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The eastern part of the Black Sea and its tributaries are suitable habitats for several sturgeon species, among which Acipenser gueldenstaedtii, A. stellatus, A. nudiventris, A. persicus, A. sturio, and H. huso are well documented. However, different threats have led these species to a dramatic decline, all of them are currently listed as Critically Endangered, and some Locally Extinct, in that area. We tested 94 wild sturgeon samples from the Black Sea and Rioni River by analyzing the mitochondrial Control Region and nuclear markers for hybrid identification. The data analyses (1) assessed mitochondrial diversity among samples, (2) identified their species, as well as (3) indicated instances of hybridization. The data collected, besides confirming a sharp decrease of catches of Beluga and Stellate sturgeon in recent years, also revealed four juvenile hybrids between Russian and Stellate sturgeon, providing the first evidence of natural interspecific hybridization in the Rioni. The present communication raises concerns about the status of sturgeon species in this area and underlines the urgent need for conservation programs to restore self-sustaining populations.

In the past 50 years, habitat conditions and distribution of sturgeons in the Caspian Sea have significantly changed. The longest term records of sturgeon distribution are obtained for the northern part of the sea, which is extremely important for the feeding of these species. In the present review, we summarize and analyze changes in the distribution of the beluga Huso huso L., 1758; Russian sturgeon Acipenser gueldenstaedtii Brandt, 1833; and stellate sturgeon Acipenser stellatus Pallas, 1771 in the northern part of the sea from 1970 until 2014 and the biotic and abiotic factors of these changes. The effect of the sea-level fluctuations, the biomass of food organisms, and the total abundance of the studied fish species on their distribution is demonstrated.

The swimming ground speed and swimming depths of beluga sturgeon (Huso huso) and stellate sturgeon (Acipenser stellatus) were investigated using ultrasonic telemetry between 2011 and 2017 in the Lower Danube River (river kilometer (rkm) 0 Sulina-rkm 1075 Bazias). Acoustic telemetry receivers VR2W and V16TP tags (Vemco, Canada) were used to collect data about sturgeon migration behavior in the Lower Danube River between the Black Sea and the Iron Gate II dam. The tags, equipped with depth and temperature sensors, provided data about beluga and stellate sturgeon migration periods, swimming speeds, and depths. Twenty-three beluga sturgeon (184-245 cm TL) and twenty-one stellate sturgeon (92-135 cm TL) were ultrasonically tagged and passively tracked using hydrophone receivers installed in the river between rkm 71 and rkm 860. Three tagged beluga sturgeon returned after 2 and 5 years and two stellate sturgeon returned after 2 years since the time of their initial release in the river. This study provides, for the first time, further details concerning beluga sturgeon and stellate sturgeon migratory behavior patterns, traveled distances, swimming depths, and their swimming ground speeds during spawning migration.

The Hydro development started in the 1960s with building 3 major dams in the upstream section of the Sakarya River. During the 1980s the development of the floodplain sections of the river had its onset. Under these altered conditions Huso huso, Acipenser nudiventris , and Acipenser sturio disappeared from the river until the 1980s but Acipenser gueldenstaedtii, as well as Acipenser stellatus, were shown to still reproduce in the remaining section of the river by 2013. The construction of three additional HEPPs begun in the river section below Pamukova, blocking migration and cutting off major spawning sites. While fish passage facilities were included in the construction of the HEPPs since the 1980s, their design and location, as well as the maintenance rendered them completely dysfunctional. A survey was carried out in the remaining free flowing section of the lower river in 2014 to determine fish commun ity composition and water quality at 4 stations below Adasu HEPP. While a few A. gueldenstaedtii juveniles were observed in Sakarya River mouth close to the Black Sea, only one young-of-the- (YOY) ( A. stellatus ; W:25g; TL:28cm) was reported which was captured from the Lower Sakarya River.

—Data based on the results of published, unpublished, and questionable materials concerning the occurrence of anadromous sturgeons after damming of the Don River downstream and upstream of the Tsimlyansk hydroengineering complex are presented. Two peaks of approaches of spawners to the dam in the 1950s and 1980s were recorded. The first peak was related to the wild population that existed in these years; the second peak was a result of mass artificial propagation. At the first stage, the Russian sturgeon (Acipenser gueldenstaedtii Brandt et Ratzeburg, 1833) and the beluga sturgeon (Huso huso (Linnaeus, 1758)) prevailed downstream from the dam; at the second stage, only the Russian sturgeon was recorded. Since 1955, only 21 individuals of anadromous sturgeons have made it through the dam by a fish ladder. During the years 1952–1961, 1145 individuals were transported into the reservoir, including 218 ind. of beluga. Some individuals of beluga were transported later as well. There are data indicating the presence of juvenile beluga individuals that originated from natural spawning in the reservoir before the 1970s. The last known spawners of Russian sturgeon and stellate sturgeon (Acipenser stellatus Pallas, 1771) in the reservoir were recorded in the 1980s or 1990s. Solitary beluga individuals may occur nowadays. It is suggested that the youngest of the noted individuals belong to the generations of the early 1990s. It is concluded that the extremely innumerous landlocked form of the Azov beluga may still exist in the reservoir.

