Age-related variability of serum protein antigens in sturgeons (Acipenseridae, Acipenseriformes)

We studied the variability 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 beta-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 fry. The main component of beta-globulins A (component of transferrins) appeared in the blood flow much later than other proteins and could retain the fry features until the age of 3-4 years. Other antigens belonging to alpha1- and alpha2-globulins and the second component of transferrins were more stable and did not undergo substantial changes. The direction of ontogenetic variability of serum antigens in sturgeon fry did not depend on the habitat of adult fish in fresh or sea water.     

Heterogeneity and Polymorphism of Functionally Specialized Blood Proteins of Migratory Fish on the Example of the North Caspian Population of Russian Sturgeons during the Sea and River Periods of Life. 2. Hemoglobins

We carried out comparative studies of the heterogeneity and polymorphism of the most important functionally specialized blood proteins, hemoglobins. The fractional composition of hemoglobin proved to be identical during the sea and river periods of life for all main parameters (number of components, relative mobility, and protein content of each component). This puts the Russian sturgeon in a special position with reference to migratory teleostean fish, specifically salmonids, in which the specific weight of the protein of slow and fast hemoglobins undergoes changes upon change of the habitat.     

Intraspecific variability in fractional composition of the serum proteins of the sturgeon Acipenser stellatus]

Comparative studies on fractional composition of the blood serum proteins in two sympatric populations of the sturgeon A. stellatus (South-Caspian and North-Caspian) have been made by means of polyacrylamide gel disc-electrophoresis. Serum proteins are fractionated into 13-18 electrophoretic components, the heterogeneity of proteins being somewhat higher in the North-Caspian population than in the South-Caspian one. Most pronounced differences were found in the relative content of albumins and beta-globulins. Special interest is attracted to different heterogeneity of albumins and beta-globulins (transferrins) in the two populations of the Caspian sturgeon.     

Seasonal migrations and reproductive patterns in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario

This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol. In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development. This revised version was published online in August 2006 with corrections to the Cover Date.     

New strategies for brood stock management of sturgeon in the Sea of Azov basin in response to changes in patterns of spawning migration

The sturgeon stock in the Sea of Azov is presently maintained by artificial reproduction allowing for the harvest of sturgeons in this basin. Shortened spawning migrations in regulated rivers and long-term artificial selection of the ripest fish at the hatcheries have resulted in high functional maturity of sturgeon spawners in the sea near the river mouth. The traditional technology of artificial sturgeon reproduction is non-effective under modern ecological conditions. The use of ecological and hormonal methods to control seasonal propagation of stellate sturgeon, A.stellatus , Russian sturgeon, A.gueldenstaedti , beluga, Huso huso , and sterlet, A.ruthenus , make it possible to stagger the sexual cycle of breeders from the various biological groups for early (5 months) or later (6 months) spawning. Use of these methods preserves the natural heterogeneity of sturgeon populations maintained through stocking, and also allows for a considerable increase in the quantity of fry reared at the same production base.
The use of the synthetic analogue of mammalian gonadotropin-releasing hormone (Gn-RHa) is better for inducing maturity of the ripest brood fishes, especially for stellate sturgeon, in comparison with the traditional pituitary injections. The schedule of injections was determined for the various species and seasons of spawning.
Short-term rearing of larvae in ponds (no more than 15 days) and subsequent adaptation to sea water in brackish lagoons (1–5 %o) allows for repeated use of nursery ponds in sturgeon hatcheries and a considerable increase in the quantity and survival of sturgeon juveniles in the sea.
The restoration of the sturgeon population structure in the Sea of Azov is not possible without developing a genetic collection of the fish under a controlled culture regime.     

Ontogenetic behavior of Siberian sturgeon, Acipenser baerii: A synthesis between laboratory tests and field data

We have reviewed field data and studies on the behavior and development of Siberian sturgeon at early-life intervals and related them to different ecologically relevant environmental factors that may play a role in the distribution, recruitment, and survival of young fish. Four behavioral phases (swimming-up, rheotactism, shoaling, and foraging) are observed from hatching to the juvenile phase. Each behavior is associated with an early-life interval and might allow fish to occupy different river habitats, directly influencing their distribution, survival, and recruitment. River current intensity, substrate typology, food resources, and predation pressure seem to be the most important factors affecting the distribution of Siberian sturgeon free embryos and larvae, while juveniles and adult fish disperse and migrate according to food abundance and reproduction. Mechanisms involved in regulating downstream migration during Siberian sturgeon early life stages are different than those observed in anadromous sturgeon species. In all large Siberian rivers, with the exception of the Lake Baikal, the Siberian sturgeon is represented by population continuums, and in many cases the foraging range also includes the spawning areas. Ontogenetic changes in Siberian sturgeon behavior could be interpreted as a species-specific mechanism to maintain the population continuums described in this species without significant mixture of local populations within the river.     

