Shovelnose Sturgeon Research Articles

Habitat Use and Movements of Pallid and Shovelnose Sturgeon in the Yellowstone and Missouri Rivers in Montana and North Dakota

We observed the habitat use and movements of 24 pallid Scaphirhynchus albus and 27 shovelnose S. platorynchus sturgeon in the Yellowstone and Missouri rivers in Montana and North Dakota. Pallid sturgeon used sandy substrate more often than shovelnose sturgeon, as well as greater depths; both species used similar current velocities. Pallid sturgeon used river channels with greater widths, midchannel bars, frequent islands, and subclimax riparian vegetation more often than shovelnose sturgeon. Both species moved up to 15 km/d and moved during all seasons and diel periods, but they moved less during fall and winter; ranges of activity among the most wide-ranging individuals exceeded 250 river kilometers (rkm). Pallid sturgeon used the lower 28 rkm of the Yellowstone River in spring and summer, shifting to the Missouri River below the confluence of the Yellowstone River in fall and winter. Shovelnose sturgeon were most often observed in the Yellowstone River in all seasons. Aggregations in late spring and early summer suggest that pallid sturgeon may spawn in the lower 14 rkm of the Yellowstone River. The infrequent use by both species of the Missouri River from Fort Peck Dam downstream to the Yellowstone River confluence may be due to altered ecological conditions associated with the dam and emphasizes the importance of natural river processes for these species.

Evaluation of Propeller-Induced Mortality on Early Life Stages of Selected Fish Species

Abstract The mortality of ichthyoplankton entrained through a scale model of a towboat propeller was evaluated in a large (>2 million L) circulating water channel. Five species of fish (larval shovelnose sturgeon Scaphirhynchus platorynchus, larval lake sturgeon Acipenser fulvescens, the larvae and eggs of paddlefish Polyodon spathula, larval blue sucker Cycleptus elongatus, and juvenile common carp Cyprinus carpio) were tested. Replicate groups of individuals were subjected to one or more shear stress levels (634, 1,613, 3,058, and 4,743 dynes/cm2 (1 dyne = the force that would give a free mass of 1 g an acceleration of 1 cm/s2). Mortality was a linear function of shear stress for all species and life stages. Paddlefish eggs and common carp juveniles were more resistant to shear stress than all larval fish. Smaller larvae (lake sturgeon and blue suckers) experienced higher mortalities (>75%) than larger larvae (shovelnose sturgeon and paddlefish). The conditional mortality (i.e., treatment less control m...

Seasonal Variation in Sampling Indices for Shovelnose Sturgeon, River Carpsucker, and Shorthead Redhorse Collected from the Missouri River below Fort Randall Dam, South Dakota

ABSTRACT Gill nets and electrofishing were utilized in the Missouri River below Fort Randall Dam, South Dakota to sample river carpsucker (Carpiodes carpio), shorthead redhorse (Moxostoma macrolepidotum), and shovelnose sturgeon (Scaphirhynchus platorynchus). Shorthead redhorse, shovelnose sturgeon, and river carpsucker all exhibited significant monthly variation in mean relative weight (Wr) during at least one sample year (P < 0.05). In general, Wr values for all species tended to be highest early in the year followed by a steady decline to a seasonal low during the later sample months. Shorthead redhorse and river carpsucker catch per unit effort (CPUE) followed a similar bimodal pattern of spring and fall peaks with lower CPUE during summer. Catch per unit effort of shovelnose sturgeon was highest in the fall at the lower site (P < 0.001, October 1998; P = 0.006 and P = 0.009, September and October 1999) with no differences found at the upper site. Within-site variations in size generally were not significant for any species analyzed (P > 0.05). However, the median length of fishes tended to be higher at the upper site during early sample months and higher at the lower site during the later sample months, suggesting a migratory pattern for adult fish.

Reproductive Isolation in Sympatric Populations of Pallid and Shovelnose Sturgeon

Abstract Pallid sturgeon Scaphirhynchus albus and shovelnose sturgeon S. platorynchus are recognized morphologically as separate species. A previous genetic study with allozymes was unable to distinguish between the two species or demonstrate their reproductive isolation in regions of sympatry. Our main objective was to measure the genetic variability within and among populations of pallid and shovelnose sturgeon at the northern and southern extremes of their sympatric ranges to determine if genetic variation within the two species exhibits patterns consistent with reproductive isolation. Additionally, we examined a sample of individuals identified morphologically as hybrids of the two species to determine their genetic relationship to fish identified morphologically as pallid and shovelnose sturgeon. Data from five nuclear DNA microsatellite loci indicated that pallid and shovelnose sturgeon were genetically distinct at three sympatric localities. Pallid sturgeon from two northern populations in the uppe...