Sturgeon is one of the ancient fish species with the fossil records over 200 million years ago. However, the sturgeon genomes are rather complicated, owing to several rounds of genome polyploidizations, which makes it difficult to assemble a high quality genome so that only a few studies analyze their whole genome evolutions (WGDs). This study applied the PacBio sequencing technology to sequence the full-length transcriptomes of blood samples of octoploid Huso dauricus, octoploid Acipenser schrenckii and tetraploid Acipenser stellatus. A total of non-redundant 33,407 transcript assemblies of the three sturgeons were finally generated and fully annotated with different gene function databases, as well as the predictions of simple sequence repeats, transcription factors and long non-coding RNAs. Data valuation exhibited that annotations of the three transcriptomes had the higher quality than those of the previously sequenced sturgeon genomes. A phylogeny of eight typical sturgeons was constructed using the low copy genes, which illustrated that Acipenser and Huso might share a single origin. The sturgeon WGDs were parallelly timed by calculating the divergence times of 2-member gene clusters and heterozygous-SNP-carried genes, which both suggested the occurrence of the WGDs later than 150 mya. The full-length transcriptome sequences were supposed to be the reliable reference data for the study of sturgeon.

The present study investigated metal accumulation in the muscle of the Caspian sturgeons, Acipenser nudiventris, Acipenser persicus, Acipenser stellatus and Huso huso with different feeding niches, condition factor, body size and age, sampled in the spring of 2014, using an ICP-OES (Shimadzu). We used redundancy analysis to examine relationship between metals concentrations and the measured variables in the species. Huso huso specimens tended to have a higher concentration of Ba, Cr, K and Mn relative to the other species. Most metals had positive correlations with the body length, weight and age. Condition factor was not correlated with other parameter measured. The mean concentrations of the measured metals in muscles were higher than those of previous studies of sturgeons from the Caspian Sea suggesting increased pollution. The present study suggests that non-dietary sources of metals may play an important role in the accumulation of metals in the muscles of sturgeons.

Based on the literature, non-published and survey data, information on the occurrence of anadromous sturgeons after the regulation of the Don River downstream and upstream of the Tsimlyansk Dam is given. There were two peaks of mature adults approaching the dam, namely, in the 1950s and 1980s. The first mass peak was associated with the wild population existed then; the second one was a result of mass artificial breeding. At the first stage, the sturgeon (Acipenser gueldenstaedtii Brandt et Ratzeburg, 1833) and beluga (Huso huso (Linnaeus, 1758)) prevailed below the dam; at the second one, just the sturgeon did. Since 1955, only 21 individuals of anadromous sturgeons were transported through the dam by a fish ladder. During 1952-1961, 1,145 individuals were transported into the reservoir, including 218 belugas. Separate beluga individuals were transported later on as well. There is evidence of the presence of young beluga individuals from natural spawning in the reservoir before the 1970s. The latest known adult sturgeon and stellate sturgeon (Acipenser stellatus Pallas, 1771) in the reservoir were noted in the 1980-90s. Separate beluga individuals have been met until now. The youngest of the noted individuals belong roughly to the generations of the early 1990s. It is concluded on the existence of an extremely low-abundant landlocked form of the Azov beluga in the reservoir.

Data on distribution of digestive enzymes along the intestinal tract of mature specimens of the beluga Huso huso and Russian sturgeon Acipenser gueldenstaedtii are presented. The absence of a distinct proximo-distal gradient of the enzyme activity can be explained by short length of the intestine of sturgeons. Considerable differences are found in the distribution pattern of enzymes along the intestinal tract of beluga and Russian sturgeon. The effect of the method of calculation of the enzyme activity on the data on the proximo- distal gradient is considered.

In the Lower Danube, sturgeon populations have declined dramatically in recent decades. Although efforts have been made at the legislative level since 2006, by forbidden commercial fishing, an assessment of stocks and conservation status of sturgeon species has not yet been made [1]. In this context, it is necessary to estimate the age and growth rate of sturgeon species in order to establish their current conservation status, with a high level of confidence. This article presents the long-term results obtained by INCDPM during 6 years of research in which were captured and released 108 specimens of beluga (Huso huso) and 193 specimens of stellat sturgeon (Acipenser stellatus). Thus, before the ultrasonically tagging of the sturgeon specimens, informational volumes regarding the biometric parameters were collected simultaneously with the gender determination [1]. Based on the collected data and the calculus hypotheses, it was possible to determine the ages of the sturgeon specimens and to perfect the method of improving the confidence level of the data obtained from the in-situ investigations. In order to foster sustainable management of Danube sturgeon populations, it is essential to carry out assessments with a high degree of confidence of the age of anadromous sturgeon species. The quantification of the population depends on species spawning cycles taking into account that they are characterized by high longevity.

