Acipenser baerii), sterlet (A. ruthenus), Russian sturgeon (A. gueldenstaedtii), starry sturgeon (A. stellatus), beluga (Huso huso), and Mississippi paddlefish (Polyodon spathula). Protein profiles of spermatozoa were determined by isoelectric focusing and two-dimensional electrophoresis (2-DE) high-resolution gels. The peptides, previously selected by 2-DE analysis as potentially species-specific, were obtained by “in-gel” tryptic digestion, followed by matrix-associated laser desorption/ionization time-of-flight/mass spectrometry (MALDI-TOF/MS). Among the 23 protein spots selected, 14 were identified as isoforms of enolase B present in all species, but with different isoelectric points or molecular mass. Exceptions were A. ruthenus and H. huso, species with a close phylogenetic relationship. Glycerol-3-phosphate dehydrogenase was detected exclusively in P. spathula. Phosphoglycerate kinase was detected only in A. ruthenus and H. huso, and 3 additional proteins (fructose bisphosphate aldolase A-2, glycogen phosphorylase type IV and glyceraldehyde-3-phosphate dehydrogenase) were found exclusively in A. gueldenstaedtii and H. huso. This study points to the application of proteomics for differential characterization and comparative studies of acipenseriform species at the molecular level.     

Morphology and ultrastructure of Siberian sturgeon (Acipenser baerii) spermatozoa using scanning and transmission electron microscopy

BACKGROUND INFORMATION: Available data concerning the sperm morphology of teleost fishes demonstrate wide variation. In the present study, the spermatozoa of Siberian sturgeon (Acipenser baerii Brandt, 1869), a chondrostean fish, was investigated. In contrast with teleost fish, chondrostean spermatozoa have a head with a distinct acrosome, whereas other structures, such as a midpiece and a single flagellum, are present in spermatozoa of most species. RESULTS: The average length of the head including the acrosome and the midpiece was 7.01+/-0.83 microm. Ten posterolateral projections derived from the acrosome were present on a subacrosomal region, with mean lengths of 0.94+/-0.15 microm and widths of 0.93+/-0.11 microm. The nucleus consisted of electrodense homogeneous nuclear chromatin. Three intertwining endonuclear canals, bound by membranes, traversed the nucleus longitudinally from the acrosomal end to the basal nuclear fossa region. There were between three and six mitochondria, two types of centrioles (proximal and distal) in the midpiece and two vacuoles composed of lipid droplets. The flagellum (44.75+/-4.93 microm in length), originating from the centriolar apparatus, had a typical 9+2 eukaryotic flagellar organization. In addition, there was an extracellular cytoplasm canal between the cytoplasmic sheath and the flagellum. CONCLUSIONS: A principal components analysis explained the individual morphological variation fairly well. Of the total accumulated variance, 41.45% was accounted for by parameters related to the head and midpiece of the sperm and the length of the flagellum. Comparing the present study with previous studies of morphology of sturgeon spermatozoa, there were large inter- or intra-specific differences that could be valuable taxonomically.     

Molecular identification and the features of genetic diversity in interspecific hybrids of Amur sturgeon ( Acipenser schrenckii × A. baerii, A. baerii × A. schrenckii, A. schrenckii × A. ruthenus , and A. ruthenus × A. schrenckii ) based on variability of multilocus RAPD markers

The method of polymerase chain reaction with random primers (RAPD PCR) was used to identify the progeny of the crosses between three sturgeon species, Amur sturgeon (Acipenser schrenckii Brandt, 1869), Siberian sturgeon (A. baerii Brandt, 1869), and sterlet (A. ruthenus Linnaeus, 1758). Using ten primers, genetic variation in 70 yearlings, produced in seven individual crosses: Acipenser schrenckii × A. schrenckii, A. baerii × A. baerii, A. ruthenus × A. ruthenus, A. schrenckii × A. baerii, A. baerii × A. schrenckii, A. schrenckii × A. ruthenus, and A. ruthenus × A. schrenckii was described and evaluated. It was demonstrated that the samples composed of hybrids from individual crosses were more variable than the samples of parental species. On the other hand, pooled samples of hybrids from two cross directions were genetically less variable than the pooled samples of their parents. The three main features of the hybrid RAPD profiles identified included: (1) preservation of marker DNA fragments of both parents in one genome; (2) presence of specific DNA fragments, absent from both parents; and (3) dependence of the frequency of some DNA fragments from the cross direction. Multidimensional scaling clearly distinguishes in the space of three coordinates the individuals of original species and the hybrid progeny with differentiation in the groups of direct and backcross hybrids. Analysis of relationships (UPGMA and NJ) pointed to substantial differentiation between the species, as well as between the species and hybrid progeny. Close genetic relationships between direct and backcross hybrids were demonstrated. Multilocus RAPD markers in association with statistical methods are considered to be the useful tool for discrimination of interspecific hybrids of sturgeon. Possible reasons for the differences in the hybrid RAPD profiles are discussed. Original Russian Text ? K.V. Rozhkovan, G.N. Chelomina, E.I. Rachek, 2008, published in Genetika, 2008, Vol. 44, No. 11, pp. 1453–1460.     

