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A comparative analysis of data on the morphological, genetic and ecological features of Russian, Persian and Colchic sturgeons was carried out in order to assess their taxonomic relations, diagnostic characteristics and distribution patterns in the Ponto-Caspian basin. The results confirmed the presence of two close related and morphologically similar species in the Caspian basin—Acipenser gueldenstaedtii and A. persicus, the reproductive isolation of which was proved by genetic data. The complex of diagnostic characters of these species includes, in addition to the traditionally accepted body color and the shape of the snout, several craniological indices: Pds/Ri and W/Ri. The Colchic sturgeon remains virtually unstudied from a genetic point of view. The results obtained allow us to consider it an independent subspecies – A. persicus colchicus. It differs from the Caspian Persian sturgeon, as well as from the Russian sturgeon with a longer snout and larger values of the craniological index B/Ri. The distribution of the Colchic sturgeon in the Black Sea basin requires further research.

This study provides biological, fishery, and production characteristic of spawning females of a triple hybrid between the Russian sturgeon, Siberian sturgeon, and Amur sturgeon (RS × SS) × AS and other commercial hybrid sturgeon forms grown in the cages of a warm-water fish farm in Primorsky Krai, Russia. The survival rate of larvae and juveniles of the triple hybrid in conditions of warm-water pools and the survival rate of marketable-size sturgeon was higher than those of Amur sturgeon and hybrids between the Russian and Siberian sturgeons. The weights of the triple hybrid individuals at an age of 3 and 4 years were 1.58 and 2.36 kg, respectively. These values were higher than those recorded for the hybrids between Russian and Siberian sturgeons and close to the standard values for Amur sturgeon. The fish productivity reached 94 kg/m2 of cage, or 134 kg/m2 of cage taking fish that were sold into account. The values of this index were much higher than the standard values not only for Amur sturgeon, but also for other sturgeon species and hybrids. Up to 93% of the females reached maturity after being treated with a hormone-stimulating drug. The first female of the triple hybrid sturgeon became mature at an age of 9 years with a body weight of 13.1 kg. Maturation of the other females of the same year-class was stretched in time and lasted for 7 years, up to 16 years of age. Approximately 75% of them reached maturity at an age of 10–12 years. The maximum recorded weight of a female triple hybrid was 29 kg at an age of 14 years. The inter-spawning interval for 97% of females was 1–2 years. The average annual yield of hard roe obtained from one female at an age of 9–16 years per spawning event was 2.28 kg; the weight of one egg was 17.6 mg; the fecundity was 132 000 eggs; the relative working fecundity was 7440 eggs/kg; the oosomatic index was 12.8%. The values of most of the production indices for the female triple hybrids were intermediate between those characteristic of the initial species used for crossbreeding. For three or four spawning seasons, an average of 5.25 kg of hard roe, or 30% of body weight, was obtained from one female triple hybrid. The roe yield from the most productive females was 10.8–11.0 kg, or 55–73% of body weight. The roe of the triple hybrid sturgeon was distinguished by high quality and was used for manufacturing food products. Females were technologically well adapted for roe stripping and showed a high survival rate of approximately 98% during long-term exploitation. Thus, the triple hybrid of the Russian, Siberian, and Amur sturgeons can be recommended for commercial cultivation with a high production output at warm-water sturgeon farms. Female triple hybrids can be used for the production of quite large amounts of high-quality food caviar. Their roe yield is lower than that in Amur sturgeon and does not differ significantly from the roe yield in the hybrid between the Russian and Siberian sturgeons.

