A comparative study of feeding methods: Effect on the growth,behaviour and biochemical performance of juvenile Beluga sturgeon (Huso huso Linnaeus, 1758)

This study compared the influence of feeding methods on growth parameters of young‐of‐year Beluga sturgeon Huso huso in a 6‐week trial. Fish with an average weight 150.3 ± 0.8 g (±SE) were stocked into nine circular concrete tanks (30 fish per tank) in an open circular system with water temperature of 18.9°C. All fish were fed by three different feeding methods: (a) hand‐fed (HF), (b) continuously available (automated feeder; AF), (c) half of daily feed provided by hand, and another half by automated feeder (combined feeding). For the hand‐feeding method, fish were fed at 09:00, 14:00, 19:00, and 24:00. The entire automatic feeding groups were fed with the same amount of feed. The mean final body weight was the highest in fish fed by AF compared to fish fed by HF. Body weight increase, condition factor, specific growth rate, and feed conversion ratio did not differ among the feeding groups. Fish fed by AF revealed higher swimming activity than the HF group. No significant changes were found in hematocrit, glucose and total protein concentrations among treatments. The results showed less dependence of growth and physiology of Beluga sturgeon on feeding method, but automated‐feeding was shown to be suitable for sturgeon rearing because of further low labour costs in rearing systems.     

Effects of dietary prebiotic GroBiotic®‐A on growth performance,plasma thyroid hormones and mucosal immunity of great sturgeon,Huso huso (Linnaeus, 1758)

The present study was conducted to evaluate the effects of Grobiotic^®‐A, a commercial prebiotics, when administered in feed on the growth performance, plasma thyroid hormones and mucosal immunity of great sturgeon (Huso huso). The commercial prebiotic mixture was supplemented in the diets at four different levels (i.e. 0.0% as control, 0.5%, 1% and 2%, in three replicates, 20 fish per replicate) and fed to the fish for an 8‐week period wherein 240 fish were cultured in 1,800‐L fiberglass tanks that formed part of a flow‐through system. Water temperature was maintained at 20.4 ± 1.5°C. Significant changes in growth performance parameters were observed, but only in those groups fed with 1% and 2% prebiotics. Specifically, marked improvements relative to the control group were observed in percentage weight gain, body weight gain, feed conversion ratio and specific growth rate in prebiotic‐fed fish. The levels of plasma thyroid hormones, specifically thyroxine and thyroid stimulating hormones were significantly elevated in the group receiving 2% prebiotics. Activities of lysozyme and alkaline phosphatase in skin mucus were significantly enhanced in prebiotics‐fed groups, particularly at an inclusion level of 1% and higher (2% group compared to the control). Inhibitory activity of the skin mucus against pathogens, particularly Streptococcus iniae and Yersinia ruckeri, was significantly improved following prebiotic feeding. Taken together, dietary inclusion of GroBiotic^®‐A promoted growth, modulated thyroid hormones, and enhanced mucosal immunity of H. huso. This prebiotic mixture has the potential for use in improving the growth performance and health status of farmed great sturgeon.     

Effect of prebiotic mannan oligosaccharide on hematological and blood serum biochemical parameters of cultured juvenile great sturgeon (Huso huso Linnaeus, 1754)

The nutritional effects of prebiotic mannan oligosaccharide were evaluated using hematological and blood serum biochemical parameters in cultured juvenile great sturgeon (Huso huso). Fish were offered formulated diets containing two levels of prebiotic mannan oligosaccharide (2 and 4 g kg^?1); a basal diet with no prebiotics was used as control. The experiment lasted for 46 days. Blood samples were collected from the caudal veins of 18 apparently healthy fish (average weight 217.77 ± 29.8 g) at the end of the trial. No significant differences were found in the serum enzyme activity levels between treatments (P > 0.05). However, adding mannan oligosaccharide as a supplement to the basal diet resulted in significant differences in lymphocytes and eosinophils between the control and the 2 g kg^?1 treatment (P < 0.05) as well as a significant difference in the creatinine factor in the 2 g kg^?1 mannan oligosaccharide treatment (P < 0.05). The results show that it would be advantageous to add 2 g kg^?1 mannan oligosaccharide to the diets of juvenile great beluga sturgeon (Huso huso).     

