Digestive enzyme complement of white sturgeon (Acipenser transmontanus)

Digestive processes of 250-day-old white sturgeon were analyzed for enzyme concentrations, protein content and pH. Digestion is initiated in the gastric region by secretion of acid and pepsin; however, diversity of digestive enzymes is highest in the post-gastric alimentary canal with the greatest proteolytic activity in the spiral valve. Domination of the enzyme complement by proteases is consistent with this species carnivorous feeding habits.     

Transmission of white sturgeon iridovirus in Kootenai River white sturgeon Acipenser transmontanus

It is thought that white sturgeon iridovirus (WSIV) is transmitted vertically from adult white sturgeon Acipenser transmontanus to progeny, and that wild adults are carriers of this virus. Based on this assumption, egg disinfection trials were initiated using wild Kootenai River white sturgeon. Over 2 consecutive years, post-fertilized eggs were disinfected with iodine at concentrations ranging from 0 to 400 ppm. Eggs were incubated and progeny were reared on either de-chlorinated municipal or Kootenai River water. Juvenile sturgeon (mean weight 3.0 g) from these treatment groups were then subjected to a density stress (15 or 20 g(-1)) to manifest WSIV disease in individuals harboring the virus. In Year 1, mortality in all groups ranged from 6 to 37% and the use of municipal water was shown to significantly improve survival. However, WSIV infection was not detected in fish from any of the treatment groups or controls, and therefore did not contribute to the observed mortality. In Year 2, all treatment and control groups reared on Kootenai River water tested positive for WSIV infection and exhibited mortality ranging from 59 to 94%, but fish from groups reared on municipal water did not test positive for WSIV infection. This shows that that vertical transmission did not occur in this study. Horizontal transmission played a significant role in WSIV infection, but the lack of infection in Year 1 suggests a cyclic occurrence of the virus in the Kootenai River system. Although survival tended to be better in iodine-treated groups, the effects of iodine treatment in relation to WSIV transmission remain unknown. An important finding is that not all wild white sturgeon broodstock yield WSIV-positive progeny.     

Recovery plan for Kootenai River white sturgeon (Acipenser transmontanus)

The white sturgeon ( Acipenser transmontanus ) of the Kootenai River was listed as endangered on September 6, 1994 by the United States Fish and Wildlife Service. This transboundary population, residing in Kootenay Lake and Kootenay River in Canada, and the Kootenai River in the US, has been in general decline since the mid-1960's. There has been very little recruitment to this population in the last 20 years.
This population became isolated from other white sturgeon populations of the Columbia River basin during the last ice age of approximately 10,000 years ago. The population adapted to the pre-development conditions of the Kootenai system, with a high spring freshet and extensive side channel and low-lying delta marshlands. Modification of the Kootenai River by human activities, such as industrial developments, floodplain dyking, and dam construction has changed the hydrograph of the Kootenai River, altering sturgeon spawning, incubation and rearing habitats and reducing overall biological productivity.
A Kootenai River white sturgeon draft recovery plan was prepared by the US Fish and Wildlife Service in cooperation with other agencies in the US and Canada. The plan was peer reviewed and there was a parallel public consultation process, where public commentary was invited from both sides of the international border. The short-term recovery objectives of the recovery plan are to prevent extinction and re-establish successful natural recruitment. The identified long-term objectives are the re-establishment of a self sustaining population and the restoration of productive habitat, in order to downlist to threatened status and subsequently delist this population when recovery is well established. Specific actions needed for recovery include spring flow augmentation during the reproduction period; a conservation aquaculture program to prevent near-term extinction; habitat restoration, and research and monitoring programs to evaluate recovery progress.     

