Organization of diencephalon of the sturgeons. Posterior tubercular area. Caudal region

Cytoarchitectonics of caudal region of the posterior tubercular area of diencephalon was studied in four species of the true sturgeons: the giant sturgeon, Huso huso L., Kura sturgeon, Acipenser güldenstädtii persicus n. Kurensis Belyaeff, stellate sturgeon, Ac. stellatus Pall. and the barbel sturgeon Ac. nudiventris Lov. Morphologic organization of the brain region was studied by using staining techniques of Nissl and Bielschowski (Viktorov’s modification). Five nuclei were identified in the caudal region of the posterior tubercular area in all studied species: caudomedial, caudal and lateral thalamic nuclei forming the medial group, as well as lateral torus and posterior thalamic nuclei forming the lateral group. The latter two nuclei have their subdivisions. Characteristic peculiarity of the caudal region is the presence of only migrated nuclei. It is concluded that the level of differentiation of the diencephalon posterior tubercular area of the sturgeons allows considering it as one of the most evolutionary advanced structures among those in the actinopterygian fish line.     

Organization of diencephalon of the sturgeons. Dorsothalamic and epithalamic areas

Cytoarchitectonics of the dorsal part of diencephalon and epithalamus was studied in four species of the true sturgeons: the great sturgeon Huso huso L., the Kura sturgeon Acipenser gƅlden-st∂dtii persicus n. Kurensis Belyaeff, the starred sturgeon Ac. stellatus Pall., and the barbel sturgeon Ac. nudiventris Lov. Material was processed using routine Nissl and Bielschowski staining techniques (the latter in Viktorov’s modification). The described areas are the smallest among diencephalic regions. Dorsal thalamus is exceeded by the ventral one both in length and in the number nuclear structures. It includes four nuclear structures, three of which are periventricular: the anterior, posterior dorsal, and central nuclei, while the subhabenular nucleus is a migrated one. Epithalamic area has a pronounced right-left asymmetry that consists both in the external appearance of these structures and in their internal organization. Three types of neurons were revealed in epithalamic structures: granular cells, rounded neurons with poorly expressed processes, and bipolar neurons with clearly seen processes. In the epithalamic area, a sufficiently large nervous structure designated as the central habenular nucleus consisting of relatively large rounded neurons was described. A conclusion is made about a unique organization the studied areas in the true sturgeons, which distinguishes them markedly among both other actinopterygian fish and the higher organized vertebrates.     

Study on Localization of Hemopoietic Tissue in Sturgeon

Morphological and autoradiographic studies on various hemopoietic tissues in sturgeon are presented. The classic hemopoietic organs characteristic of lower vertebrates, such as the kidney and spleen, are studied as well as unique hemopoietic structures described only in the evolutionarily most ancient fish species (hemopoietic tissues of cartilaginous skull capsules and epicardium). The intensity of cell divisions in hemopoietic foci has been characterized by autoradiography. The results obtained provide a basis for the revision of traditional views about the phylogeny of hemopoiesis. They provide evidence that the osteogenic gravitation of hemopoietic tissue shows up in evolution alongside the appearance of the inner skeleton.     

Organization of diencephalon of the sturgeons. Posterior tubercular area. Periventricular and rostral parts

Cytoarchitectonics of periventricular and rostral parts of the posterior tubercular area of diencephalon was studied in four species of the cartilaginous ganoids by using routine Nissl staining and Bielschowski impregnation technique in Viktorov’s modification. The posterior tubercular area in the giant sturgeon Huso huso L., the Kura sturgeon Acipenser güldenstädtii persicus n. Kurensis Belyaeff, the stellate sturgeon Ac. stellatus Pall., and the barbel sturgeon Ac. nudiventris Lov. was shown to have similar structure. Six structures were identified in these areas: the periventricular nucleus, paraventricular organ, nucleus of the paraventricular organ, and posterior tuberal nucleus in the periventricular region and preglomerular medial and lateral nuclei in the rostral region. Both nuclei of the rostral zone are migrated nuclei. Out of nuclei of the posterior tubercle regions, the posterior tuberal and medial preglomerular nuclei are characterized by polymorphism of cellular elements. A conclusion is made that these parts of the posterior tubercular area in the sturgeons considered to be the lower ray-finned fish are comparable with those of the higher teleosts, and even are more differentiated according to some parameters.     

Age-Dependent Variation of Serum Protein Antigens in Sturgeons (Acipenseridae,Acipenseriformes)

We studied the variation of antigenic properties of proteins in two sturgeon species at different stages of postembryonic development. The deepest changes occurred in individual components of albumins and -globulins (transferrins) and were mostly related to an increased proportion of the protein accounting for these antigens. Transformation of the main component of albumins A1 into adult antigens was completed in 5-month old juveniles. The main component of -globulins A (component of transferrins) appeared in the blood flow much later than other proteins and could retain the juvenile features until the age of 3–4 years. Other antigens belonging to ₁- and ₂-globulins and the second component of transferrins were more stable and did not undergo substantial changes. The direction of ontogenetic variation of serum antigens in sturgeon juveniles did not depend on the habitat of adult fish in fresh or sea water.     