Responses to handling and confinement stressors in juvenile great sturgeon Huso huso

The effects of acute stressors on physiological responses of juvenile great sturgeon or beluga Huso huso L. were investigated in two experiments. In the first experiment, fish were handled by placing them in containers at either low density (LD, one fish l^?1) or high density (HD, four fish l^?1) for 60 s. Concentrations of plasma cortisol, glucose and lactate were determined from blood collected at 0, 1, 3, 6 and 12 h after application of the stressor. Plasma cortisol concentrations increased after the disturbance in H. huso from both handling treatments, but changes were not significant. Plasma glucose rose significantly by 22·9 and 31·6% in LD and HD handling treatments, respectively, after 3 h. Significant increases in plasma lactate occurred within 1 h in both treatment groups, but that of the HD group was much higher. In the second experiment, fish were held at two different densities, LD (2 kg m^?2 tank bottom surface area) and HD (7 kg m^?2), for 8 weeks and then subjected to an aerial emersion handling stressor in a net for 60 s; blood samples were taken before handling (resting, 0 h) and at 1, 3, 6 and 9 h after handling. Plasma cortisol increased significantly in fish from the HD treatment from 8·8 ± 0·3 to 19·2 ± 2·4 ng ml^?1 (mean ±s.e. ) by 1 h after stress, but post‐handling changes in the LD group were not significant. Significant increases in both plasma glucose and lactate were observed by 1 h in both treatment groups, with peak levels of plasma glucose evident at 3 h [69·4 ± 2·9 and 60·9 ± 1·7 mg dl^?1 (mean ±s.e .) in LD and HD groups, respectively]. Plasma glucose levels were significantly higher in the LD group than in the HD group at 3 and 6 h. Post‐handling haemoglobin content increased by 1 h and white blood cell numbers were reduced by 3 and 6 h in the HD treatment group compared with resting values, but changes in these blood features in the LD group were not significant. Acute handling did not affect haematocrit in either treatment. The results suggest that H. huso is relatively resistant to handling and confinement, and could tolerate normal hatchery practices associated with aquaculture. Because changes in cortisol concentrations were relatively low compared with those in most teleosts, glucose and lactate concentrations may be more useful as stress indicators in juvenile H. huso. This study also demonstrated that prior exposure to a chronic stressor, specifically high stocking density, could alter the physiological response to subsequent acute handling in H. huso.     

Optimal stocking density for beluga,Huso huso,and ship sturgeon,Acipenser nudiventris during the grow‐out phase

The influence of three different initial stocking densities (SD) in flowthrough systems was evaluated on growth performance and feed utilizaition in beluga, Huso huso, and ship sturgeon, Acipenser nudiventris, juveniles in three different grow‐out phases for 228 days. In each grow‐out phase, fish were randomly distributed in 18 concrete square tanks (2.0 × 1.0 × 1.2 m³; 2 m³ of volume) according to the experimental SD. At the first phase, both fish species were subjected to three SD including 1.5, 3 and 6 kg/m² for 60 days. In the second phase, fish were submitted to three SD including 3, 6 and 9 kg/m², whereas in the third phase, beluga were stocked at 6, 9 and 12 kg/m² and ship sturgeon were stocked at 6, 8 and 10 kg/m² and each phase lasted for 12 weeks. In both species, the growth performance and feed intake (FI) significantly decreased with increasing SD at the end of the first phase (p < 0.05). In the second phase, growth performance and FI in beluga decreased with increasing SD, whereas in ship sturgeon neither growth nor FI were affected by SD. Interestingly, the growth performance and feed utilization in both species were not decreased with increasing SD in the third phase indicating adaptability of these species to high stocking density during grow‐out period. According to the result of this study, the appropriate initial SD for beluga within the range of 100–500, 500–2,000 and 1,500–3,000 g were at 1.5, 6 and 12 kg/m², respectively in an open flow‐throw system. Regarding to ship sturgeon, initial SD at 1.5 and 10 kg/m²recommended for fish within the range of 100–300 and 300–1,200 g, respectively in an open flow‐throw system.     

Formation of populations of Acipenseridae sturgeons in the Volga-Caspian basin

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.     