The developmental changes in blood proteins of three sturgeons genera Acipenser, Huso, and Pseudoscaphirhynchus (fam. Acipenseridae), have been studied using immunological methods. Heterochronicity and staging of protein development are revealed. Initially, proteins defining the specificity of immunoelectrophoregrams and subject to inconsiderable changes with fish growth are formed. The formation of transferrins is completed in the latest turn. Patterns of development do not depend on the ecology of anadromous and potamodromous forms of sturgeons. This results in the monotypic immunoelectrophoregrams of blood proteins in adult individuals of ten fish species. It is suggested that the variability of blood proteins in the ontogenesis of sturgeons reflects the evolution of this fish through consecutive adaptation to sea waters of different salinities and transition of ancient ancestors to the anadromous mode of life under conditions of oceanic salinity. The modern potamodromous sturgeons may have originated as a result of the return of anadromous forms to life in fresh waters.

The catch rates and the catch composition of lost nets were investigated during two seasons (fall and winter) in the southern Caspian Sea. A total of 167 surveys were conducted using anchor to retrieve ghost nets, which led to recover a total of 515 monofilaments gillnet. The most abundant caught species in during both seasons was belonged to Alosa caspia (52.1–43.9%). At both seasons, individuals of Huso huso, and Acipenser stellatus were substantially caught below the length at first maturity. The highest mean of catch rates was discovered at 0–10 m depth (2.79 kg), while the depth of 10–20 m provided the lowest amount of catch (2.0 kg). The Spearman correlation test showed that an increase in depth is reflected in lower values of the retrieved ghost nets. Overall, this study revealed that ghost gillnets is widely distributed in the southern Caspian Sea, mainly at the shallow waters.

Analysis of dynamics of commercial catches and the state of populations of Russian sturgeon Acipenser gueldenstaedtii, starred sturgeon A. stellatus, and great sturgeon A. huso (Huso huso) in the Caspian Sea is presented. In the retrospective, the role of natural and artificial reproduction in formation of populations of Acipenseridae sturgeons is considered. The main principles of rational organization of practical activity for preservation and restoration of populations of Acipenseridae sturgeons are formulated.

The study on histological characteristics of the digestive system of Beluga (Huso huso) was conducted from hatching until 50 days posthatching at 16.5 °C. Development of the digestive system in this species followed the general pattern described for other Acipenserids, although there were differences in the timing of organ development among species. At hatching, the mouth was opened and digestive system was represented by a gastric cavity filled with yolk and lined by endodermal cells, and a partially differentiated hindgut. Gastric glands started to differentiate at 46.5 degree- days posthatching (ddph), the earliest appearance time among sturgeon fishes studied to date. At the onset of exogenous feeding (144.9 ddph), yolk sac reserves were not completely depleted in the stomach, suggesting a period of mixed nutrition. The complete development of the digestive system was not accomplished until 235.2 ddph when it showed all histomorphological features typical of juvenile specimens. According to histological results, it seems advisable to start co-feeding H.huso larvae with inert diets at the onset of exogenous feeding, because exocrine pancreas and glandular stomach are fully differentiated, although the complete substitution of live prey by inert feed is not recommended until 235 ddph.

The accumulations of Cd, Pb and Zn were determined in edible and inedible tissues of Persian sturgeon ( Acipenser persicus ; n = 27), stellate sturgeon ( Acipenser stellatus ; n = 5) and beluga ( Huso huso ; n = 4) collected from coastal waters of the South Caspian Sea from March to April 2011. Concentrations of metals evaluated in the caviar, muscle, liver, kidney, gills, ovary and heart of the three species of sturgeons have been assessed using the flame and graphite furnace atomic absorption spectrophotometer. Concentrations of Zn, Pb and Cd in the edible and inedible tissues were apparently different among the three species of sturgeons. Especially, beluga heart showed the highest concentrations of Zn and Pb and Cd in Persian sturgeon liver. The analyzed metals were found in the caviar and muscle samples of Persian sturgeon and likewise muscle samples two other sturgeon species at mean concentrations under the permissible limits proposed by MAFF (2000) .

Iridoviridae are known to cause disease in sturgeons in North America. Here, histological and molecular methods were used to screen for this family of virus in sturgeons from various European farms with low-to-high morbidity. Some histological samples revealed basophilic cells in the gill and labial epithelia, strongly suggesting the accumulation of iridovirus particles. Newly developed generic PCR tests targeting the major capsid protein (MCP) gene of sturgeon iridoviruses identified in North America, namely the white sturgeon iridovirus and the Namao virus (NV), produced positive signals in most samples from four sturgeon species: Russian (Acipenser gueldenstaedtii), Siberian (A. baerii), Adriatic (A. naccarii) and beluga (Huso huso). The sequences of the PCR products were generally highly similar one another, with nucleotide identities greater than 98%. They were also related to (74-88%), although distinct from, American sturgeon iridoviruses. These European viruses were thus considered variants of a single new virus, provisionally named Acipenser iridovirus-European (AcIV-E). Moreover, three samples infected with AcIV-E showed genetic heterogeneity, with the co-existence of two sequences differing by five nucleotides. One of our European samples carried a virus distinct from AcIV-E, but closely related to NV identified in Canada (95%). This study demonstrates the presence of two distinct sturgeon iridoviruses in Europe: a new genotype AcIV-E and an NV-related virus.