The determination of the carnosine level in fish muscle tissues is helpful for the purposes of general biology and comparative muscle physiology of various fish species; it may be also useful for estimation of the nutritional value of fish products. The mass-spectrometric method of the determination of carnosine in muscle tissues has been improved and tested in this work. The carnosine levels in the muscles of the Russian sturgeon, Siberian sturgeon, sterlet, hybrid of sterlet and kaluga, hybrid of Siberian sturgeon and kaluga have been determined for the first time with this method. The starlet-and-kaluga hybrid, regardless of sex, contains 3.33 times more carnosine than the sterlet (p < 0.01). The female hybrid of Siberian sturgeon and kaluga contains 1.50 times less carnosine than the female Siberian sturgeon (p < 0.1). Since carnosine consumption is important for carnosine biosynthesis in human muscles, the hybridization of sterlet with kaluga is more efficient in terms of nutrition value than pure sterlet breeding, and the hybridization of Siberian sturgeon with kaluga is less effective than sturgeon breeding.

Cryopreservation of fish and amphibian eggs is still an unsolved problem. The formation of ice crystals inside and outside cells acts as a main detrimental factor during a deep freezing of fish eggs, as well as crystal growth (recrystallization and repeated crystallization). Designing efficient cryoprotective media is necessary in order to avoid egg injury from freezing. Additional components that are present in a cryoprotective medium and reduce the thermomechanical stress and cracks of frozen tissues might increase oocyte survival after freezing–thawing. Natural components of eggs and the ovarian fluid are promising as such additives. The formation of ice microparticles was studied in thin layers (0.2 mm) of the ovarian fluid and components of Russian sturgeon egg homogenates upon their cooling to a liquid nitrogen temperature (–196°C). The processes of freezing, ice cracking, and microparticle formation were observed as the temperature was decreased gradually. The shape and size of ice microparticles were found to depend on the composition of the freezing solution. Certain fractions of egg homogenate were assumed to be suitable as components of a cryoprotective medium.

This article discusses work on assessing the digestibility of a concentrate of Hermetia illucens larvae in fish with gastrointestinal digestion (rainbow trout Oncorhynchus mykiss, Russian sturgeon Acipenser gueldenstaedtii, red tilapia Oreochromis mosambicus × O. niloticus). It was found that this digestibility index of the larvae concentrate was 67–74%. At the same time, fish species consumed larvae protein at 91–97%, the digestibility of residual fat was 90–94%, and easily hydrolyzed carbohydrates amounted to 52–68%. Сhitin of H. illucens was digested 25–35% and did not adversely affect the digestion of protein and fat in the fish species studied. The digestion rates of the H. illucens larvae concentrate, protein, and easily digestible carbohydrates in O. mosambicus × O. niloticus are statistically significantly higher than in Onc. mykiss, while in A. gueldenstaedtii they were intermediate in comparison with tilapia and trout. This corresponded to the duration of food passage through the intestinal tract, which in O. mosambicus × O. niloticus, Ac. gueldenstaedtii, and O. mykiss came to 7.8, 9.6, and 15.7 hours, respectively. Fat and chitin were digested by red trout significantly more efficiently than other fish species. This corresponded to the duration of food passage through the intestinal tract, which for tilapia, sturgeon, and trout came to 7.8, 9.6, and 15.7 hours, respectively. The degree of digestibility of fat and chitin by trout was significantly higher than that of other fish species.

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.

—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.

The paper presents the results of the observations of the mass appearance of specimens of Siberian sturgeon (Acipenser baerii) in the Curonian Lagoon, released during an accident on a fish farm on the Grabova River in Poland. About 50 000 individuals of Siberian sturgeon and some Russian sturgeon (Acipenser gueldenstaedtii) entered the Baltic Sea. In 36 days, the first Siberian sturgeon individual was caught in the Curonian Lagoon. From the end of October the catches of sturgeon became mass in the Curonian Lagoon. The last sturgeon was caught on November 23, 2017. The volunteers managed to trace 27 catches of Siberian sturgeon. The area near the mouth of the Neman River was where the majority of catches occurred. It is possible that Siberian sturgeon may appear in the Neman River.