Organization of the diencephalon ventrothalamic area in the sturgeons

Cytoarchitectonics of ventrothalamic area of the diencephalon of the sturgeons was studied in four species of the sturgeons, the great sturgeon Huso huso L., the Kura sturgeon Acipenser guelden-staedtii persicus n. Kurensis Belyaeff, the Caspian sturgeon, Ac. stellatus Pall., and the barbel sturgeon Ac. nudioventris Lov. using Nissl staining and Bilschowski impregnation techniques in Viktorov’s modification. The ventral thalamus of the sturgeons was found to include seven nuclei: ventromedial, ventrolateral, intermediate and ventral thalamic nuclei, thalamic eminence, and nuclei of ventral and medial optic tracts. The main attention was paid to comparative analysis of this area in the sturgeons and other actinopterygian fish. The structures common to all ray-finned fish or only to the lower teleosts and ganoids as well as characterizing only the sturgeons.     

Effects of long-term cortisol treatments on gonadal development, sex steroids levels and ovarian cortisol content in cultured great sturgeon Huso huso

The objective of this study was to examine the effect of cortisol implantations on gonadal development, sex steroid levels, and ovarian cortisol content in cultured great sturgeon Huso huso. Three groups of 5 fish for each treatment were considered. The experimental groups included: control (capsules containing cocoa butter alone), low cortisol (C(5); 5mg cortisol/kg body mass+cocoa butter) and, high cortisol (C(50); 50mg cortisol/kg body mass+cocoa butter). The capsules containing hormones and cocoa butter were intraperitoneally implanted into 3-year-old female fish at pre-vitellogenic stage (mean initial body mass 6809.7 ± 73 g) every 6 weeks over a 6-month period from January to June. The serum levels of cortisol, glucose, cholesterol and sex steroids (testosterone and 17β-estradiol) were determined at the initial time and three weeks after each implantation. Oocyte histological characteristics (the diameter and area of the oocyte, the diameter and area of the nucleus and the ratio of the nucleus area to the oocyte area) were measured at the end of the experiment and compared to those at the initial time. Ovarian cortisol content was measured at the end of the experiment. The results showed that serum cortisol levels varied in a dose-independent manner, so that the highest cortisol concentrations were observed in C(5)-treated fish throughout the experiment. Serum glucose levels were significantly higher in cortisol-treated groups than those in the control group. The high dose of cortisol elicited a significant constant increase in serum cholesterol concentrations. Fish implanted with the high cortisol dose showed significant declines in serum testosterone and 17β-estradiol concentrations throughout the experiment. No significant differences were found in oocyte histological characteristics among experimental groups. The cortisol implants elicited a dose-dependent increase in ovarian cortisol content. At the end of trial, body-growth indices were the lowest in C(50)-implanted fish, while the low cortisol dose had no effect on growth relative to the controls. These results indicated that chronic stress induced by cortisol implantation in great sturgeon suppressed gonadal steroidogenesis and somatic growth but had no effect on ovarian growth and development.     

Production of recombinant great sturgeon (Huso huso,Linnaeus, 1758) growth hormone (GH) by Pichia pastoris (Guillierm, 1956)

In this research, the encoding cDNA of growth hormone (GH) was cloned from the pituitary gland of great sturgeon Huso huso (three adults: two females and one male, 7–9 years old, 70–90 kg, reared in concrete ponds). In order to obtain the great sturgeon recombinant GH expression in Pichia pastoris, the mature encoding cDNA was first cloned in TA vector PTZ57R and then sequenced. After confirmation of the correct GH sequence, the GH coding sequence was subcloned into pHILS1 expression vector. The yeast Pichia pastoris GS115 strain was transformed with the expression plasmid. Results obtained from this study showed that great sturgeon GH recombinants were expressed upon induction with methanol and exported into the medium. The level of expression was examined using RNA analysis, SDS‐PAGE, and western blot analysis. RNA analysis of the recombinant strains showed a sharp, specific band in 800 bp. The specific band in transformants indicated the presence of GH RNA in the yeast. SDS‐PAGE and western blot analysis showed a specific 21 kDa band for the growth hormone. Culture conditions were optimized for pH = 6 and incubation time (after 24 h induction, peaking at 72 h) for maximal protein production. The results provide useful information for the future production of recombinant growth hormones in other sturgeon species.     