Caspian biodiversity protection is mainly focused on the recovery of a few valuable commercial species such as beluga (Huso huso Linnaeus), Russian sturgeon (Acipenser gueldenstaedtii Brandt), Persian Sturgeon (Acipenser persicus Borodin), Ship Sturgeon (Acipenser nudiventris Lovetsky) and stellate sturgeon (Acipenser stellatus Pallas) and Caspian Salmon (Salmo trutta caspius Kessler) which are currently endangered. Apart from these species, biodiversity change and especially habitats destruction are poorly traced and managed in the region. The Caspian genetic biodiversity is insufficiently known and restocking programmes have hardly taken into consideration the need to protect it.

In this work, we investigated the effects of various feeding treatments on the survival and growth of Huso huso and Acipenser persicus larvae during a 20-day culture period. Three replicate groups (250 fish/replicate) of first-feeding larvae were fed according to four main feeding regimes: (1) live food (live nauplii of brine shrimp Artemia urmiana); (2) indirect transition (5–7 days live food followed by gradual transition to formulated diet); (3) direct transition (using different combinations of live and formulated diet from the start feeding onwards); and (4) formulated feed (FD) from the start of feeding. In H. huso larvae, combining live food and manufactured diets (co-feeding) from the first feeding stage onwards (direct transition) resulted in significantly higher weight gain than the other regimes. Survival was significantly higher in H. huso larvae fed solely live food or the direct transition regimes compared with indirect transition and FD. In A. persicus larvae, growth and survival were higher in the indirect transition feeding regime than in the other regimes. On the basis of the results of this study, we recommend co-feeding of H. huso immediately from the commencement of exogenous feeding, but co-feeding of A. persicus should start 7 days after prior feeding with live food.

Summary The aim of this report is to provide an overview of the current status of efforts on the potential rehabilitation of sturgeon populations in Turkish waters, describing the structure and the outcome of projects carried out since 2006 and identifying the strategic needs for sturgeon conservation measures at a national level. It is well known that there were six sturgeon species occurring around Turkish Black Sea coasts while entering the rivers, mainly Kizilirmak, Yesilirmak, Sakarya and Coruh Rivers for spawning. Anadromous sturgeon species have been strictly protected throughout Turkey since 1997. Conservation and management measurements have been implemented since 1970s. However, this was apparently with little success as stocks continued to decline and habitats deteriorated further, threatening the stocks with extinction. At the same time the needs for survival are not well documented. A project was initiated on 30 January 2006, consisting of seven-work packages including studies on population structure, reproduction, habitat assessment, genetic variability between and within stocks and the development of protective management strategies and plans. The work covered the Turkish Black Sea coastline and the rovers Yesilirmak, Kizilirmak, Coruh and Sakarya. Actively sampled and/or accidentally caught specimens have been tagged by T-bars and released after measurements and tissue sampling for genetic analyses. In addition, broodstocks of Russian sturgeon (Acipenser gueldenstaedtii), Beluga (Huso huso), and stellate (A. stellatus) are being built by rearing fish at the Central Fisheries Research (Yomra, Trabzon, Turkey) Institute. Reproduction studies have mainly focused on sperm collection, cryopreservation and induced spawning as well as on larval rearing.

Summary The effects of feeding Acipenser persicus and Huso huso larvae with Artemia nauplii enriched with ascorbyl palmitate (AP) and lipid emulsions on inducing tolerance against abrupt changes in environmental conditions (such as elevated levels of salinity, temperature, nitrite and total ammonia) were investigated. The 10 days post-hatch fish larvae were fed with decapsulated cysts (DC) or newly hatched Artemia urmiana nauplii enriched with saturated lipids and HUFA emulsions containing 0, 10, and 20% AP. The control groups received non-enriched nauplii as source of food. Each feeding experiment was carried out for 15 days in four replicates under controlled laboratory culture conditions. Ten randomly collected A. persicus and H. huso larvae from each replicate were subjected to different salinities, nitrite, total ammonia concentrations and temperatures. The results showed that feeding with Artemia nauplii enriched with HUFA and higher concentrations of vitamin C induces significantly higher tolerance to shocks in abiotic conditions in fish larvae of both species, as shown by higher survival. Nevertheless the two fish species did not exhibit a similar pattern of response: A. persicus showed higher tolerance compared to H. huso. Enrichment with HUFA alone did not result in a significantly improved tolerance, indicating the importance of dietary vitamin C to cope with abrupt physico-chemical changes.

