Development of mesonephros in prolarvae of acipenserids (acipenseridae)

Development of the excretory system in early ontogenesis of acipenserids—the Russian sturgeon Acipenser gueldenstaedtii, the starred sturgeon A. stellatus, the sterlet A. ruthenus, and the great sturgeon Huso huso—is investigated histologically. In acipenserids, the mesonephros develops after hatching. At the 36th stage of development (after Detlaf et al., 1981), the mesonephros is a consecutively arranged group of spherical rudiments of placodes situated along the Wolffian duct. Morphological differentiation of mesonephros as the first generations of renal corpuscles, vascular glomeruli, and convoluted tubules is completed up to the 45th stage, i.e., to the moment of transition of prolarvae to active feeding.     

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.     

Inheritance of some quantitative morphological characters in reciprocal hybrids of starred sturgeon <Emphasis Type="Italic">Acipenser stellatus</Emphasis>and beluga <Emphasis Type="Italic">A. huso</Emphasis> (Acipenseridae)

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.     

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

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

Observations on the morphology of Truttaedacnitis clitellarius and T. lebedevi (Nematoda: Cucullanidae) from acipenserids and synonymy of the two species

Truttaedacnitis clitellarius (Ward & Magath, 1917) (Nematoda: Cucullanidae) is redescribed from the lake sturgeon Acipenser fulvescens from North America and compared with T. lebedevi (Skrjabina, 1966) from the Siberian sturgeon A. baeri. Studies on the morphology and morphometrics of the two species reveal considerable overlap with unique shared characters, such as the previously unreported position of the excretory pore at the level of the pseudobuccal capsule and arrangement of caudal papillae. This position of the excretory pore is anteriormost among all cucullanids. Although there is a trend towards smaller size of body and spicules in T. lebedevi, this reflects a long period of geographical separation and likely accounts for the minor morphological variations noted. Consequently, the two species are synonymised. The presence of one species of Truttaedacnitis, T. clitellarius, specific to freshwater acipenserids in North America and Siberia, suggests an ancient origin and slow rate of evolution for this cucullanid.     

The primary localization of ascorbate and its synthesis in the kidneys of acipenserid (Chondrostei) and teleost (Teleostei) fishes

The kidneys of the rainbow trout Oncorhynchus mykiss, the channel catfish Ictalurus punctatus (both Teleostei), and the white sturgeon, Acipenser transmontanus (Chondrostei) displayed similar profiles of ascorbate distribution irrespective of the capability of synthesizing ascorbic acid. The head kidney was found to be the richest in ascorbate, whereas the trunk kidney showed significantly lower ascorbate levels in all three species. The head kidney richness in ascorbate was correlated with the localization of the cortical and chromaffin tissues known to accumulate ascorbate in some fish and mammals. Based on ascorbate concentration, it was possible to distinguish the head from the trunk kidney in salmonids and sturgeons which have an antero-posterior-fused kidney. The absence of l-gulonolactone oxidase activity in the kidneys of the channel catfish and the rainbow trout was asserted biochemically. We also confirmed that the ascorbic acid-synthesizing enzyme exists in white sturgeon kidney, and found that the enzyme distribution was inversely correlated with ascorbate concentrations. An active transport of ascorbate might exist in the head kidney of both acipenserids and the teleosts in order to maintain this vitamin at high concentrations. This report suggests a link between ascorbate concentration and its physiological functions in kidneys of lower vertebrates.Abbreviations AA ascorbic acid - TAA total ascorbic acid - DHA dehydroascorbic acid - DCIP dichloroindophenol - EDTA ethylenediaminetetra-acetic acid - GLO l-gulonolactone oxidase     

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.     

The historical biogeography of sturgeons (Osteichthyes: Acipenseridae): a synthesis of phylogenetics, palaeontology and palaeogeography

Abstract. The historical biogeography of sturgeons is explored using information from palaeogeography, palaeontology and phylogenetic interrelationships. The integration of information from these diverse sources indicates that sturgeons reached a wide Laurasian distribution in the Cretaceous and Tertiary by freshwater and coastal dispersal routes across land connections and along newly forming continental margins. The fossil record also suggests a considerable degree of morphological stasis and also supports an estuarine habit, and perhaps diadromy, as an old and conserved life history trait. While a ‘centre of origin’ for sturgeons remains elusive, phylogenetic relationships indicate that diversification appears to have been associated with fragmentation of biota, and of landmasses and basins, by late Tertiary geological and climatic phenomena, such as orogeny and unequal glaciation over North America, the desiccation of central Asia and alteration of its drainages, and the formation of discrete Ponto-Caspian basins by the fragmentation of the Paratethys. Amphi-oceanic distributions of certain species (Acipenser medirostris Ayres) and sister taxa (e.g. A. oxyrhynchus Mitchill and A. sturio L.) are explained by coastal dispersal and subsequent vicariance by geological (sea-floor spreading and development of new continental margins) and climatic (Pliocene cooling) changes during the Tertiary. An hypothesis is developed for the relationships of the North American sturgeons and their potential relationships with the Siberian sturgeon A. baeri. Late Tertiary climatic and geological phenomena are hypothesized as mediators of vicariance and subsequent diversification of these acipenserids. It appears that although acipenserids are a geologically old group, the historical biogeography of surviving lineages is best explained by more recent geological and climatic changes.     