Patterns in abundance of fishes in main channels of the upper Mississippi River system

Abundance of fishes of the main channels of the upper Mississippi River system and of other large North American rivers is largely unknown because historic sampling methods have been inadequate. We used a bottom trawl to estimate spatial and temporal patterns in abundance in the navigation channels of Pool 26 of the Mississippi River and the lower Illinois River. Total biomass density averaged 21 and 29 kg·ha–1in the navigation channels of Pool 26 and the lower Illinois River, respectively. We identified spatial and temporal patterns in catches of key species using a generalized linear model based on the negative binomial distribution. Some species, including shovelnose sturgeon (Scaphirhynchus platorynchus), are persistent residents of the main channel. Multiple-season residents, including freshwater drum (Aplodinotus grunniens), rely heavily on the main channel during most of the year but leave it briefly, for example to seek thermal refugia in backwaters during winters. We suggest revision of the prevailing notion that main channels of large temperate rivers serve mainly as corridors for movement among other habitat types.

Phylogenetics ofScaphirhynchusBased on Mitochondrial DNA Sequences

Species delineation and taxonomy within the sturgeon genus Scaphirhynchus is controversial. This issue is made more complex by political issues regarding the Alabama sturgeon S. suttkusi and potential hybridization between sympatric shovelnose sturgeon S. platorynchus and pallid sturgeon S. albus. We investigated phylogenetic relationships among species of Scaphirhynchus based on nucleotide sequences for two mitochondrial loci, cytochrome b and the control region (D-loop). White sturgeon Acipenser transmontanus and green sturgeon A. medirostris were used as outgroups. Phylogenetic analyses did not recover monophyletic shovelnose or pallid sturgeon; however, some populations of pallid sturgeon were resolved as sister to the Alabama sturgeon, and one specimen of shovelnose sturgeon was consistently resolved as the sister to all other ingroup taxa. The hierarchical pattern of relationships produced by analysis of mitochondrial DNA is not consistent with that produced by morphological data. It is consistent with the hypothesis of a low rate of evolution of these genes in Scaphirhynchus and reflects recent hybridization between shovelnose and pallid sturgeon, probably due to habitat degradation.

Microsatellite Analysis of Genetic Variation in Sturgeon: New Primer Sequences forScaphirhynchusandAcipenser

Low levels of genetic variation at traditional molecular markers have hampered genetic research within the family Acipenseridae. In an effort to develop a large set of polymorphic genetic markers, 172 clones were sequenced from three subgenomic libraries of shovelnose sturgeon Scaphirhynchus platorynchus; the libraries were enriched for two dinucleotide and one tetranucleotide microsatellite motifs (CA, GA, and TAGA). Primers were designed for 113 of the sequences and tested against shovelnose sturgeon, pallid sturgeon S. albus, white sturgeon Acipenser transmontanus, lake sturgeon A. fulvescens, and green sturgeon A. medirostris. Of the 113 primer sets tested, 96% amplified in one or more species (58 dimeric and 50 tetrameric). In Scaphirhynchus species, 93% of all loci amplified, and 76% were polymorphic. Within the individual Acipenser species, 65–80% of loci amplified, with 42–58% being polymorphic. Polymorphic systems for Scaphirhynchus species predominately displayed simple, disomic banding patterns, while those for Acipenser species typically displayed banding patterns characteristic of tetraploid or higher polyploid levels. These new microsatellite loci provide a group of genetic markers that are detectable with noninvasive sampling and that should prove useful in the preservation of threatened and endangered sturgeon species worldwide.

Intersexes in Mississippi River shovelnose sturgeon sampled below Saint Louis, Missouri, USA