Fine structure and morphology of sterlet (Acipenser ruthenus L. 1758) spermatozoa and acrosin localization

Ultrastructure of sterlet Acipenser ruthenus L. 1758 sperm was examined by scanning and transmission electron microscopy, which allowed us to use various methods for visualizations of different parts of sterlet spermatozoa. Sperm cells possess a head with a distinct acrosome, a midpiece and a single flagellum surrounded by the flagellar plasma membrane. The average length of the head including the acrosome and the midpiece was estimated as 5.14+/-0.42 microm. Nine to 10 posterolateral projections were derived from the acrosome. Three inter-twining endonuclear canals bounded by membranes traversed the nucleus in its whole length from the acrosome to the implantation fossa. Acrosin was located in all the three parts (acrosome, endonuclear canals and implantation fossa). The proximal and distal centrioles located in the midpiece compacted of nine peripheral triplets of microtubules. One cut of the midpiece contained from two to six mitochondria with area of 215+/-85 nm(2) in average. The flagellum was 42.47+/-1.89 microm in length with typical eukaryotic organization of one central pair and nine peripheral pairs of microtubules. It passed through a cytoplasmic channel in the midpiece, which was formed by an invagination at the plasmalemma. The flagellum gradually developed two lateral extensions of its plasma membrane, so-called "fins". Detected morphological variation can be described by four principal component axes corresponding to groups of individual morphometric characters defined on the sperm structures. Correlations among the characters indicate that the sperms are variable in their shape rather than size. Significant variation among examined fish individuals was found only in flagellum and nucleus length. Comparison between the present and previous studies of morphology of sturgeon spermatozoa confirmed large inter- and/or intra-specific differences that could be of substantial taxonomic value.     

Energy pathways associated with sustained spermatozoon motility in the endangered Siberian sturgeon Acipenser baerii

Sturgeon spermatozoa are unique for their sustained motility. We investigated the relative importance of bioenergetic pathways in the energy supply of Siberian sturgeon Acipenser baerii spermatozoa during motile and immotile states. Spermatozoon motility and oxygen consumption rate (OCR) were analysed following exposure to inhibitors of oxidative phosphorylation (sodium azide, NaN₃), glycolysis (2-deoxy-D-glucose, DOG) and β-oxidation of fatty acids (sodium fluoride, NaF), and to an uncoupler of oxidative phosphorylation (carbonyl cyanide m-chlorophenyl hydrazine, CCCP). No significant difference in curvilinear velocity was observed after addition of these reagents to activation medium (AM) or nonactivation medium (NAM) for incubation. Incubation of spermatozoa in NAM containing CCCP or NaN₃ resulted in significantly decreased motility duration compared to controls. The OCR of sturgeon spermatozoa in AM (11.9 ± 1.4 nmol O₂ min⁻¹ (10⁹ spz)⁻¹) was significantly higher than in NAM (8.2 ± 1.5 nmol O₂ min⁻¹ (10⁹ spz)⁻¹). The OCR significantly declined with addition of NaN₃ to AM and NAM. No significant difference in motility parameters or OCR was observed with NaF or DOG. These results suggest active oxidative phosphorylation in both immotile and motile spermatozoa. Nevertheless, mitochondrial respiration occurring during motility is not sufficient to meet the high energy demands, and the energy required for sustained motility of Siberian sturgeon spermatozoa is derived from adenosine triphosphate accumulated during the quiescent state.     