The aims of this study was to assess the effect of two lactic acid bacteria (LAB), Lactobacillus curvatus and Leuconostoc mesenteroides, originally isolated from gastrointestinal (GI) tract of beluga (Huso huso) and Persian sturgeon (Acipenser persicus), respectively, on growth, survival and digestive enzyme (amylase, lipase and protease) activities and the population level of LAB in the GI tract. The treatments included 10 different groups; control, separate supplements of L. curvatus and Leu. mesenteroides at three different counts [2 × 109, 5 × 109 and 9 × 109 colony forming units (CFU) per gram food] and three combinations of the two LAB (2 × 109 + 2 × 109, 5 × 109 + 5 × 109 and 9 × 109 + 9 × 109 CFU per gram food). The bacteria used in this study were added in lyophilized form to chopped Chironomidae. In the beluga study, highest specific growth rate, survival and improved intestinal enzyme activities were noted in the rearing group fed 9 × 109 L. curvatus per gram food. In Persian sturgeon, the inclusion level of 2 × 109 Leu. mesenteroides had similar positive effect. The ability of LAB to colonize the digestive tract seems to involve host specificity, and our bacteriological results are relevant to initiate future probiotic studies in sturgeons and future directions will be discussed.

Sturgeon populations in the Danube River have experienced severe decline during the last several decades, mostly due to the poorly regulated fishery, river fragmentation and water pollution. This study focuses on gaining better understanding of sturgeon life history primarily by addressing the assessment of microelement accumulation in sturgeon pectoral fin rays, especially of strontium and calcium, as a method that can reveal migration patterns of anadromous sturgeons. Analysis was performed on pectoral fin samples of three anadromous Danube sturgeon species (beluga, Russian sturgeon and stellate sturgeon) by the use of a Nuclear Microprobe technique. The most frequent pattern in analyzed samples was represented by a low Sr:Ca ratio in the innermost annuli, followed by an increased ratio in the middle annuli segment, and often with a decreased ratio in the outermost annuli. Probability density estimate has revealed three distinguished maxima of the Sr:Ca ratio, 7.08×10 �3 , 8.98×10 �3 and 9.90× 10 �3 , which might correspond, respectively, to fresh, brackish and saltwater. Although the analysis of the Sr:Ca ratio in sturgeon pectoral fin rays has revealed changes that might indicate probable migration between habitats with different water salinity, further studies are needed for improvement of this method. This study represents the first analysis of this kind that was conducted on sturgeon species from the Black Sea basin.

Results are described of experimental crossing for obtaining of triple hybrids of the Russian sturgeon Acipenser gueldenstaedtii, the great sturgeon A. huso, and the starred sturgeon A. stellatus and of comparative analysis of some quantitative morphological characters in these hybrids, in the progeny of parental species and of reciprocal hybrids of starred sturgeon and great sturgeon. By most investigated characters, in triple hybrids, the states of the paternal species (Russian sturgeon) are inherited, by some other characters-of great sturgeon-the state of starred sturgeon is not inherited. Therefore, on the basis of external appearance, they may be identified as the hybrid of Russian sturgeon with great sturgeon. The observed segregation by the form of gill rakers into paternal, maternal, or intermediate variants leads to a conclusion of nonmonogenous inheritance of a wide form and a conical form of gill rakers in sturgeons. On the whole, the obtained results clearly demonstrate how, due to effects of matrocliny and partocliny, and different combination of dominant and recessive alleles of the genes determining the diagnostic characters, the hybrid individuals may acquire a different extent of similarity and differences from the parental species. The investigated triple hybrids are an interesting example of mutual leveling of divergent traits in the course of combination of different genomes within limits of one closely related Atlantic group of sturgeons. As a result, a certain averaged habitus is formed which might take place also in case of formation of polyploidy species in the process of evolution.

Construction of the dams in Lower Danube River (LDR- rkm 0 Sulina – rkm 1075 Baziasi) without fish passages, as well as illegal fishery and river bottom modification due to navigation had negative impact on sturgeon’s populations. Beluga Sturgeon, Stellate Sturgeon and Russian Sturgeon still migrate to spawn in LDR but there is lack of information relating to sturgeons long distance migration in this area. Tagging with Vemco V16 TP acoustic tags, equipped with temperature and depth sensors involved 36 adult Beluga and 44 Stellate Sturgeons provide new data about sturgeon migration. Their migrations are monitored by VR2W receivers, deployed on between rkm 71 and rkm 864. Analysis of data showed that 17% of Beluga and 30% of Stellate Sturgeon never recorded and 30% and 11% of Beluga and Stellate Sturgeon recorded in period more than 30 days after tagging. Only 5% of Beluga and 7% of Stellate Sturgeon have been recorded after a period of more than 1 year. During 2013-2016 4 adult Beluga and 1 adult Stellate Sturgeon were recorded in the IGII Dam area. Results of this investigation showed that sturgeons still approached the IG2 dam and construction of fish passage on this dam is needed.

Some quantitative characters of three-summer old reciprocal hybrids of beluga Acipenser huso and starred sturgeon A. stellatus,as well as of juveniles of their parental species, are comparatively analyzed. The found maternal and paternal effects in manifestation of some characteristics in hybrids are considered in connection with elucidation of inheritance type of morphological characters in acipenserids. The paternal effect observed by some characters in hybrids beluga × starred sturgeon is explained by prevalence of dominant alleles in the genome of starred sturgeon in comparison with beluga. The maternal effect is elucidated by a few characteristics related to parameters of the head, first of all to the volume of the brain region of skull. Evidently, in this case, the matrocliny depends on the fact that information on the number of segments of embryo and their position is determined by the maternal organism during oogenesis.