Developmental structure of the vertebral column,fins, scutes and scales in bester sturgeon,a hybrid of beluga Huso huso and sterlet Acipenser ruthenus

In the larval bester, a hybrid sturgeon of beluga Huso huso and sterlet Acipenser ruthenus, development of cartilage around the notochord began 7 days post hatch (dph) (14·0 mm, total length, L_T). The vertebral cartilage develops in the following sequence: basidorsals and basiventrals, neural canals, neural spines and ribs. The development of ribs remained incomplete in the largest specimen (181 dph, 179 mm L_T) that was examined. Endoskeletal development of the fins began 4 dph for the dorsal and anal fins, 6 dph for the pectoral fin and 10 dph for the caudal and pelvic fins. Complete elements of all fins were observed by 91 dph and complete ossification of fin rays was observed by 122 dph in the double‐stained specimens. Observation of the histological sections, however, suggested that ossification occurred soon after the formation of the organic matrix in the fin rays. Dorsal scutes were first visible by 25 dph, followed by the lateral and ventral scutes, which were visible by 37 and 44 dph, respectively. The number of scutes was fixed at 44, 59 and 91 dph and ossification was complete by 59 (dorsal) and 91 dph (lateral and ventral scutes) in the double‐stained specimens. Ossification occurred soon after the formation of the scute organic matrix in the histological sections. Four types of scales were observed in the H. huso×A. ruthenus hybrid. Median predorsal, preanal and small scales on the anterior section of the head were visible by 59 dph. Scales on the caudal fin were visible by 91 dph and a variable assemblage of scales anterior to the anal fin was visible by 122 dph. Both the scutes and scales developed in a process that is similar to that of intramembranous ossification.     

Factors influencing the natural reproduction decline in the beluga (Huso huso,Linnaeus, 1758), Russian sturgeon (Acipenser gueldenstaedtii,Brandt & Ratzeburg, 1833), and stellate sturgeon (A. stellatus,Pallas, 1771) of the Volga–Caspian basin: A review

The review describes the changes in natural reproduction of three important sturgeon species in the Volga–Caspian basin: (a) the beluga (Huso huso Linneaus, 1758), (b) the Russian sturgeon (Acipenser gueldenstaedtii Brandt &Ratzeburg, 1833), and (c) the stellate sturgeon (Acipenser stellatus Pallas, 1771). Since the past 60 years, these species responded to severe influences of natural and anthropogenic factors. On the basis of original and published data, an analysis has been made of (a) the numbers of larvae migrating from spawning sites (according to plankton net survey), (b) fecundity and histological anomalies in gonad development, (c) the numbers of adult sturgeons in the Caspian Sea and of spawners migrating to the Volga River (according to trawl and beach seine survey), and (d) foraging resources for the sturgeons. The results show that their natural reproduction in the Volga–Caspian basin has declined drastically during the past decades under the impact of (a) fluctuations of the Caspian Sea level and flow discharge from the Volga River, (b) blockage of sturgeon migration routes and loss of spawning sites because of dam construction, (c) water pollution in the lower reaches of the Volga River and in the Caspian Sea, and (d) intensive and selective illegal and unreported fishing. The relative significance of these factors has been changing during the study period.     

The RAPD technique failed to identify sex-specific sequences in beluga (Huso huso)

Because the sex of sturgeon cannot be determined externally until the pre‐spawning phase, they are currently sexed by means of minor surgery. Although the survival rate is nearly 100%, this surgery is invasive. One effective solution is to use DNA markers to diagnose the sex. In this study we employed bulked segregant analysis methodology to screen for genetic markers associated with the sex of the beluga (Huso huso). DNA bulks (male and female) were created by combining equal amounts of genomic DNA from 10 fish of both sexes. A total of 310 randomly amplified polymorphic DNA primers was used to screen the bulks, resulting in 4146 bands that were present in both sexes. Our results suggest that either the sex‐specific DNA in sturgeon may be comprised of sequences not complementary to 310 random decamer primers or that sex chromosomes are weakly differentiated in the sturgeon genome.     

Compensatory growth in sub‐yearling Siberian sturgeon,Acipenser baerii Brandt, 1869: Effects of starvation and refeeding on growth,feed utilization and body composition

The capacity of sub‐yearling Siberian sturgeon (Acipenser baerii Brandt, 1869) (19.7 ± 0.8 g) to show compensatory growth was assessed for a 40‐day period for the effects of short‐term starvation and refeeding on growth, feeding performance and body composition. After acclimation, 25 experimental fish were randomly distributed among twelve 500‐L cylindrical fiberglass tanks with a flow‐through system. The fish were subjected to four different feeding regimes: control, which was fed four times daily to apparent satiation; T₁: four periods of 2 days starvation alternating with 8 days re‐feeding; T₂: two periods of 4 days starvation alternating with 16 days refeeding; T₃: an 8 days starvation period followed by 32 days refeeding. At the end of the experiment, the deprived fish attained body weights comparable to those attained by the control fish. There were no differences in growth and feeding performances between the deprived and the control fish. Total protein and lipid contents of the control fish were significantly higher than that of T₁ and T₂ fish at the end of the experiment (P < 0.05). A significant difference in the energy content was observed between T₂ and the control. Siberian sturgeon exhibited complete compensation, indicating a high ability of the deprived fish to grow sufficiently to fully compensate for weight loss during starvation. The results suggested that the feeding schedule involving starvation–refeeding cycles could be a promising feed management option for the culture of this species.     