Characterization of vitellogenin from white sturgeon,Acipenser transmontanus

Sturgeon are an ancient family (Acipenseridae) of fishes that lie close to the divergence of fish that eventually evolved into terrestrial animals and those that evolved into modern teleost species. Therefore, white sturgeon vitellogenin sequences fill a gap in the current understanding of the functional domains of this protein family. Vitellogenin cDNA was sequenced and used to investigate gene expression in white sturgeon, Acipenser transmontanus. Estrogen-induced vitellogenin mRNA was detected in the livers of both males and females and was also detected in undifferentiated gonads of estrogen-treated fish. Low levels of vitellogenin mRNA were also detected in the testis of both control and estrogen-treated males. The cDNA encoded a 186-kDa protein that was missing only six to seven of the amino-terminal amino acids. Comparisons to silver lamprey, Xenopus, and chicken vitellogenin sequences indicate that the overall structure of the yolk protein domains were highly conserved. There was considerable homology in three regions of the lipovitellin I domain. These conserved sequences are likely to be involved in vitellogenin receptor binding. The phosvitin domain of white sturgeon vitellogenin contained fewer and shorter serine repeats as predicted from yolk protein phosphate content of fish compared to Xenopus and chicken. However, the vitellogenin of white sturgeon had a lower serine content as compared with silver lamprey, indicating that an increased serine content is not strictly a function of evolutionary age. Correspondence to: C. A. Bidwell     

Inheritance of microsatellite loci in the white sturgeon (Acipenser transmontanus).

Nine tetramer motif (GATA)n microsatellite systems were developed for use in the white sturgeon, Acipenser transmontanus. We report inheritance patterns for these nine systems, which range from one possible disomic system to tetrasomy and octosomy, with some systems containing null alleles. Because of the complex modes of inheritance underlying these systems and the highly duplicated nature of the genome, we propose each allele be scored as its own dominant marker, similar to AFLPs or RAPDs. The utility of this method is validated by the observation that individual alleles within a microsatellite system generally fit the expectation for independent transmission and fit the expected transmission frequency for single copy nuclear markers.     

Osmoregulation in juvenile and adult white sturgeon,Acipenser transmontanus

Synopsis Blood samples from cannulated young adult (2.5–15 kg) white sturgeon, acclimated to San Francisco Bay water (24 ppt) had plasma values of 248.8 ± 13.5 mOsm kg⁻¹ H₂O, [Na⁺] = 125 ± 8.0 mEq 1⁻¹, [K⁺] = 2.6 ± 0.8 mEq 1⁻¹ and [CL⁻] = 122 ± 3.0 mEq 1⁻¹. Freshwater acclimated sturgeon had an osmolality of 236 ± 7, [Na⁺] = 131.6 + 4.4, [K⁺] = 2.5 ± 0.7 and [CL⁻] = 110.6 ± 3.6. Freshwater acclimated fish gradually exposed to sea water (increase of 5 ppt h⁻¹) had higher plasma osmolalities than did the bay water acclimated fish. These young adult sturgeon are able to tolerate transfer from fresh water to sea water as well as gradual transfer from sea water to fresh water. Plasma electrolytes in transferred fish are regulated, but tend to differ from long term acclimated fish at the same salinities. There is a gradual increase in the upper salinity tolerance (abrupt transfer) of juvenile white sturgeon with weight: 5–10 ppt for 0.4–0.9 g fish, 10–15 ppt for 0.7–1.8 g fish, and 15 ppt for 4.9–50.0 g fish. The ability of juveniles to regulate plasma osmolality is limited. The young adult fish are able to tolerate higher salinities (35 ppt) than juvenile sturgeon but probably are also characterized by low activity of the necessary ion exchange mechanisms in the gills which permit rapid adjustment of blood electrolytes with graduate change in external salinity.     