The comparative morphological study in different Acipenseriform species demonstrates that there are only two morphological features combining the kaluga and the great sturgeon and separating them from other sturgeons, namely the shape of a mouth and the manner attaching of gill membranes to isthmus in adult specimens; whereas many morphological characters are different in these species. The relations of morphological similarity/distinction among different sturgeon species and polyphyletic origin of genus Huso revealed by both molecular and cytogenetic studies presume the restoration of initial taxonomic states for the great sturgeon and kaluga as members of the same genus Acipenser, namely A. huso and A. dauricus.

Sturgeons and paddlefishes are frequently referred to as 'living fossils' among the actionpterygian lineage. They are increasingly facing threats to their existence because of various anthropogenic pressures. In this study, we present the complete mitogenome sequence of the Russian sturgeon Acipenser gueldenstaedtii (Acipenseriformes; Acipenseridae). The mitogenome showed highly homogeneous molecular features compared to previously known vertebrate mitogenomes. Phylogenetic tree inferred from concatenated protein-coding and tRNA genes unambiguously revealed the monophyly of A. gueldenstaedtii, Acipenser stellatus, and Huso huso. Genetic information of the endangered A. gueldenstaedtii will provide baseline data needed to develop molecular markers for stock identification and assessment of population diversity and also to develop future conservation strategies.

Sturgeon species in the Danube River basin have experienced severe decline. Besides overexploitation, habitat loss, and pollution, they are further endangered by lack of efficient policy and management, as well as by serious lack of knowledge about their life history. Although population viability analysis (PVA) could represent an extremely valuable tool to cope with these problems, it has not so far been applied to Danube populations. This paper represents an assess?ment of different PVA methods and models developed for sturgeon species. It analyzes their results, main advantages, drawbacks, and problems, and discusses the possibility of applying PVA to sturgeon populations in the Danube River basin.

This study focused on accumulation of organochlorine compounds (OCs), including dichloro-diphenyl-trichloroethanes (DDTs), hexachlorobenzene (HCB), hexachlorocyclohexanes (HCHs), and polychlorinated biphenyls (PCBs) accumulation in the muscle of four sturgeon (Persian sturgeon, Acipenser persicus; Stellate sturgeon, Acipenser stellatus; Ship sturgeon, Acipenser nudiventris and Beluga sturgeon, Huso huso) from the southern Caspian Sea. The DDT group was prominent in all of the sturgeon muscle tested constituting almost half or more of the total organochlorine content. Contaminant concentration generally followed this order: DDTs > PCBs > HCHs > HCB. The OCs concentrations in Beluga sturgeon (H. huso) were the highest and over four times higher than in the next highest species (A. nudiventris). From an ecotoxicological point of view, the concentrations of OCs in experimental fishes do not reflect a comparatively clean and pollution-free environment; however, results from this study shown that the inflow of organic pollutants into the Caspian Sea has been reduced when compared with prior studies. Levels of measured OCs in sturgeon were relatively low, but the level of some OCs in some of the specimens tested exceeded the guidelines for food; therefore, the maximum allowable daily consumption rate for sturgeon from this watershed may be limited by DDTs and PCBs content for high risk populations.

Ten microsatellitelociweretested on Mendelian seg-regationinthebester^hybridof beluga,HusohusoL.and sterlet, Acipenser ruthenus L. in the fourth gen-eration. All studied loci showed disomic inheritanceandMendeliansegregationof theiralleles.Themole-cularapproachbymicrosatelliteDNAanalysisrepre-sents a reliable tool for interspeci¢c characterizationofsturgeonsandtheirhybrids(diierentallelesofsev-eral lociare present in sturgeon ¢shes, and interspe-ci¢c hybrids posesses both maternal and paternalspeci¢c alleles).This is the ¢rst report of the Mende-lian segregationtesting in interspeci¢c hybrid of aci-penserid ¢shesusingmicrosatelliteDNA markers.Keywords: Acipenseridae, allele’s segregation,bester, hybrids,microsatellitesIntroductionAcipenseriformes are one of the most threatenedgroups of vertebrates. Almost all sturgeon popula-tionsarevulnerable, endangeredandsomeare near-ing extinction and they are listed under theConvention on International Trade in EndangeredSpecies of Wild Fauna and Flora (CITES). The maincauses of the decline of the stocks comprise contam-ination of water and sediments by pollutants, over-¢shing, degradation of habitat (damming or rivermodi¢cation). Therefore, all sturgeons are a speciesrequiring protection, which has resulted inthe closeregulation of the caviar trade and perhaps a tradebanonbelugacaviar(Birstein1993).Sturgeonsaresomeofthemostimportanteconomicspecies in the world because they are producers ofblack caviar. The high commercial value of blackcaviar has also resulted in the decline of all sturgeonpopulations. The decline of caviar ¢sheries in theCaspian Sea (Birstein 1993), coupled with the stronginternational demand of sturgeon meat and blackcaviar has created a potential market for farm stur-geonmeatandcaviar.Arti¢cialproductionofsturgeonmay be the solution to oiset the decreasing supply ofsturgeonproducts.Nowadays,arti¢cialbreedingtech-nologies including induced spawning, incubationandlarvae rearing are available for several sturgeon spe-cies. Farming technologies are well established inintensivesystemsforSiberiansturgeon(AcipenserbaeriBrandt), Russian sturgeon (Acipenser gueldenstaedtiBrandt) and sterlet (Acipenser ruthenus L.) in Poland(Kolman, Szczepkowski & Pyka 1997). Another solu-tion to produce food ¢sh was to use hybrids that pos-sessed the good characteristics of both the parents.One example is the ‘bester’, an intergeneric hybridmadebetweenthesterletmalethatlivesinfreshwater,and the beluga (Husohuso L.) female, whichgrows ra-pidlyand reaches a large size (Steiens, Jaehnichen &Fredrich 1990). The rearing technology for thishybrid was developed throughout the1960s in Russia(Chebanov & Billard 2001). Bester represents an im-portant economic resource for meat and black caviarproduction. Nearly 90% of the body weight of besteris a marketable product (Wedekind 2002).This hybridwas produced byarti¢ciallysupported breedingattheRussian ¢sh farms and then widely exported. Its kar-yotype stabilized after the third generation and a de-cline in progeny survival in the was reportedsuccessivegenerations(Arefjev&Nikolaev1991).Studies on inheritance of microsatellite loci insturgeons were conducted only in pure species, for