Content of cysteine, reduced and oxidized glutathione in spermatozoa of representatives of Acipenseriformes (Acipenser baerii and A. ruthenus) as well as teleosts (Perca fluviatilis and Sander lucioperca)

Glutathione belongs to a vital intra‐ and extra‐cellular protective antioxidant and is found almost exclusively in its reduced form. The ratio between its reduced and oxidized within cells is often used as a marker of cellular toxicity. The objectives of the study were to (i) determine both the reduced (GSH) and oxidized glutathione (GSSG) and cysteine (Cys) in the sperm of the Acipenser baerii and Acipenser ruthenus, as well as in Perca fluviatilis and Sander lucioperca, and (ii) to demonstrate the differences in concentration levels between representatives of acipenseriform and teleost species. High performance liquid chromatography with electrochemical detection was employed. The average content of the thiols determined in the sperm samples were as follows: Acipenser baerii (cysteine 55 ± 8 μg ml^?1; GSH 126 ± 19 μg ml^?1; GSSG 49 ± 7 μg ml^?1), Acipenser ruthenus (cysteine 62 ± 9 μg ml^?1; GSH 768 ± 115 μg ml^?1; GSSG 180 ± 16 μg ml^?1), Sander lucioperca (cysteine 251 ± 38 μg ml^?1; GSH 185 ± 28 μg ml^?1; GSSG 93 ± 14 μg ml^?1), Perca fluviatilis (cysteine 281 ± 42 μg ml^?1; GSH 496 ± 74 μg ml^?1; GSSG 138 ± 21 μg ml^?1). Based on the results obtained it can be concluded that this method is sensitive and selective for the determination of these compounds in real samples. Results revealed differences in cysteine content between species of the two systematic categories but also showed that ratios between GSH and GSSG can vary between species while potentially predict oxidative stress in fish sperm.     

Flow cytometry for assessing the efficacy of interspecific gynogenesis induction in sturgeon

The efficacy of ploidy analysis for separating progeny of Siberian sturgeon Acipenser baerii after induced gynogenesis was demonstrated using sperm of a paternal species differing in ploidy level from the maternal species. Gynogenesis was induced in tetraploid A. baerii with UV‐C irradiated sperm from the diploid sterlet Acipenser ruthenus and vice‐versa. The success of sperm UV irradiation and diploidy restoration by heat‐shock was estimated based on the ploidy level of progeny, confirmed by microsatellite parentage assignment. Hatching rates of interspecific gynogenotes were comparable with rates reported for gynogenesis induction using sperm and eggs of the same species. Juvenile mortality was similar to that observed in the control hybrids. The efficiency and reliability of this method may foster its use for production of gynogenotes in aquaculture, potentially allowing interspecific gynogenesis to replace intraspecific.     

Cryopreservation of sterlet (Acipenser ruthenus) spermatozoa using different cryoprotectants

The present study examined the effectiveness of different cryoprotectan uses for cryopreservation of sterlet (Acipenser ruthenus) sperm. Four different cryoprotectans [dimethyl‐sulfoxide (DMSO), dimethylacetamide (DMA), ethyleneglycol (EG) and methanol (MET)] in concentrations of 5 and 10% in the extender media (30 mm sucrose, 1 mm KCl, 25 mm Tris–HCl pH 8.5) were used for the cryopreservation of sperm from five sterlet males. Percentages of motility, velocity, fertilization and hatching rate were measured. The highest post‐thawing motility was observed in sperm samples cryopreserved with 10% MET (46 ± 19%), 10% DMA (47 ± 18%) and 10% DMSO (45 ± 7%). Fertilization rate in the control (fresh sperm) was 69 ± 9% and the hatching rate 61 ± 8%. A higher hatching rate after cryopreservation was obtained with 10% MET (32 ± 17%) and 5% DMA (23 ± 3%) when compared to data obtained with 10% DMA (9 ± 5%), 5% MET and 5 and 10% DMSO, wherein the hatching rate was around zero. Our results demonstrate that DMA can be used for cryopreservation of sturgeon spermatozoa.     