To study the role of somatotropin (ST) in osmotic regulation of anadromous acipenserids, the dynamics of hormone concentration in blood serum of juvenile Russian sturgeon Acipenser gueldenstaedtii Brandt (age 4 months, average length 16.9 cm, average weight 17.1 g) during fish adaptation to hyperosmotic medium of 12.5‰ salinity (403 mOsm/l) was evaluated for the first time. During the first 24 h after the transfer of fish from freshwater to hyperosmotic medium, an increase of ST serum concentration (up to 2.06 ± 0.09 vs. 0.98 ± 0.03 pg/ml in control fish from freshwater) was observed. This increase occurs concurrently with an increase in blood serum osmolarity (up to 386.2 ± 4.0 mOsm/l vs. 218.5 ± 4.9 mOsm/l in control) resulting from the diffusion of water from the organism under new osmotic gradient, as well as with the period of morphofunctional remodelling of the osmoregulatory system corresponding to the transition of fish to hypoosmotic regulation. 24 h after the start of the experiment, fish that have shifted to hypoosmotic regulation display the adaptive decrease in osmolarity (aimed at maintaining the relative constancy of blood serum) and the ST concentration (down to 1.18 ± 0.16 pg/ml after 120 h, comparable with that in the control fish). It is concluded that during transition of juvenile Russian sturgeon to hypoosmotic regulation, ST becomes involved in morphofunctional remodelling of the osmoregulatory system concurrently with other components of this system. ST-immunopositive cells were revealed in the dorsal part of mesoadenohypophysis of Russian sturgeon juveniles by immunochemical method.

Polysubstituted derivatives of sterically hindered phenol were found to reduce accumulation of hydroperoxides in the lipid extract from fish feed after 8-week incubation. Feeding of juvenile Russian sturgeon with fish food containing these compounds showed no negative effect on hydrobionts. Both in vivo and in vitro experiments revealed inhibition of hepatic lipid oxidation in juvenile Russian sturgeon in the presence of new bis-pyrrolidine derivatives of 2,6-di-tert-butylphenol. A reliable positive correlation was observed between the concentration of hydroperoxides in the lipid extract from fish feed and accumulation level of secondary enzymatic oxidation products of hepatic lipids in hydrobionts.

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.

For the first time by the example of juveniles of Russian sturgeon Acipenser gueldenstaedtii Brandt, the role of growth hormone of hypophysis in the osmotic regulation of acipenserids was studied, also the process of transformation of reserve chloride was described. In Russian sturgeon juveniles, administration of growth hormone of carp Cyprinus carpio at a dose of 1 mg per 1 g body weight causes changes in the fine structure of numerous reserve (undifferentiated) gill epithelial cells and thus stimulates their transformation into mature chloride cells involved in transport of monovalent ions. Increase in the number of chloride cells, on account of reserve cells, was accompanied by higher enzymatic activity of Na+/K+-ATPase in gill homogenates of the injected fish adapting to a hyperosmotic environment of salinity 12.5‰ (403 mosm/l) than in the intact fish under the same conditions but without hormonal treatment. Morphophysiological changes observed in the injected juveniles provided the more efficient dynamics of blood serum osmolarity under saline exposure than that in the intact fish. Their serum osmolality during the maximum rise (24 hours after the transfer of fish into the water of 12.5‰ salinity) was lower (p

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 structure of the pronephros in Russian sturgeon larvae, Acipenser gueldenstaedtii Brandt, at different stages of early postembryonic development (from hatching till 14 days old), was studied with histological and electron microscopy methods. The formed pronephros is represented by a system of bilaterally located pronephric tubules and an external single glomus, which is not integrated directly into pronephric tubules and is located in closed pronephric chamber. The glomus is positioned below the dorsal aorta and is vascularized by its capillaries. The thin structure of the glomus has the same characteristic features that are typical of and needed for the functions of any filtering organ. By the time when larvae transfer fully to exogenous feeding, the pronephros undergoes significant degradation and it is replaced by the mesonephric kidney which develops during the period of function of the pronephros. The peculiarities of the pronephros in acipenserids are discussed comparatively with the same organ in teleosts and amphibians.