We describe a reliable method for the identification of the species source for caviar. The assay is based on the identification of diagnostic nucleotide positions in the mitochondrial cytochrome b gene from a sequence database of 20 of 25 living sturgeon species. The collection of attribute data is polymerase chain re- action (PCR)-based and can readily identify the character states of several diagnostic nucleotide positions in the cytochrome b gene for the three main commercial species of caviar-producing sturgeons ( Acipenser gueldenstaedtii , A. stellatus , Huso huso ). Over 20 individuals from each of the three species from a wide range of geographic regions were used to determine which of the potentially informative sites are diagnostic of phy- logenetic lineages through use of the population aggregation analysis method. We also report results from a survey of 95 lots of commercially available caviar in the New York City area. Overall, 23% of the designations made by caviar suppliers were mislabeled with respect to species identification. Recent declines in population size of the three commercial species, combined with an increase in the demand for caviar on the interna- tional market, could have caused the observed mislabeling. Replacement of commercial species with endan- gered and threatened species indicates possible illegal harvest and poaching; action should be initiated to en- sure the survival of all threatened Acipenseriformes. The use of our PCR assay might aid in conservation efforts in the United States and internationally.

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 genetic identification intravital tissue specimens, 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.

Summary Whereas reliable mtDNA-based methods for species identification of sturgeon caviar are at hand, the development of techniques to separate populations (stocks) or different sources (wild vs farmed) is presently at a preliminary state. We tested three methods, Differential Scanning Calorimetry, determination of stable isotopes (δ15N and δ13C), and mRNA analysis (reverse transcription polymerase chain reaction), for their diagnostic power for population and/or source identification of caviar. Farmed caviar (Acipenser baerii) from northern Germany and caviar samples presented by a trading company (Huso huso, Acipenser stellatus, Acipenser gueldenstadtii, Acipenser persicus from Iran and Kazakhstan) were included. Firstly, several DNA-based methods (single strand conformation polymorphism analysis, restriction fragment length polymorphism, sequence analysis) were used for species identification. Sequence analysis of cytb showed the largest diagnostic power. According to population and source identification issue, we conclude that all three methods have considerable potential. Nevertheless, additional methods like fatty acid profiling should be added for a reliable identification of populations and sources.

Summary As evolutionary relationships within the order Acipenseriformes are not well understood and some classifications are currently controversial, the study of evolutionary relationships, especially based on genetic data, has received much recent attention. In this reanalysis we present a nearly complete proposed phylogeny of the order, including 25 species, based on the maximum likelihood analysis of combined DNA sequence data (4406 base pairs) from five mitochondrial genes sequenced in our laboratories (cytochrome b, 12S rRNA, cytochrome c oxidase subunit II, tRNAAsp and tRNAPhe) and three mitochondrial gene regions sequenced by Birstein et al. (2002) (16S rRNA, NADH5 and control region). Examination of the molecular phylogeny using either maximum likelihood, Bayesian analysis, maximum parsimony or neighbor-joining leads to the following conclusions: (i) the two species of paddlefish do form a clade; (ii) the most basal position within the Acipenseridae remains unresolved, held either by the genus Scaphirhynchus or by the clade containing Acipenser oxyrinchus and A. sturio; (iii) Huso is not monophyletic, with the two species of Huso found embedded separately within the genus Acipenser; (iv) A. sinensis and A. dabryanus are confirmed as closely related; (v) the previously described Atlantic-Pacific subdivision within the Acipenser ⁄ Huso complex is supported and (vi) the unexpected placement of Pseudoscaphirhynchus kaufmanni within Acipenser is supported by this analysis. These results offer further evidence that some revision of acipenseriform classification may be needed to accurately inform conservation efforts and that future phylogenetic studies of this group should focus on the analysis of nuclear genes.