An investigation of the substrate preference of white sturgeon (Acipenser transmontanus) eleutheroembryos

Fifty white sturgeon (Acipenser transmontanus) eleutheroembryos (average size 0.17 g) were placed onto each of four quadrants (0.45 m² quadrant⁻¹; 200 fish tank⁻¹) of different sized substrates in four circular tanks (approximately 562 L). Each of three quadrants had a different size substrate and the fourth quadrant was left bare. We used one replicate of smaller size substrates (0.5–11.9 mm) and one replicate of larger size substrates (21.7–88 mm). It was found that the white sturgeon eleutheroembryos preferred substrate with an average size (longest diameter) of 12 mm (11.9) in the smaller substrate range and 22 mm (21.7) in the larger substrate range. These data improve our knowledge of white sturgeon early life history, and if confirmed in the wild can be used to protect areas that are crucial for white sturgeon recruitment and survival.     

Pericardial and pericardioperitoneal canal relationships to cardiac function in the white sturgeon (Acipenser transmontanus)

Sturgeons are primitive bony fishes and their hearts have structural features found in other primitive fishes. Sturgeons have a pericardioperitoneal canal (PPC), a one-way conduit into the peritoneum. A PPC also occurs in elasmobranchs (sharks and rays) and studies with that group demonstrate that pericardial pressure and pericardial fluid loss via the PPC affect stroke volume. A study of white sturgeon (Acipenser transmontanus) heart function was conducted to test for a comparable PPC and pericardial effects. White sturgeon-elasmobranch heart-function similarities include biphasic ventricular filling, a comparable operational pericardial pressure (-0.03 kPa), and a strongly negative pressure (-0.2 to -0.6 kPa) with complete pericardial fluid withdrawal. Differences include the white sturgeon's relatively smaller atrium and ventricle but a larger conus arteriosus. Although white sturgeon heart size is also smaller, its pericardial volume is disproportionately less (2.4 to 2.7 vs. 3.5 to 5.4 ml kg(-1) in elasmobranchs), meaning it has less scope for increasing stroke volume upon PPC fluid release. These differences may reflect the phylogenetic progression from the less complex operation of the elasmobranch heart, which lacks sympathetic innervation and has a mechanically mediated (PPC) stroke volume, to the condition in the more derived bony fishes which have sympathetic and parasympathetic regulation of both stroke volume and heart rate.     

Ultrastructural features of the gut in the white sturgeon, Acipenser transmontanus

Electron-microscopic examinations of the sturgeon gut were performed. Oesophageal goblet cells were abundant in the stratified epithelium. The ultrastructural features of the secretory granules of the oesophageal and intestinal goblet cells were quite similar to those of other vertebrates. Lobules of multilocular adipose tissue were observed in the deep tunica propriasubmucosa of the oesophagus, in close association with vasculature and large fibre bundles of myelinated and unmyelinated axons. Similarly composed nerve fibre bundles were observed in the cardiac stomach, too. The presence of myelinated axons is an unusual feature in the vertebrate enteric nervous system. Cardiac and fundic zones of the stomach showed an epithelium with columnar ciliated and non-ciliated cells, the latter equipped with fuzzy microvilli. Cells lining the tubular gastric proper glands were markedly granulated. Intestinal superficial epithelium was columnar and contained ciliated, as well as non-ciliated and goblet cells. In the tunica propria all over the intestine, the presence and ultrastructure of granulated cells was in addition described. Intraepithelial granulated leukocytes were seen throughout the alimentary canal. Various types of endocrine cells were seen both in the stomach and in the intestine, the size of their granules was measured and their ultrastructure described and compared to that of mammalian cell types.     