This paper considers nonlinear effects in the dynamics of biological models. We describe two dynamic systems elaborated for simulating populations of Russian sturgeon and stellate sturgeon and based on formalization of the relationship between the spawning stock and recruitment according to the analysis of observational data. For the numerical study of differential equations with a structurally changing right-hand side, we use the method of representing models based on maps of states with conditional transitions. For dynamic systems, the presence of qualitatively different modes of the behavior of trajectories is revealed: stable periodic oscillations (sturgeon model) and unstable chaotic oscillations (stellate model) realized in a limited time interval due to a chaotic subset not being an attractor, which is present in the phase space.

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

The results are presented that have been obtained during long-term studies (1991–2009) on the efficiency of natural reproduction of the beluga, Russian sturgeon, stellate sturgeon, and sterlet in different spawning zones of the Volga. The influence of major environmental factors on the formation of the offspring of these fishes is analyzed. It is shown that the productivity of Volga spawning grounds varies depending on the river flow volume during spring floods and the abundance of active spawners. Practical recommendations are proposed for enhancing sturgeon reproduction in the Volga.

Hiemal and vernal forms of Russian Sturgeon Aci� penser gueldenstaedtii (Barannikova, 1975) migrating to the Volga to spawn with a different state of sex glands are described in its VolgaCaspian population. The relatively scanty vernal form and more numerous hiemal sturgeon, whose migration continues from ver� nal to autumn, are usually distinguished. The sum� mermigrant hiemal sturgeon is the farthest from maturity at the beginning of the river period of anadro� mous migration, and the autumnmigrant hiemal sturgeon goes into the river with more mature sex products. The vernal sturgeon migrates into the river in a state close to maturity in vernal and, after it is kept for a short period at fish hatcheries, mature sex cells are obtained from it with the help of hormonal injections. High basophilic cells that are close to the completion of the secretory cycle and are gonadotropes dominate in the distal pituitary lobe of these sturgeons, mainly in the ventral zone. The analysis of the ultrastructure has shown the presence of dark and light cells rich in the secretion as well as pictures of exhaustion of separate gonadotropes (Barannikova et al., 1984).

It was established that, as in many other representatives of Teleostei, there is a pheromonal regulation of reproductive behavior in Acipenseridae. The postovulatory releasing sex pheromone in Russian sturgeon Acipenser gueldenstaedtii, Persian sturgeon A. persicus, and starred sturgeon A. stellatus is in the ovarian fluid of females, whose odor has an interspecific efficiency and causes manifestation of typical spawning behavior (increase in locomotor activity, attraction to the site of solution presentation, circular swimming, and slightly convulsive movements) in mature males of its own and closely related species. A relationship was found between the ability of males injected with suspension of acetonized hypotheses of acipenserids to respond to odor of ovarian fluid and by both quality and quantity of sperm obtained from them. Data obtained extend our concepts of the role of chemical reception in biology of acipenserids and the range of their chemocommunications.

Dispermic androgenesis was used to produce, for the first time, an androgenetic progeny of the Siberian sturgeon (Acipenser baerii) and the androgenetic nucleo-cytoplasmic hybrids (Siberian sturgeon, A. baerii × Russian sturgeon, A. gueldenstaedtii) using cryopreserved sperm. Microsatellite DNA analysis confirmed exclusively paternal inheritance in the androgenetic progeny of Siberian sturgeon. Heterozygotes for certain microsatellite loci were detected among the androgenetic hybrids, thereby confirming a dispermic nature of androgenesis. According to the data of comparative morphological analysis, the obtained androgenetic hybrid, by the age of 15 months old, was completely identical to the paternal species. Both a female and a male were detected in the androgenetic sturgeon progenies, which is of interest for producing bisexual progenies via androgenesis. The data of this study confirm the feasibility of dispermic androgenesis using cryopreserved sperm to preserve and recover the gene pools of endangered sturgeon species.