Summary We present an analysis of sequence variation across complete mitochondrial (mt) genomes of eleven sturgeon species. We have sequenced five mt-genomes from four Ponto-Caspian species: Acipenser gueldenstaedtii (Russian sturgeon), Acipenser persicus (Persian sturgeon), Acipenser naccarii (Adriatic sturgeon), and Acipenser baerii (Siberian sturgeon). Two specimens of A. gueldenstaedtii were included representing the gueldenstaedtii-like haplotype and the baerii-like haplotype. Phylogenetic information content of each gene, clusters of genes sharing similar functions (tRNAs, protein coding sequences) and of the entire mitochondrial DNA genome was evaluated using the Shimodaira and Hasegawa test. Based on their suitability to reconstruct sturgeon phylogeny, mitochondrial genes were ranked between very good (ND5, cytb – large agreement between phylogenies based on these genes and the phylogeny calculated on the entire mt genome), good (COI, ND4, ATP6), medium (ATP8, COII, COIII, ND1, ND2, ND3, ND4L) and weak (ND6 – tree topology is significantly deviated from the expected one). The maximum parsimony (MP) tree based on entire mt genomes showed that Scaphirinchus is a sister clade of the genera Acipencer and Huso. However, maximum likelihood (ML) algorithm with the most suitable nucleotide evolution model (GTR+I+G) places Scaphyrinchus within Acipenser as a sister branch to PontoCaspian species. Both algorithms (MP, ML) agreed in the following points: (i) Atlantic and Pacific species are separated in different clades, Huso huso is basal with the Atlantic species and (ii) all species of the gueldenstadetii-complex are closely related. Finally, eight substitutions between A. baerii and the baerii-like specimen of A. gueldenstaedtii were found overall protein coding sequences, and 131 substitutions were detected between the gueldenstaedtii-like and baerii-like haplotype over the entire mt genome. Taking the small sample size under consideration, these differences have to be handled with care and should be addressed in further studies.

Sturgeons had played an important role in the history of Hungarian fisheries, but over-fishing, followed by extensive river regulations and deterioration of habitat quality have caused a decrease in populations to the verge of extinction in the middle Danube and its tributaries. Stellate sturgeon (Acipenser stellatus) and great sturgeon (Huso huso) are practically vanished from the Hungarian waters and Russian sturgeon (A. gueldenstaedti) and ship sturgeon (A. nudiventris) have sporadic occurrence only, while Atlantic sturgeon (A. sturio) was never resident of this stretch of the Danube River. Sterlet (A. ruthenus) is the only common species caught for commercial and recreational purposes. The paper describes the past and recent status of the Middle Danubian sturgeon populations and emphasizes problems of restricted availability or lack of essential spawning and nursery habitats. Impacts of floods on sterlet population dynamics are demonstrated by long-term data of commercial fishery. Existing conservation measures, restocking and fishing regulations in Hungary are evaluated.

Summary In the past, sturgeons were practically unknown in Greece, both to the public and to scientists, the latter not having had the opportunity to study wild populations of the four native species. Populations of stellate sturgeon (Αcipenser stellatus Pallas, 1771), Adriatic sturgeon (Acipenser naccarii Bonaparte, 1836), and beluga sturgeon (Huso huso L., 1758) gradually collapsed by the end of the 1970s. Only the River Evros (Thrace, N.W. Greece) sustained a small fishery and caviar canning operation with European sturgeon (A. sturio L., 1758) until 1975. Collapse of stocks was mainly attributed to overfishing, pollution and damming. Sturgeons became widely known after initial farming efforts by the Municipal Hatchery at Lake Ioannina in 1992. Broodstock or fertilized eggs of species with high aquaculture potential, such as sterlet (Acipenser ruthenus L., 1758), Russian sturgeon (Acipenser gueldenstaedtii Brandt, 1833), bester hybrid (A. ruthenus ×H. huso), paddlefish (Polyodon spathula Walbaum, 1792), Siberian sturgeon (Acipenser baerii Brandt, 1869) and white sturgeon (Acipenser transmontanus Richardson, 1836) were imported into Greece between 1992 and 2004. Hatchery technology, larval rearing and production systems are reviewed in this paper and, despite problems, past and present efforts appear to meet a particular interest of the aquaculture sector as well as of those interested in the restoration of wild stocks.

Summary Brain anatomy and structure, composition of the neurons, and cytoarchitectural maps were compared between five species of Acipenser, one species of Huso and two species of Scaphirhynchus. Morphological differences in the forebrain structure between species and genera were apparent. The evolutionary history of the Acipenseridae has been marked by an extensive mosaic radiation in the evolutionary development of the inner structure of their brains. Members of Scaphirhynchus have a very simple telencephalon structure differing significantly from that of Huso and Acipenser. It is clear that neuromorphological variation of sturgeon species will serve as an additional data useful in understanding the evolutionary processes and history associated with the speciation in Acipenseridae.