Lysozyme Content in Organs and Blood Serum in Various Species in the Volga River

The results of study of lysozyme content in kidney, liver, spleen, and blood serum of 12 fish species in the Volga River, which belong to six different orders, are presented. It has been established that the lysozyme level in the organs and blood serum is different in representatives of different taxons. The highest enzyme content was observed in sterlet (order Acipenseriformes), while the lowest content, in burbot (order Gadiformes). The enzyme content and its distribution in visceral organs depended on fish phylogeny, but not on the type of feeding (vegetarian or predatory) and the place of the constant habitation (fresh river or salted sea water). There were seasonal and yearly variations of the lysozyme concentration in fish organs and tissues. The many-year studies have established the regularity in enzyme distribution in sturgeon fish: kidney > spleen > liver > blood serum, this regularity being independent of the sturgeon species and constant during intra- and inter-year variations.     

Implications of early life stages in the natural history of the Gulf of Mexico sturgeon,Acipenser oxyrinchus de sotoi

Synopsis Gulf of Mexico sturgeon were collected during their natural spring spawning migrations from the Gulf of Mexico into the Suwannee River in Florida. Peak numbers were observed during March and April. During the summer periods the fish remained in the river over very localized bottom areas. In late fall, the fish migrated from the river into the Gulf of Mexico. Laboratory experiments revealed that maximum survival of eggs, embryos and larvae of Gulf of Mexico sturgeon occurred between 15 and 20° C. Although Gulf of Mexico sturgeon appear to have a high tolerance to warm water temperatures, their embryos and larvae exhibit high mortalities at temperatures of 25° C. Based on observations of Gulf of Mexico sturgeon migratory patterns and laboratory experiments we suggest that the timing and unusual migratory behavior of Gulf of Mexico sturgeon are associated with temporal water temperature changes in the river and the Gulf of Mexico. The requirements of a thermal refuge are discussed.     

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.     

Changes in the physiological state of hiemal form of the Russian sturgeon Acipenser gueldenstaedtii in the Volga after holding It and hormonal impacts

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.     

Biological characteristics of European Atlantic sturgeon, Acipenser sturio, as the basis for a restoration program in France

The European Atlantic Sturgeon, Acipenser sturio, has received increased attention in France because of population declines due to overfishing and deterioration of spawning grounds. Conservation of this species requires many actions, including publicizing the necessity to protect this fish and its habitats, investigations on catches and probable spawning grounds, and on artificial reproduction, which is still in an experimental stage. During its sea life, European Atlantic sturgeon occur from the Bay of Biscay to the Bristol Channel and North Sea. Presently, the number of young fish in the Gironde Estuary during summertime is low and the population has a unimodal age structure. At the time this paper was written, the last recorded reproduction of sturgeon in the Gironde system occurred in 1988 (new evidence of reproduction was discovered in 1995). Growth of young fish from the 1988 cohort was faster than that previously determined for others cohorts. Over our study period (1980–1994), the availability of wild broodfish declined. Successful artificial reproduction of wild-caught females requires an optimal physiological state; any delay decreases their reproductive potential. Acclimatization of wild-caught juveniles to fresh water was most successful when fish were transported and held upon arrival in low salinity water. For such wild-caught juveniles, the first food intake usually occurs several months after capture, but remains irregular. These findings will be used to improve ongoing efforts to restore A. sturio.     

Steroid hormones in the regulation of migration in fishes (study of the Russian sturgeon)

Serum steroids profiles were determined at different stages of the migratory cycle of Russian sturgeon. In the sea period, before gonads maturation cortisol and sex steroids levels were comparatively low. Elevation of cortisol and testosterone concentrations occurred at the stage of preparation to migration. Significant increase of cortisol and testosterone levels happened at the beginning of the river period of anadromous migration in spring both in the spring forms near to maturity in this period and in the winter forms which were far from maturity. By exception of the river period of anadromous migration of the winter form and sexual cycle completion in the fish farm in the mouth of river (10-11 months), serum cortisol and testosterone concentrations dropped sharply. The data obtained as well as the data on other diadromous fishes indicate a possible role of steroids, especially cortisol and testosterone, in metabolism and migration regulation in sturgeons.     