Projected lake sturgeon recovery in the Milwaukee River,Wisconsin, USA

Using a forward projecting population model, the timing and scale of Lake Sturgeon Acipenser fulvescens (LS) recovery and natural reproduction was estimated for the Milwaukee River in Wisconsin, USA for the years 2004–2048. LS, a widely distributed potamodromous Acipenseridae species in North America, have, like other sturgeon species, suffered population declines due to overharvest and other factors since the 1800s. LS recovery efforts were initiated in the early 1980s following the successful development of LS propagation techniques and stocking has become a widely utilized tool in LS recovery programs. Sturgeon recovery programs are long-term endeavors, with annual stocking usually planned for 25 plus years, along with population assessments and habitat improvements conducted over decades before project success can be verified. LS recovery activities on the Milwaukee River, a Lake Michigan tributary in southeast Wisconsin, began with barrier mitigation in 1997 and stocking in 2003. The modest size of the Milwaukee River, along with habitat improvements, and 17 years of stocking, provided an opportunity to model and predict LS population recovery trends. A forward projecting population model with an imbedded stochastic Ricker stock-recruitment relationship, adjusted for the estimated LS productive capacity of the Milwaukee River, estimated the timing and scale of LS recovery during 2004–2048 predicting a 18.3% annual average population rate of increase during the stocking period, and a 5.7% post-stocking rate. Accelerated LS growth and maturity due to goby consumption built into the model resulted in projections of gravid adult males present in 2012 and spawning adult females and natural recruitment in 2019. During the 2020 spawning period a group of adult-sized LS were observed in the Milwaukee River below an intermittent barrier on the river. The model predicted adult LS densities to grow from 22 in 2012 to 8088 in 2048, and annual natural recruitment to grow steadily from 76 yearlings in 2019 to an average of 4000 yearlings/year during 2039-2049. The estimated number of yearling recruits per spawning (gravid) female dropped steadily from 21 in 2019 to 8 recruits per gravid female in 2048 as a function of the Ricker stock-recruitment relationship built into the model. The model results indicate that significant LS recovery can possibly begin in a shorter time frame on Great Lakes tributaries than originally expected through systematic resolution of habitat issues and LS stocking. Results can also be used to help anticipate recovery trends, fine tune stocking and habitat strategies, and plan LS recovery assessments.     

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.     

Species and hybrid identification of sturgeon caviar: a new molecular approach to detect illegal trade

Overexploitation of wild populations due to the high economic value of caviar has driven sturgeons to near extinction. The high prices commanded by caviar on world markets have made it a magnet for illegal and fraudulent caviar trade, often involving low‐value farmed caviar being sold as top‐quality caviar. We present a new molecular approach for the identification of pure sturgeon species and hybrids that are among the most commercialized species in Europe and North America. Our test is based on the discovery of species‐specific single nucleotide polymorphisms (SNPs) in the ribosomal protein S7, supplemented with the Vimentin gene and the mitochondrial D‐loop. Test validations performed in 702 specimens of target and nontarget sturgeon species demonstrated a 100% identification success for Acipenser naccarii, A. fulvescens, A. stellatus, A. sinensis and A. transmontanus. In addition to species identification, our approach allows the identification of Bester and AL hybrids, two of the most economically important hybrids in the world, with 80% and 100% success, respectively. Moreover, the approach has the potential to identify many other existing sturgeon hybrids. The development of a standardized sturgeon identification tool will directly benefit trade law enforcement, providing the tools to monitor and regulate the legal trade of caviar and protect sturgeon stocks from illicit producers and traders, hence contributing to safeguarding this group of heavily threatened species.     

Organization of diencephalon of the sturgeons. External nuclei of the pretectal area

Cytoarchitectonics of the external nuclei of the pretectal area was studied in four species of the sturgeons: great sturgeon, Huso huso L., Kura sturgeon, Acipenser gueldenstaedtii persicus n. Kurensis Belyaeff, stellate sturgeon, Ac. stellatus Pall. and barbel sturgeon, Ac. nudiventris Lov. Study of morphological organization of the structures was carried out using routine Nissl staining and Bilschowski impregnation technique in Viktorov’s modification. Similar structure of this pretectal area was found in the species. Five nuclear formations were described in this pretectal area: parvocellular and magnocellular external pretectal nuclei, laminiform nucleus of pretectum, dorsal pretectal nucleus, and the accessory optic nucleus. Comparison of the obtained data with the literature revealed a high level of differentiation of the area of pretectum in the sturgeons. Also, a general conclusion is given on the organization of the whole pretectal area in the sturgeons.     

Sturgeon re‐introduction in the Upper and Middle Danube River Basin

All six sturgeon species naturally occurring in the Danube River from the Black Sea (BS) to the upstream reaches in Germany today are under severe pressure and classified as either vulnerable, critically endangered or already extinct in the Danube River Basin (DRB). This sharp decline of populations is the result of two major drivers: habitat alteration and unsustainable harvest. The Danube River Basin can be divided in three functionally separated sections by its hydromorphology and character: The Lower Danube (LD) and BS, now also separated ecologically from the Middle Danube (MD) by two hydropower stations at the Iron Gate gorge, 800 km from the sea, currently restricting the remaining anadromous sturgeon species (A. gueldenstaedtii, A. stellatus, Huso huso) to the LD and BS also restraining migrations of potamodromous species. The Upper Danube (UD) is nowadays disconnected from the approx. 850 km long MD by Gab?ikovo Dam. The UD itself, as well as many tributaries along the Danube, are fragmented by numerous barriers, leaving no more than a total of 300 km free flowing river out of 700 km. Overharvest led to disappearance of most sturgeon species in the UD already in the Middle Ages, with populations in the MD following in the subsequent centuries. Today the potamodromous sterlet (A. ruthenus) still exists in small decreasing populations in the UD and MD basins, where its occurrence is supported by stocking. Most probably the potamodromous ship sturgeon (A. nudiventris) is extirpated in the whole basin. The Danube basin comprises 19 countries, being the most international river basin in the world, rendering coordinated conservation efforts a challenge. Strategic guidelines for the conservation of the Danube sturgeons are available in form of several action plans, but implementation remains insufficient as of yet. This paper attempts an analysis of the potential for sturgeon restoration in the UD and MD basin and highlights the need for concerted approaches when it comes to ex situ actions and reintroductions.