Intraspecific DNA sequence variation of the mitochondrial control region of white sturgeon (Acipenser transmontanus)

Intraspecific sequence variation in the D-loop region of mtDNA in white sturgeon (Acipenser transmontanus), a relict North American fish species, was examined in 27 individuals from populations of the Columbia and Fraser rivers. Thirty-three varied nucleotide positions were present in a 462-nucleotide D-loop sequence, amplified using the polymerase chain reaction. Bootstrapped neighbor-joining and maximum- parsimony trees of sequences from 19 haplotypes suggest that the two populations have recently diverged. This is consistent with the hypothesis that the Columbia River, a Pleistocene refugium habitat, was the source of founders for the Fraser River after the last glacial recession. On the basis of a divergence time of 10-12 thousand years ago, the estimated substitution rate of the white sturgeon D-loop region is 1.1-1.3 x 10(-7) nucleotides/site/year, which is comparable to rates for hypervariable sequences in the human D-loop region. Furthermore, the ratio of mean percent nucleotide differences in the D- loop (2.27%) to that in whole mtDNA (0.54%, as estimated from restriction-enzyme data) is 4.3, which is similar to the fourfold-to- fivefold-higher substitution rate estimated for the human D-loop. The high nucleotide substitution rate of the hypervariable region indicates that the vertebrate D-loop has potential as a genetic marker in molecular population studies.      

Observations on the reproductive cycle of cultures white sturgeon, Acipenser transmontanus

Males and females of cultured white sturgeon, Acipenser transmontanus, mature at an average age of 4 and 8 years, respectively. However, the onset of ovarian vitellogenesis and puberty are highly asynchronous in the female stock. Gonadal cycles are annual in males and biennial in females, and gametogenesis is influenced by season. Neuroendocrine regulation of reproduction appears to involve a dual gonadotropin system controlling gonadal development and spawning. Labile puberty and sex-specific duration of the gonadal cycle are distinct characteristics of cultured and wild sturgeon. Photoperiod and temperature play a significant role in environmental regulation of the reproductive cycle, but further studies are necessary to elucidate the roles of endogenous and environmental factors in sturgeon reproduction which is critically important for both aquaculture and conservation of endangered wild stocks.     

Key transitions in morphological development improve age estimates in white sturgeon Acipenser transmontanus

We reared white sturgeon Acipenser transmontanus under laboratory conditions and found that a random-forest model containing scute counts and total length predicted age significantly better than total length alone. Scute counts are rapid, inexpensive and non-lethal meristics to gather in the field. This technique could improve age estimates of imperilled sturgeon populations.     

Comparative stable isotope analyses of green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) in the San Francisco estuary

Green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) are closely related, sympatric species that inhabit the San Francisco estuary. Green sturgeon have a more marine life history but both species spawn in the Sacramento River and reside for some duration in San Francisco Bay. These sturgeons are of conservation concern, yet little is known about their dietary competition when they overlap in space and time. To examine evidence of dietary differentiation, we collected whole blood and blood plasma from 26 green sturgeon and 35 white sturgeon in San Francisco Bay. Using carbon and nitrogen stable isotope analyses, we compared their relative trophic levels and foraging locations along the freshwater to marine gradient. Sampling blood plasma and whole blood allowed comparison of dietary integration over shorter and longer time scales, respectively. Plasma and whole blood δ¹³C values confirmed green sturgeon had more marine dietary sources than white sturgeon. Plasma δ¹⁵N values revealed white sturgeon fed at lower trophic levels than green sturgeon recently, however, whole blood δ¹⁵N values demonstrated the two species fed at the same trophic level over longer time scales. Larger individuals of both species had higher δ¹³C values than smaller individuals, reflecting more marine food sources in adulthood. Length did not affect δ¹⁵N values of either species. Isotope analyses supported the more marine life history of green than white sturgeon and potentially highlight a temporary trophic differentiation of diet between species during and preceding the overlapping life stage in San Francisco Bay.     