The Missouri Department of Conservation detected high organochlorine levels in tissues of fish from the Mississippi River south of Saint Louis. Chlordane, which is both a carcinogen and an endocrine disrupter, reached 2960 μg/kg in fillets of shovelnose sturgeon, Scaphirhynchus platyorynchus, and 1926 μg/kg in their roe, wet weight basis. Polychlorinated biphenyls (PCBs) and p,p′-dichlorodiphenyldichloroethylene (DDE) in roe have reached 5810 and 780 μg/kg, respectively. The purpose of this study was to determine if endocrine disrupters and carcinogens are a potential cause of the significantly diminished reproduction capacity and population declines in the endangered pallid sturgeon, Scaphirhynchus albus. Twenty-four surrogate shovelnose sturgeons were sampled north of Saint Louis where contaminant levels were lower compared with 17 sampled south of Saint Louis where contaminant levels were high. Liver and gonad tissues were formalin-fixed, histologically processed and examined. Neoplasms were not found. The principal finding was that the testes of two of the seven downstream male fish contained ovigerous lamellae, in addition to mature sperm. Since sturgeons are gonochoristic and intersexes are rare and unusual, the occurrence of intersex in 29% of the male Mississippi River shovelnose sturgeon examined from a population contaminated with chlordane and other chemicals raise concern for human health, species biodiversity and preservation of waterway quality. These findings, however, need to be corroborated by expanded studies with a higher sample size.

Analysis of motility parameters from paddlefish and shovelnose sturgeon spermatozoa

Ninety to 100% of paddlefish Polyodon spathula were motile just after transfer into distilled water, with a velocity of 175 μm s‐1, a flagellar beat frequency of 50 Hz and motility lasting 4–6 min. Similarly, 80–95% of shovelnose sturgeon Scaphirhynchus platorynchus spermatozoa were motile immediately when diluted in distilled water, with a velocity of 200 μm s‐1, a flagellar beat frequency of 48 Hz and a period of motility of 2–3 min. In both species, after sperm dilution in a swimming solution composed of 20 mM Tris–HCl (pH 8·2) and 20 mM NaCl, a majority of the samples showed 100% motility of spermatozoa with flagella beat frequency of 50 Hz within the 5 s following activation and a higher velocity than in distilled water. In such a swimming medium, the time of motility was prolonged up to 9 min for paddlefish and 5 min for sturgeon and a lower proportion of sperm cells had damage such as blebs of the flagellar membrane or curling of the flagellar tip, compared with those in distilled water. The shape of the flagellar waves changed during the motility phase, mostly through a restriction at the part of the flagellum most proximal to the head. A rotational movement of whole cells was observed for spermatozoa of both species. There were significant differences in velocity of spermatozoa between swimming media and distilled water and between paddlefish and shovelnose sturgeon.

Juvenile pallid ( Scaphirhynchus albus) and hybrid pallid×shovelnose ( S. albus×platorynchus) sturgeons exhibit low physiological responses to acute handling and severe confinement

Following a 7.5-h transport haul, juvenile pallid sturgeon ( Scaphirhynchus albus) showed a small but significant increase in plasma cortisol to 4.7 ng ml −1 but similar increases did not occur after fish were handled in a net held in the air for 30 s. Subsequent experiments on yearling pallid sturgeon and hybrid pallid×shovelnose ( S. albus× platorynchus) sturgeon using the same 30-s handling stressor failed to evoke increases in plasma cortisol, lactate or glucose. Plasma cortisol increased significantly from about 2 to 13–14 ng ml −1 in both pallid and hybrid sturgeon during a 6-h severe confinement stressor with handling. Plasma cortisol in 2-year-old pallid sturgeon subjected to the same stressor demonstrated a linear pattern of increase during the initial 1 h. Plasma lactate increased from 1.11 to about 2.11 mmol l −1 in hybrid sturgeon during the first hour of severe confinement but did not change throughout the entire confinement period in pallid sturgeon. A significant increase in plasma cortisol to 5.4 ng ml −1 in 2-year-old pallid sturgeon 1 h after being subjected to 30 s handling at 19:00 h but not at 07:00 or 13:00 h suggests that a small diurnal variation in their stress response may exist. Although both pallid and hybrid sturgeons were responsive to stress, they exhibited very low physiological responses compared with those following equivalent stressors in most teleostean fishes or another chondrostean, the paddlefish ( Polyodon spathula). Reasons for the apparent low responses to handling and confinement in scaphirhynchid sturgeons are not known but may relate to their evolutionary history, neuroendocrine mechanisms involved in their corticosteroid responses, or anatomy of their interrenal tissue structure.