The generative and somatic characteristics of female sturgeon of five species and three hybrid forms, which were reared at the TINRO Center’s warm-water cage farm at the north of Primorsky Krai and used in caviar production, are considered. Data on the somatic growth, roe output, functional fecundity, mean egg weight, and gonadosomatic index of the female Amur Sturgeon, Kaluga, Siberian Sturgeon of the Lena and the Baikal populations, Sterlet of the Volga population, hybrids of Russian Sturgeon and Siberian Sturgeon, hybrids of Siberian Sturgeon and Amur Sturgeon, and hybrids of Kaluga and Amur Sturgeon are analyzed. The sexual maturity age and interspawning intervals are defined in the studied females. Domesticated females of all the species are shown to mature a few years earlier than those in natural conditions and to have a greater body weight. The interspawning intervals shorten by a few years in domesticated females. Most female Sterlet and some females from both populations of Siberian Sturgeon spawn annually, while the remainder spawn once in 2 years. The interspawning intervals in two species of sturgeon that inhabit the Amur River and in hybrid forms usually last for 2 years. With age, values of characteristics such as roe amount, fecundity, mean egg weight, and roe output relative to body weight grow in females spawning for the second time in the warm-water farm. The maximum roe output is found in female Kalugas at the second spawning. Then the species follow in the order of decreasing of roe output: Amur Sturgeon, hybrids of Amur Sturgeon with Kaluga, hybrids of Siberian Sturgeon with Amur Sturgeon, hybrids of Russian Sturgeon with Siberian Sturgeon, Siberian Sturgeon of the Baikal population, Siberian Sturgeon of the Lena population, and Sterlet. The hybrid between the Russian Sturgeon and Siberian Sturgeon shows the best processability and survivability characteristics; the Amur Sturgeon and Sterlet follow.

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.

Analysis of electrophoregrams of water-soluble proteins of white skeletal muscle of 10 species belonging to three genera of the Acipenseridae family has allowed revealing an earlier not described system that can serve as a biochemical marker. This protein system represents a set of five fractions (A, B, C, D, E). A part of the studied species is monomorphous for one of these fractions (sterlet, giant sturgeon, Caspian sturgeon, and Amu-Darya shovelnose had phenotype A, barbel sturgeon—phenotype C, Amur sturgeon—phenotype D). In all individuals of the Amur sturgeon the identical three-component specter (phenotype ACE) was revealed. In the Sakhalin, Siberian, and Russian sturgeons a clearly expressed polymorphism was observed. Among the studied species the Russian sturgeon was characterized by the highest degree of heterogeneity and polymorphism. In the studied sample of this species all five protein variants are found, whereas in the rest of them—only a part of this set.

Three populations (Azov, Caspian, and Black Sea) of Russian sturgeon Acipenser queldenstaedtii were tested for polymorphism at nuclear (RAPD and microsatellites) and mitochondrial (PCR identification of two mitotypes) markers. In addition, morphometric analysis of he representatives of Azov population was carried out. According to the morphological characters, the Black Sea population occupied an intermediate position between the Caspian and Azov populations, reflecting the phylogeography of this species. In agreement with the morphometric data, genetic distances (the data of STR analysis) also placed the Black Sea population between the Caspian and Azov populations (FST = 0.058 and 0.043). The genetic distance between the Azov and Caspian population was somewhat higher (FST = 0.070). The highest allelic polymorphism at four microsatellite loci was found observed in Caspian population, while the lowest polymorphism was in the Sea of Azov. RAPD analysis distinguished high polymorphism within the populations, although it was not feasible for interpopulation analysis. Using the method differentiating the “baerii-like” and typical “gueldenstaedtii” mitotypes, the absence of the “baerii-like” marker in the Black Sea population was demonstrated. The frequency of this marker in Caspian and Azov populations constituted 31.1 and 1.8%, respectively. Possible evolutionary reasons for the interpopulation differences observed are discussed.