A Noninvasive Technique for Determining Sex of Live Adult North American Sturgeons

We have developed a noninvasive technique to determine the sex of adult North American sturgeon by examination of the external morphology of live individuals. We analyzed four sturgeon species taken by commercial and scientific harvest: white Acipenser transmontanus, green A. medirostris, Atlantic A. oxyrinchus and shortnose A. brevirostrum. Males have a urogenital opening in the shape of a letter Y, while the opening of females is in the shape of the letter O. We accurately sexed 26 of 36 sturgeon using this criterion. Accuracy was highest in live fish (82%), and significantly lower in dead fish (29%). Dead sturgeon usually have the rectum prolapsed so that the urogenital opening is protruded, and thus making the sexes indistinguishable.     

The use of microsatellite loci for identification of sturgeon species (Acipenseridae) and hybrid forms

The genetic polymorphism of ten sturgeon species that inhabit the territory of the Russian Federation (Russian sturgeon, Siberian sturgeon, Amur sturgeon, Sakhalin sturgeon, Persian sturgeon, ship sturgeon, sterlet, stellate sturgeon, beluga, and kaluga) was examined at five microsatellite loci (Afug41, Afug51, An20, AoxD161, AoxD165) (in total, 3821 individuals). The examined loci were successfully amplified with the same primer set in all species tested and demonstrated a high level of variation. Alleles specific to different species have been identified, which allows them to be used to identify species of sturgeon and their food products. In addition, the possibility of identifying hybrid forms was demonstrated. The assignment test performed in the STRUCTURE software program showed a high probability of correctly assigning each individual to its species based on genotyping with five microsatellite loci examined (96–98%, on average). However, for Russian and Persian sturgeon, the rate of proper species assignment was considerably lower (75 and 84%, respectively).

     

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.     

Can juvenile Baltic sturgeon (Acipenser oxyrinchus) smell the enemy?

Atlantic sturgeon (Acipenser oxyrinchus), also known as Baltic sturgeon, is considered extinct in German waters. Fish‐rearing for conservation purposes largely relies on classical hatchery technology focusing on traits like survival and growth in captivity but rarely focusing on subsequent life in the wild, lacking skills such as foraging or anti‐predation behavior. Predation is hence a major factor for mortality in newly stocked individuals. The aim of this study was to evaluate if naïve Baltic sturgeon juveniles were able to recognize a common predator—zander (Sander lucioperca)—by olfactory cues and adapt accordingly. Over a period of 30 days, Baltic sturgeons were supplied with effluent water from a rearing tank with zander (zander unit) and, as a control, carp (carp unit), three tanks each. Distribution within the tank, morphology of the dorsal scutes, stress (glucose, lactate and cortisol) and gene expression of brain plasticity and cognition were studied in comparison to the control group (carp unit). No significant differences between the zander and the carp unit were observed in any of the parameters measured. Thus, we conclude that naïve Baltic sturgeon is not able to innately recognize potential predators by olfaction alone. Therefore, future studies should focus on applying predator odor together with chemical alarm substances.     

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.     

Vulnerability of Young White Sturgeon, Acipenser transmontanus, to Predation in the Presence of Alternative Prey

Synopsis We conducted laboratory trials to test the vulnerability of young white sturgeon, Acipenser transmontanus, to predation when an alternative prey was available. In trials with two species of predators, we observed two feeding patterns. When equal numbers of white sturgeon and goldfish, Carassius auratus, were available, prickly sculpins, Cottus asper, ingested more white sturgeon. Conversely, northern pikeminnow, Ptychocheilus oregonensis, ate more juvenile coho salmon, Oncorhynchus kisutch, than white sturgeon in three out of four sets of trials, but ate more white sturgeon in one set of trials. White sturgeon size and the availability of cover did not affect the proportions of prey species ingested. Our results indicate that predation may be affecting survival of white sturgeon larvae and juveniles in the wild and could be one factor limiting recruitment of young-of-the-year white sturgeon in some locations.     

Triple hybrids obtained by artificial hybridization of the Russian sturgeon Acipenser gueldenstaedtii with the hybrid of the starred sturgeon A. stellatus and the great sturgeon A. huso (Acipenseridae): The kind of inheritance of some morphological characters and fertility of the parental hybrid form

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.     

Interspecific hybridization in natural sturgeon populations of the Eastern Black Sea: the consequence of drastic population decline?

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.