Ultrastructure and morphology of spermatozoa in Chinese sturgeon (Acipenser sinensis Gray 1835) using scanning and transmission electron microscopy

The Chinese sturgeon (Acipenser sinensis Gray 1835) is an endangered anadromous sturgeon inhabiting the Yangtze River in China. In this study, the ultrastructure and morphology of spermatozoa was studied using transmission and scanning electron microscopy with a cryo-holder. The spermatozoon consisted of an elongated head with a distinct acrosome and nucleus region, a midpiece and a flagellum. The mean length of the head and midpiece, the flagellum and total length of spermatozoon were 4.48, 33.3 and 37.8 microm, respectively. The nucleus was an elongated trapezoid shape with anterior (acrosome) end narrower than the posterior. Granular material and an actin filament were observed within the anterior acrosome. Three to five endonuclear canals were present. The midpiece was eudipleural along its longitudinal axis. Compared to other sturgeon species, the data from the present study suggest a more recent evolutionary linkage between Chinese sturgeon and white sturgeon (Acipenser transmontanus Richardson 1836).     

A Comment on the Siberian, Acipenser baerii, and Russian, Acipenser gueldenstaedtii, Sturgeons

Contrary to the opinion of Kynard et al. (2002), the Siberian sturgeon, Acipenser baerii, does not belong to the Ponto-Caspian species. It inhabits Siberian rivers and Lake Baikal. Acipenser baerii is a typical potamodromous species and the comparison of the behavior of its embryos and larvae with those of the anadromous Russian sturgeon, Acipenser gueldenstaedtii, should be done with understanding that these species have different life histories. The statement by Kynard et al. (2002) that larvae of the Russian sturgeon do not migrate contradicts results of previous studies.     

The heterosis estimates for growth and survival traits in sterlet and Siberian sturgeon purebreds and hybrids

The aim of the present study was to estimate and compare the growth and survival traits of the hybrids and purebreds produced by crossing the Siberian sturgeon (Acipenser baerii) (S) and sterlet (Acipenser ruthenus) (St) in order to determine the heterosis effect in the F1 generation. We compared the breeding conditions, mean body weight (BW) and cumulative survival in the artificially produced hybrid crosses of sterlet and Siberian sturgeon with respect to their pure parental species in indoor and outdoor aquaculture systems at different developmental stages. Fertilization and hatching rates were found to be significantly higher in S × S purebred compared to St × S hybrid. The highest values of BW were recorded in St × S hybrid (557.54 ± 179.7 g) on 862 days post-hatch (dph) while the highest cumulative survival was recorded in S × S purebred (14.3%). The recorded cumulative survival and mean BW was significantly lower in St × St purebred. The highest positive heterosis was recorded for mean BW of St × S hybrid (51.3% on 862 dph) throughout the sampling points. The studied sturgeon hybrids had higher mean BW compared to St × St purebred under suboptimal rearing conditions. Although there was no clear demonstration of the superiority in performance of reciprocal hybrids over purebreds, the St × S hybrid can be used for achieving better productivity in aquaculture systems.     

Characteristics of arylsulfatase in Russian sturgeon (Acipenser gueldenstaedti) semen

Spermatozoa of sturgeons (Acipenseriformes), unlike teleosts, possess an acrosome. This paper provides data concerning biochemical characteristics of arylsulfatase (AS), an acrosomal enzyme, found in Russian sturgeon spermatozoa and seminal plasma. The enzymes were purified by a four-step procedure, using n-butanol extraction, ion-exchange chromatography repeated twice and gel filtration. High purity of our enzymes was confirmed by silver staining electrophoresis and an immunological experiment. Kinetic parameters indicated that the purified enzymes belong to arylsulfatase type A. Similarity of the seminal plasma arylsulfatase to the spermatozoan enzyme showed us that arylsulfatase from seminal plasma might originate from damaged spermatozoa. The possible physiological consequences of the presence of arylsulfatase in Russian sturgeon semen are discussed.     

Acrosome staining and motility characteristics of sterlet spermatozoa after cryopreservation with use of methanol and DMSO

In this study we describe acrosome staining and motility characteristics of fresh and cryopreserved sterlet (Acipenser ruthenus L.) spermatozoa using soybean trypsin inhibitor-Alexa conjugate fluorescent staining and computer-aided sperm analysis (CASA), respectively. Methanol or dimethylsulfoxide (DMSO) were used as cryoprotectants. After cryopreservation a decline in sperm motility characteristics occurred, but no differential effect between cryoprotectant was observed. Cryopreservation caused a significant increase in the percentage of spermatozoa with acrosome stained by SBTI-Alexa for samples cryopreserved using DMSO compared to methanol. These data suggest that the low usefulness of DMSO for cryopreservation of sturgeon spermatozoa is related to its harmful specific effect towards the acrosome, probably by causing its precocious triggering, much before any egg contact.     