Genetic distinction of pallid, shovelnose, and Alabama sturgeon: emerging species and the US Endangered Species Act

The sturgeon genus Scaphirhynchus consists of threerecognized species. Pallid and shovelnose sturgeon (S. albusand S. platorynchus, respectively) are sympatric in theMissouri and lower Mississippi Rivers of the central United States. TheAlabama sturgeon (S. suttkusi) is endemic to the nearby MobileRiver drainage and is isolated geographically from the other twospecies. Pallid sturgeon and the extremely rare Alabama sturgeon arelisted as endangered under the US Endangered Species Act (ESA).In contrast, shovelnose sturgeon are relatively common and are notlisted. Despite these taxonomies and morphological evidence, somebiologists have questioned the genetic and taxonomic distinctions of thethree species, thus raising doubts concerning the validity of protectingpallid and Alabama sturgeon under the ESA. To investigate thesequestions, we compared a 436 base-pair sequence of the mitochondrial DNA(mtDNA) control region among the three species. We observed 16 mtDNAhaplotypes defined by 27 single base-pair substitutions (transitions)and one single base-pair insertion/deletion (indel) among 78individuals examined. The maximum sequence divergence among thosehaplotypes (2.06%) was less than values usually observed betweenfish species. However, Alabama sturgeon (n = 3) weredistinguished from the other two taxa (n = 75) by aunique base-pair substitution and haplotype, and pallid and shovelnosesturgeon at their northern range of natural sympatry (upper MissouriRiver) did not share any haplotypes. On the other hand, only frequencydifferences among shared haplotypes distinguished (P < 0.01)pallid and shovelnose sturgeon at their southern range of naturalsympatry (Atchafalaya River), and genetic distances between northern andsouthern localities for each species were nearly as large as thedistances between species. These latter results are consistent withseveral hypotheses, including reports (based on morphology) of putativenatural hybrids in the Atchafalaya River but not in the upper MissouriRiver. Overall, these mtDNA results indicate significant reproductiveisolation between pallid and shovelnose sturgeon in areas of naturalsympatry, and recent evolutionary divergence of Alabama sturgeon. ThesemtDNA results provide the first molecular genetic evidence fordistinguishing the three Scaphirhynchus species and, coupledwith morphological and biogeographic data, indicate that pallid andAlabama sturgeon should be evaluated as distinct species under theESA.

Stranding Potential of Young Fishes Subjected to Simulated Vessel-Induced Drawdown

Abstract During early life stages, fish in the Mississippi River system may become stranded by shoreline drawdowns induced by the passage of commercial vessels. We examined the stranding of larval shovelnose sturgeon Scaphirhynchus platorynchus, paddlefish Polyodon spathula, and bigmouth buffalo Ictiobus cyprinellus and of juvenile blue catfish Ictalurus furcatus, largemouth bass Micropterus salmoides, and bluegill Lepomis macrochirus in a laboratory flume. Stranding was measured at three vertical drawdown rates (0.76, 0.46, and 0.21 cm/s) and two bank slopes (1:5 and 1:10). Blue catfish, shovelnose sturgeon, and paddlefish were not tested at both bank slopes. Susceptibility to stranding varied among species and was independent of drawdown rate. At a slope of 1:5, shovelnose sturgeons had the highest stranding percentage (66.7%), followed by paddlefish (38.0%), bluegills (20.0%), bigmouth buffalo (2.2%), and largemouth bass (0.0%). At 1:10, blue catfish had the highest stranding percentage (26.7%), follow...

Overwinter Habitat Use of Shovelnose Sturgeon in the Kansas River

Overwinter habitat use of shovelnose sturgeon Scaphirhynchus platorynchus in the Kansas River was determined by radiotelemetry from November 1996 to March 1997 at water temperatures of 2–9°C. Eighty percent of the shovelnose sturgeon locations were in water depths of 1.0–2.0 m, where current velocities were 0.01–1.11 m/s at the surface and 0.02–0.79 m/s at the bottom. Depths and surface current velocities at fish locations were positively related to discharge (r = 0.47, P = 0.0001; r = 0.60, P = 0.0001, respectively); bottom current velocities were not significantly correlated (r = 0.08, P = 0.31) with discharge. Water depths, surface current velocities, and bottom current velocities were not significantly related to water temperature (P > 0.05). Ninety-two percent of the shovelnose sturgeon locations were over sand substrate. Inside-bend macrohabitats were used in proportion to their abundance (P > 0.05), whereas channel crossovers were used in greater proportion than their availability (P ≤ 0.05); outside-bend habitats were avoided (P ≤ 0.05). During high discharge (>150 m3/s), shovelnose sturgeon appeared to move near shore or downstream of instream cover. Most shovelnose sturgeon moved less than 2 km during the study period, but one fish moved more than 8 km. Movement (km/d) and directional movement (i.e., upstream or downstream) were not related to discharge or water temperature (P > 0.05). These data indicate that shovelnose sturgeon use channel-crossover macrohabitats and areas with bottom velocities of 0.02–0.79 m/s, independent of discharge. In addition, it appears that shovelnose sturgeon do not congregate in deep areas at water temperatures less than 9°C.