Oocyte maturation in white sturgeon,Acipenser transmontanus: some mechanisms and applications

Synopsis The ovaries of four pre-spawning white sturgeon females were sampled and their oocytes incubated in the presence of eight gonadotropin preparations, 21 steroids, a prostaglandin and a catacholamine. Among the gonadotropin preparations, acetone dried pituitary gland powder from white sturgeon, common carp and chum salmon (in decreasing order of potency) were capable of inducing oocyte maturation (germinal vesicle breakdown — GVBD), while human chorionic gonadotropin, pregnant mare's serum gonadotropin, equine luteinizing hormone, bullfrog gonadotropin, and a stellate sturgeon pituitary chromatographic fraction capable of inducing testosterone production in white sturgeon testicular tissue failed to elicit any oocyte maturation response. The progesterone derivatives were the most potent steroid inducers of GVBD, followed closely by several corticosteroids. In vitro incubation of white sturgeon oocytes, in the presence of a suitable steroid (progesterone), can be used as a diagnostic tool in screening out unresponsive females for induced spawning work. The two remaining compounds, prostaglandin F_2a and epinephrine, failed to cause ovulation in progesterone-matured white sturgeon oocytes.     

Influence of temperature on yolk utilization by the white sturgeon, Acipenser transmontanus

The utilization of yolk nutrients by the white sturgeon was investigated at incubation temperatures of 11, 14, 17, and 20° C. The rates of development and dry matter loss are temperature dependent, with an upper critical temperature between 17 and 20° C above which survival is reduced (the temperature range investigated was not sufficient to allow determination of a lower critical temperature). The patterns of yolk utilization are similar to those of other fish. Protein depletion occurs at relatively constant rates throughout yolk nutrition, with the highest rate observed at 20° C. More than 95% of the original lipid levels were still present at hatch, except at 20° C (88%). After hatch, lipid content rapidly decreased at all temperatures, with fish incubated at 11° C possessing higher lipid levels at yolk depletion. The question of why the temperature tolerances of early life stages are more limited than those of older fish is discussed.     

Composition of muscle tissue of farmed white sturgeon (Acipenser transmontanus) with particular reference to lipidic content

The study considers the lipid content of farm-raised sturgeon, Acipenser transmontanus , from northern Italy (commercial size: 24 sturgeon each weighing 5kg; 24 sturgeon each weighing 10 kg). Considered parameters included total lipids, proteins and subsample analysis as saturated and unsaturated fatty acids. The results revealed no variation with seasonal change. Lipid percentages showed the presence of highly unsaturated fatty acids. Both sturgeon sizes investigated showed uniformity in the composition of individual fatty acids of muscle tissue, a factor that can be attributed to the constancy of the culture conditions (feed and water temperature). The product is of reduced lipidic content and high nutritional and market value; as a low fat product sturgeon can be used fresh, and as a semi-fat product may be smoked or canned.     

Gamete interaction in the white sturgeon Acipenser transmontanus: a morphological and physiological review

Synopsis Sturgeon gametes differ from those of most fish in that the sperm possess acrosomes that undergo exocytosis and filament formation while the eggs possess numerous micropyles. Acipenser transmontanus eggs are encased by multilayered envelopes that consist of outer adhesive jelly coats and three structured layers interior to the jelly. The glycoprotein jelly layer only becomes adhesive upon exposure to freshwater. The layer interior to the jelly, layer 3, is the other carbohydrate-containing component of the egg envelope. This layer consists of a water-insoluble glycoprotein that, upon freshwater exposure, is hydrolyzed by a trypsinlike protease to yield a water-soluble, lower molecular weight carbohydrate-containing component. This component can be identified in the surrounding medium when unfertilized eggs are incubated in freshwater. This egg water component elicits acrosome reactions only in homologous sperm. The A. transmontanus sperm acrosome reaction is a Ca⁺⁺ and/or Mg⁺⁺ dependent event that includes the formation of a 10 μ long fertilization filament. A. transmontanus fertilization can occur at low sperm per egg ratios; however, crossfertilization of A. transmontanus eggs with lake sturgeon, A. fluvescens, sperm results in a very low number of fertilized eggs, even at high sperm per egg ratios. The morphological, physiological, and biochemical phenomenon reviewed in this paper are related to the environment in which they occur. Also, the possible role of the acrosome and the presence of numerous micropyles are discussed.