Diet composition of larval and young-of-year shovelnose sturgeon in the Upper Missouri River

Obtaining food following the transition from endogenous to exogenous feeding and during the first year of life is a critical event that strongly influences growth and survival of young‐of‐year fishes. For shovelnose sturgeon Scaphirhynchus platorynchus, limited information is available on food habits during the first year of life. The objective of this study was to quantify diet components of shovelnose sturgeon during the transition from endogenous to exogenous feeding and during the young‐of‐year life stage in the North Dakota and Montana portions of the Missouri River. Young‐of‐year shovelnose sturgeon were sampled between early August and early September 2003. Shovelnose sturgeon initiated exogenous feeding by 16 mm, and individuals 16–140 mm fed exclusively on two macroinvertebrate orders (Diptera and Ephemeroptera). Young‐of‐year shovelnose sturgeon exhibited an apparently high feeding success as 99 of 100 individuals contained food in the gut. The number of organisms in the gut increased exponentially with fish length for larval Diptera (r² = 0.73, P < 0.0001) and linearly (r² = 0.12, P = 0.0006) for larval Ephemeroptera, but the number of Diptera pupae in the gut was not significantly related (P = 0.55) to length of young‐of‐year shovelnose sturgeon. The length of ingested prey was linearly related to fish length for Diptera larvae (r² = 0.20, P = 0.002), whereas the relationship between lengths of ingested Ephemeroptera larvae and lengths of young‐of‐year shovelnose sturgeon was best described by a power function (r² = 0.50, P < 0.0001). These results provide the first quantification of feeding dynamics for young‐of‐year shovelnose sturgeon in a natural river environment.     

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.     

Assessment of the seasonal usage of the lower Pascagoula River estuary by Gulf sturgeon (Acipenser oxyrinchus desotoi)

The Pascagoula watershed likely offers the greatest possibility for the survival of the Gulf sturgeon, Acipenser oxyrinchus desotoi, within Mississippi. Thus, understanding and preserving the connectivity between distant habitats in this region plays a major role in protecting and managing such anadromous fish populations. The focus of this project was to determine the within‐river routes Gulf sturgeon take through the lower Pascagoula River downstream of the point where it splits (river kilometer 23) into two distinct distributaries. Sixty days were sampled throughout a two‐year period with a total effort of 81 947 net‐meter‐hours and eight Gulf sturgeon were captured, ranging from 74 to 189 cm FL and weighing from 3.6 to 52.6 kg. Using an array of automated telemetry receivers, acoustically tagged Gulf sturgeon movements were monitored within the lower river and associated estuary. Estimated residence times (days) suggest Gulf sturgeon appear to prefer the eastern distributary upriver from Bayou Chemise as the primary travel corridor between freshwater habitats and marine feeding grounds. The western distributary mouth was more highly used by Gulf sturgeon during both seasonal migrations between upriver and offshore habitats. Thus, the western distributary appears to represent the main entrance point utilized by Gulf sturgeon to the Pascagoula River watershed and should be protected as the eastern distributary mouth has been altered from a natural marsh edge to one of hardened surfaces.     

Alteration of immunological properties of bovine serum albumin by covalent attachment of polyethylene glycol.

Methoxypolyethylene glycols of 1900 and 5000 daltons have been attached covalently to bovine serum albumin using cyanuric chloride as the coupling agent. When sufficient polymer is attached, the modified bovine serum albumin appears to lose its immunogenicity in the rabbit and, on intramuscular or intravenous injection, elicits antibodies neither to itself nor to native bovine serum albumin. It does not react with antibodies raised against native bovine serum albumin. Bovine serum albumin to which methoxypolyethylene glycol has been attached exhibits a blood circulating life in the rabbit rather similar to native bovine serum albumin, except that it is not removed from circulation by the eventual development of antibodies. Modified bovine serum albumins which had been iodinated with 125I, or prepared with [14C]cyanuric chloride, were injected intravenously in rabbits. Both labels appeared almost quantitatively in the urine after 30 days. The modified bovine serum albumins showed substantial changes in properties, such as solubility, electrophoretic mobility in acrylamide gel, ion exchange chromatography, and sedimentation, as compared with the unmodified protein.     