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.

Physiologobiochemical indices of males and females of the hiemal form of the Russian sturgeon Acipenser gueldenstaedtii of the summer and autumn periods of migration to the Volga after a prolonged holding (6–12 months) in the lower reaches of the river were determined. The possibility of gonad development and maturation after hormonal stimulation at a complete absence of the river period of migration and exogenous feeding was confirmed. In this period, regular changes in the concentrations of androgens, protein, glucose, and cholesterol in the blood serum that provide the necessary level of metabolism and testify to a high adaptation flexibility of these fish take place.

Taste preferences towards 20 free amino acids (L-isomers, 0.1–0.0001 M) were determined in juveniles of Persian sturgeon Acipenser persicus. It was found that most amino acids (16) had a positive effect on extraoral gustatory reception (increased the frequency of catching artificial pellets by fishes). The most efficient amino acids were the following: threonine, histidine, arginine, asparagine, phenylalanine, cysteine, glutamine, and glycine. Fifteen amino acids were efficient for intraoral gustatory receptors: serine, arginine, cysteine, histidine, alanine, and some others. The presence of these amino acids in pellets increased the consumption. Amino acids decreasing the frequency of catching or consumption of pellets were not found. Highly significant positive correlation was found between the amino acid ranges mediated by the extraoral and intraoral gustatory reception. The fishes demonstrated maximum sensitivity to aspartic acid, 0.01 and 0.001 M, respectively, for intraoral and extraoral gustatory systems. The threshold concentrations of arginine and glycine were higher for the intraoral gustatory system (0.01 M) than for the extraoral one (0.1 M). The comparison of Persian sturgeon with sturgeon fishes (Russian sturgeon A. gueldenstaedtii, Siberian sturgeon A, baerii, and starred sturgeon A. stellatus) studied earlier confirmed high species specificity of intraoral taste preferences in representatives of Acipenser genus. Species specificity of extraoral taste ranges was less pronounced.

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.

Cytoarchitectonics of periventricular and central nuclei of the pretectal area was studied in four species of the sturgeons: the great sturgeon Huso huso, L., the Russian sturgeon Acipenser gъldenst∂dti persicus n. kurensis, Belyaeff, the starred sturgeon Ac. stellatus, Pall., and the barbel sturgeon Ac. nudiventris, Lov.; this pretectum part has a similar structure. Study of these parts of the pretectal area was carried out by methods of Nissl and Bielshowskii modified by Viktorov. In this part of the pretectal area, nine nuclear structures were described, eight of them—nuclear; these are ventral periventricular pretectal nucleus and its dorsal component, dorsal periventricular pretectal nucleus, nucleus of medial longitudinal bundle, subcomissural organ, medial and lateral intercalate nuclei, and central and posterior pretectal nuclei. The main attention has been paid to the issue of the evolutional progression of this part of the pretectal area in the sturgeons as compared with other Actinopterygii.

A comparative analysis of stability of the hemoglobin structural-functional organization to effect of some experimental factors modeling action of internal medium and habitat was performed in representatives of Chondrostei and Teleostei belonging to euryhaline and diadromous fish. Differentiation of hemoglobins by stability parameters was shown to coincide to division of the studied fish into two main ecological groups: euryhaline fish with unstable hemoglobin and diadromous fishes with stable hemoglobin. In turn, the euryhaline fish by the character of destruction of hemoglobins under effects of destabilizing factors are differentiated into three subgroups: cartilaginous fish, cartilaginous ganoids, and bony fish. Thus, differentiation of hemoglobins by parameters of resistance to destabilizing factors is determined by peculiarities of the fish mode of life and is of adaptive nature. The described in the present study method of determination of critical precipitation concentration (CPC) of hemoglobin may be used as an express-method for estimation of hemoglobin resistance to salt effects, while the CPC values—as one of criteria of fish belonging to various ecological groups (diadromous, euryhaline).

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.

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.