Diet of farm‐escaped sturgeon in the Yangtze River

The diet of farm‐escaped sturgeon accidentally introduced into the Yangtze River ecosystem was investigated from samples collected over 10 days. The fish had consumed adequate quantities of natural food, with prey type related to fish body size. The fish were categorized according to their primary dietary component: demersal fish were most common prey of kaluga Huso dauricus and H. dauricus × Acipenser schrenckii hybrids of total length 120.3–188.7 cm. Shrimp Macrobrachium nipponensis made up the major portion of the diet of H. dauricus × A. schrenckii and Acipenser baerii × A. schrenckii of total length 91.1–106.8 cm. Gammarid amphipods were consumed by A. baerii × A. schrenckii of total length 35.0–81.2 cm. The body length of prey was proportional to the fork length of the sturgeon, Y = 0.19X‐9.46, R² = 0.997. Escaped sturgeon had travelled at least 898 km downstream from the point of escape in the Yangtze River and were feeding on native macrobenthos and demersal fish.     

Assessment of Extinction Risk and Reasons for Decline in Sturgeon

Sturgeon populations in the Danube River have been affected by a combination of hydropower development, over-harvesting, habitat degradation from agricultural and industrial practices and from urbanization. The effects of these changes have been monitored on six sturgeon species inhabiting the Danube River. Two of them are resident species, while the other four migrate to the river for spawning. Atlantic sturgeon (Acipenser sturio) has completely disappeared from this region. Ship sturgeon (Acipenser nudiventris) is very rare in professional fishing catches. Beluga (Huso huso), Russian sturgeon (Acipenser gueldenstaedtii), stellate sturgeon (Acipenser stellatus) and sterlet (Acipenser ruthenus) are endangered with different levels of extinction risk. Here, we model the time dependence of the beluga and Russian sturgeon catch in the Serbian part of the Danube River. Predicted extinction of Russian sturgeon was estimated to fall around the middle of the century, and for beluga approximately at middle of the millennium. Suggestions for sturgeon conservation measures on a national level and coordination of all relevant institutions in Serbia are also presented.     

Differential expression of foxl2 and cyp19a1a mRNA during gonad developmental stages in great sturgeon Huso huso

This study aimed to determine the sex specificity and expression pattern of foxl2 and cyp19a1a genes in great sturgeon Huso huso gonads during gonadal sex differentiation and development. The results revealed that foxl2 and cyp19a1a mainly expressed in female gonads and during gonad development the foxl2 and cyp19a1a mRNA expression is required for ovarian development.     

Sturgeons in Greece: a review

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

Early sex identification of 18‐month cultured beluga sturgeon (Huso huso) using ultrasonography,small surgery and plasma steroid hormones

Since sturgeons do not show clear sexual dimorphism particularly when are small in size, attempts were made to determine the best methods to identify early sex in farmed beluga sturgeon (Huso huso). The present study describes the ultrasonography, small surgery and plasma steroid hormone methods to determine gender at 18‐month fish, which no research has been conducted yet into the fish at such small ages. Twenty one cultured beluga sturgeon's gonad were imaged using an ultrasonograph unit with a 9–13 MHz linear transducer. Overall accuracy of sex determination using ultrasonography was 80.95%. Plasma testosterone (T) levels were significantly higher in males than in females whereas 17α,20βOH‐P levels were significantly higher in females than in males. Testosterone (T) and 17α,20βOH‐P were not correlated with morphometric parameters (TL, SL, W, CF) in 18‐month beluga sturgeon. Results of this study indicated that sex could be identified by each of ultrasonography, small surgery and analysis of blood plasma in such a small size (18‐month). Although direct observation was more efficient than the other methods, ultrasonography was the simplest and cost‐effective tool in sturgeon's sex determination compared to other methods, and the least invasive.     

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.