Changes of Somatotropin Concentration in Blood Serum of Juvenile Russian Sturgeon <Emphasis Type="Italic">Acipenser gueldenstaedtii</Emphasis> (Acipenseriformes) During Adaptation to Hyperosmotic Medium

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.     

Atlantic and shortnose sturgeons of the Hudson River: common and divergent life history attributes

The Hudson River estuary supports substantial number of Atlantic sturgeon, Acipenser oxyrinchus, and shortnose sturgeon, Acipenser brevirostrum. Both species have complex life cycles that have been studied sporadically in the past 50 years. The life cycle of the shortnose sturgeon may be divided into four life intervals: non-spawning adults, spawning adults, eggs and larvae, and juveniles. The life cycle of the Atlantic sturgeon is reviewed in six intervals: non-spawning adults, female spawners, male spawners, eggs and larvae, early juveniles, and late juveniles. Both species are long-lived, mature at advanced age, have rapid and similar growth during the first few years of life, feed on generally similar taxa, use deep channel habitats for all life intervals, and have complex migratory patterns with distinct, seasonal, concentration areas. Atlantic and shortnose sturgeons differ, however, in ages and sizes at maturity, maximum size, timing and location of spawning, migratory behaviors, and management. Use of marine habitats and long-distance coastal migrations are restricted to Atlantic sturgeon, but some evidence indicates that large Atlantic sturgeon juveniles reside in riverine habitats along the Atlantic coast during warm months. Movements and habitat use by both sturgeons in the Hudson River estuary contrasts with the spatial segregation of the species reported in other river systems. Juvenile shortnose sturgeon and early juvenile Atlantic sturgeon have almost the same distributions in the Hudson River estuary during all seasons. During this period of co-occurrence, both species are very similar in size, grow at about the same rate, feed on similar foods, and share deep, channel habitats. Adult shortnose sturgeon distribution overlaps with the distribution of juvenile Atlantic sturgeon, and the latter commence river emigration at a size comparable to co-occurring adult shortnose sturgeon. Life history information on the Hudson River sturgeons substantiates the need to carefully conserve these species because of vulnerability to exploitation and habitat disruption.     

Divergence of the two albumins of X. laevis. Evidence for the glycosylation of the major 74K albumin

The mRNAs coding for the 68,000 and 74,000 dalton serum albumins of Xenopus laevis were purified by hybridisation to their corresponding cloned cDNA and translated using the reticulocyte lysate. The primary translational product of the 68,000 dalton albumin has a molecular weight of 70,000 daltons suggesting that it is synthesised with a signal peptide which is cleaved during secretion. In contrast, the primary translational product of the 74,000 dalton albumin has a molecular weight of 72,000 daltons suggesting that it must be posttranslationally modified to account for the increased molecular weight of the mature protein. X. laevis oocytes injected with albumin mRNA secrete proteins of the same molecular weights as the mature albumins. When these translational products were chromatographed on concanavalin A Sepharose, the 74,000 dalton albumin was bound suggesting that it is glycosylated. Comparison of X. laevis and X. tropicalis albumins suggests that the 68,000 dalton albumin is similar to the primitive Xenopus albumin and that since the genome duplication which occurred in X. laevis, differences have arisen in both the length and processing of the primary translational product to account for the current difference in the molecular weights of the two X. laevis albumins.     

Divergence of the Two Albumins of X. laevis

The mRNAs coding for the 68,000 and 74,000 dalton serum albumins of Xenopus laevis were purified by hybridisation to their corresponding cloned cDNA and translated using the reticulocyte lysate. The primary translational product of the 68,000 dalton albumin has a molecular weight of 70,000 daltons suggesting that it is synthesised with a signal peptide which is cleaved during secretion. In contrast, the primary translational product of the 74,000 dalton albumin has a molecular weight of 72,000 daltons suggesting that it must be posttranslationally modified to account for the increased molecular weight of the mature protein. X. laevis oocytes injected with albumin mRNA secrete proteins of the same molecular weights as the mature albumins. When these translational products were chromatographed on concanavalin A Sepharose, the 74,000 dalton albumin was bound suggesting that it is glycosylated. Comparison of X. laevis and X. tropicalis albumins suggests that the 68,000 dalton albumin is similar to the primitive Xenopus albumin and that since the genome duplication which occurred in X. laevis , differences have arisen in both the length and processing of the primary translational product to account for the current difference in the molecular weights of the two X. laevis albumins.