Features of inheritance of several morphological characters in the hybrids between Siberian sturgeon <Emphasis Type="Italic">Acipenser baerii</Emphasis> and beluga <Emphasis Type="Italic">A. huso</Emphasis> (Acipenseridae) and in gynogenetic individuals of Siberian sturgeon

Comparative analysis of several morphological characters is conducted in experimentally obtained hybrids between Siberian sturgeon Acipenser baerii and beluga A. huso, in parental species, and in gynogenetic progeny of Siberian sturgeon. The gynogenetic individuals are similar to Siberian sturgeon by all characters used for differentiation between Siberian sturgeon and beluga that supports gynogenetic origin of these individuals. Based on the data obtained on the hybrid specimens, the features of inheritance of the studied characters in sturgeons and their variation in postlarval ontogeny are discussed.     

Use of Feulgen image analysis densitometry to study the effect of genome size on nuclear size in polyploid sturgeons

Feulgen image analysis densitometry (FIA) and image cytometry were used to study the relationship between the DNA content (pgDNA nucleus^?1) and nuclear area (μm²) in blood smears of evolutionary tetraploid (4n) sterlet (Acipenser ruthenus) and stellate sturgeon (A. stellatus); evolutionary octaploid (8n) Siberian sturgeon (A. baerii) and Russian sturgeon (A. gueldenstaedtii); hexaploid (6n) and decaploid (10n) fish found within A. baerii stock; and A. baerii and A. gueldenstaedtii exhibiting dodecaploidy (12n). Standards used for FIA were blood smears of chicken (Gallus gallus domesticus; 2.5 pgDNA nucleus^?1) and diploid and induced triploid tench, Tinca tinca (2.04 and 3.1 pgDNA nucleus^?1, respectively). All ploidy levels were first verified by means of flow cytometry. Species of the same ploidy level, however differing in their DNA content, exhibited a similar mean erythrocyte nuclear area, as could be demonstrated on A. ruthenus and A. stellatus (19.27 and 19.79 μm²_, respectively) with a respective mean DNA content of 3.72 and 4.68 pgDNA nucleus^?1 and the same relationship was found for evolutionary octaploid (8n) A. baerii and A. gueldenstaedtii (29.87 and 30.09 μm², respectively) with respective mean DNA content 8.29 and 7.87 pgDNA nucleus^?1. The 0.19–0.32 pgDNA increments in DNA content of erythrocytes thus had no effect on their nuclear area. With increasing ploidy level, the DNA concentration (pgDNA per μm² of erythrocyte nuclear area) was found not to increase linearly. The DNA in erythrocyte nuclei appeared to be more and more densely packed with an increase of the ploidy level (r = 0.98; R² = 0.95).     

Polymorphism of the mitochondrial DNA control region in eight sturgeon species and development of a system for DNA-based species identification

Intraspecific and interspecific nucleotide sequence variations of the mtDNA control region (D-loop) were studied with mtDNAs isolated from tissue specimens of more than 1400 sturgeons of nine species: Russian sturgeon Acipenser gueldenstaedtii, Persian sturgeon A. persicus, Siberian sturgeon A. baerii, Amur sturgeon A. schrenkii, Fringebarbel sturgeon A. nudiventris, sterlet A. ruthenus, stellate sturgeon A. stellatus, beluga Huso huso, and kaluga H. dauricus. The results were used to analyze the interspecific variation of the mtDNA control region in the given set of species and to develop a test system of ten species-specific primers, which allowed species identification from noninvasive tissue samples, spawn, and food products of eight species. The system proved suitable for multiplex PCR. A method was developed for the first time to reliably differentiate the A. baerii mitotype and the baerii-like mitotype of A. gueldenstaedtii. It was found that, although genetically separate, A. gueldenstaedtii and A. persicus are relatively young species and have common mitochondrial haplotypes, precluding their identification via mtDNA analysis alone. To develop a system for species identification of A. gueldenstaedtii and A. persicus, it is necessary to study the polymorphism of nuclear markers.