     

Patterns of sugar feeding and host plant preferences in adult males of An. gambiae (Diptera: Culicidae)

Sugar feeding by male mosquitoes is critical for their success in mating competition . However, the facets of sugar source finding under natural conditions remain unknown. Here, evidence obtained in Western Burkina Faso indicated that the distribution of An. gambiae s.s. (M and S molecular forms) males across different peri‐domestic habitats is dependent on the availability of potential sugar sources from which they obtain more favorable sites for feeding or resting. Among field‐collected anophelines, a higher proportion of specimens containing fructose were found on flowering Mangifera indica (Anacardiaceae), Dolonix regia (Fabaceae), Thevetia neriifolia (Apocynaceae), Senna siamea, and Cassia sieberiana (both Fabaceae) compared to that recorded on other nearby plants, suggesting that some plants are favored for use as a sugar source over others. Y‐tube olfactometer assays with newly‐emerged An. gambiae s.s. exposed to odors from individual plants and some combinations thereof showed that males use odor cues to guide their preference. The number of sugar‐positive males was variable in a no‐choice cage assay, consistent with the olfactory response patterns towards corresponding odor stimuli. T hese experiments provide the first evidence both in field and laboratory conditions for previously unstudied interactions between males of An. gambiae and natural sugar sources.     

The Holocene occurrence of Acipenser spp. in the southern North Sea: the archaeological record

Archaeological sturgeon remains from the southern North Sea basin used to be automatically attributed to Acipenser sturio, since this was the only acipenserid species believed to occur there. These species identifications, however, were in need of revision after a growing number of indications were found for the historical presence of Acipenser oxyrinchus in western Europe. In this study, morphological and genetic data on sturgeon remains from archaeological sites along the southern North Sea are revised. A large number of Dutch, Belgian, British and some French archaeological sturgeon remains, dating from the Mesolithic up to Late Modern times, are morphologically examined and fish sizes are reconstructed. This study of >7000 acipenserid bones proves the sympatric occurrence of European sturgeon A. sturio and Atlantic sturgeon A. oxyrinchus in the southern North Sea at least since the Neolithic (fourth millennium BC onwards), with A. oxyrinchus remains always outnumbering those of A. sturio. Human influence is documented by the decrease in finds through time, but no clear evidence was found for a diachronic change in fish lengths that could possibly be related to fishing pressure.     

Morphology, chemical contents and physiology of chondrostean fish sperm: a comparative study between Siberian sturgeon (Acipenser baerii) and sterlet (Acipenser ruthenus)

The present study was carried out with two sturgeon species, Siberian sturgeon (Acipenser baerii) and sterlet (A. ruthenus) to compare spermatological parameters to better understand inter‐species differences. Significant differences between morphometric features were observed such as acrosome length, acrosome width, head length, midpiece width and flagellar length, while midpiece length did not reveal such differences. The sterlet has a shorter spermatozoon than the Siberian sturgeon. Ultrastructural parameters vary significantly in terms of length of the nucleus, diameter of the endonuclear canals (EC), size of posterolateral projections (PP) and diameter of flagellum. Mean values for density of spermatozoa in the semen, seminal plasma pH, osmolality (mOsmol kg^?1), along with Ca²⁺, Na⁺, K⁺, Cl^? ions concentrations (mm ) were determined to be 0.61 ± 0.37 × 10⁹, 8.16 ± 0.18, 77.20 ± 52.28, 0.24 ± 0.06, 31.39 ± 10.21, 3.51 ± 1.10, 14.00 ± 4.30 in A. baerii and 0.41 ± 0.32 × 10⁹, 8.13 ± 0.19, 50.74 ± 6.27, 0.16 ± 0.11, 20.11 ± 3.78, 1.26 ± 0.54, 6.11 ± 0.60 in A. ruthenus, respectively. Significant differences were observed in Na⁺, K⁺ and Cl^? concentrations in the seminal plasma as well as in sperm velocity. The percentage of motile spermatozoa did not show any significant difference between the two species. Comparing the results of this study with published literature data on sturgeon spermatozoa reveals that morphological and ultrastructural parameters of spermatozoa together with some parameters of the seminal fluid and spermatozoa velocity can be used in comparative spermatology to better understand inter‐species differences. The observed biochemical and physiological differences should be also considered for the development of methods for controlled reproduction and for sperm cryopreservation techniques.     

Comparison of karyotypes of <Emphasis Type="Italic">Acipenser oxyrinchus</Emphasis> and <Emphasis Type="Italic">A. sturio</Emphasis> by chromosome banding and fluorescent in situ hybridization

A highly debated problem in Acipenseridae taxonomy is whether Acipenser oxyrinchus (North American Atlantic sturgeon) and A. sturio (European Atlantic sturgeon) are true species: a detailed comparison of their karyotypes could provide relevant information. Here we describe for the first time the karyotype of A. oxyrinchus (2n = 121 ± 3), and its features, among which the constitutive heterochromatin, revealed by C-banding technique, the distribution of telomeric regions, and the 5S rRNA genes, detected by FISH. The results reveal that A. oxyrinchus and A. sturio karyotypes and features are quite similar. Moreover, comparing the results obtained through hybridization by FISH with HindIII and PstI satellite DNA in these and in other sturgeon species, no hybridization signals are detected in A. sturio and A. oxyrinchus, while A. stellatus and A. gueldenstaedtii show hybridization. Thus A. sturio and A. oxyrinchus appear very similar from a cytogenetic point of view: these and molecular data repeatedly point out that A. sturio and A. oxyrinchus represent a sister clade in comparison to all other sturgeon species up to now studied.