The photoreceptors and visual pigments of two species of Acipenseriformes, the shovelnose sturgeon ( Scaphirhynchus platorynchus ) and the paddlefish ( Polyodon spathula )

Scanning electron microscopy, microspectrophotometry, and spectrophotometry of digitonin extracts were employed to characterize the photoreceptors and visual pigments of two freshwater Acipenseriformes. The retinas of the shovelnose sturgeon, Scaphirhynchus platorynchus (Acipenseridae), and the paddlefish, Polyodon spathula (Polyodontidae) are dominated by large rods with long, broad outer segments. A second rod, rare and much narrower than the dominant rod, is present in Scaphirhynchus but not seen in Polyodon. The absorbance maximum of the visual pigment in the rods of Polyodon is near 540 nm; that of Scaphirhynchus near 534 nm. The retinas of both species contain substantial numbers of large, single cones, about 33% of the photoreceptors in Scaphirhynchus; 37% in Polyodon. Scaphirhynchus cone pigments have absorbance maxima near 610 nm, 521 nm and 470 nm, respectively. Polyodon cone pigments absorb maximally near 607 nm and 535 nm, respectively. All visual pigments are based on vitamin A2. The data are compared to those from other Acipenseriformes and are discussed in terms of lifestyle and behavior.

Purification and Characterization of Galanin and Scyliorhinin I from the Hybrid Sturgeon,Scaphirhynchus platorynchus×Scaphirhynchus albus(Acipenseriformes)

The sturgeons (order Acipenseriformes) are extant representatives of a group of ancient Actinopterygian (ray-finned) fish. Galanin and scyliorhinin I (a tachykinin with limited structural similarity to mammalian substance P) have been isolated from an extract of the gastrointestinal tract of a sturgeon (an F1 hybrid between the shovelnose sturgeon,Scaphirhynchus platorynchus,and the pallid sturgeon,Scaphirhynchus albus). The primary structure of sturgeon galanin (Gly-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu10-Leu-Gly-Pro-His-Ala-Val-Asp-Gly-His-Arg20-Ser-Leu-Ser-Asp-Lys-His-Gly-Leu-Pro·NH2) contains only two amino acid substitutions (Ser23→ Asn and Pro29→ Ala) compared with galanin from the bowfin,Amia calva(Amiiformes), but five amino acid substitutions compared with galanin from the trout (Teleostei). Similarly, the sturgeon tachykinin (Ser-Lys-Tyr-His-Gln-Phe-Tyr-Gly-Leu-Met·NH2) contains only one amino acid substitution (Tyr3→ Ser) compared with scyliorhinin I previously isolated from bowfin stomach but five amino acid substitutions compared with trout substance P. The data support the hypothesis that the Acipenseriformes and the basal Neopterygians (gars and bowfin) share a close phylogenetic relationship.

Standard Weight (Ws) Equation and Length Categories for Shovelnose Sturgeon

Abstract Weight–length data were compiled from 32 populations of shovelnose sturgeon Scaphirhynchus platorynchus (N = 11,820) from nine states within the geographic distribution of the species. We used the regression-line-percentile technique, which provides a 75th-percentile standard, to develop the standard weight (Ws ) equation. The proposed equation in metric units is log10 Ws = −6.287 + 3.330 log10FL; Ws is weight in grams and FL is fork length in millimeters. The equivalent equation in English units is log10 Ws = −4.266 + 3.330 log10FL; Ws is weight in pounds and FL is fork length in inches. These equations are proposed for use with shovelnose sturgeon between 120 mm (5 in) and 1,050 mm (41 in). Values for relative weight (Wr ) calculated with the Ws equation did not consistently increase or decrease with increasing fish length, indicating absence of length bias. We propose the following length categories for calculation of proportional stock density (PSD) and relative stock densities (RSDs): stock,...

Age, Growth, and Mortality of Shovelnose Sturgeon in the Lower Mississippi River

Two hundred of 295 shovelnose sturgeon Scaphirhynchus platorynchus captured in the Mississippi River near Rosedale and Vicksburg, Mississippi, were aged by examining sectioned pectoral fin rays. Ages ranged from 2 to 16 years, and the annual mortality was 20% for ages 7 and greater. The weight (W, g), to fork length (FL, mm) relation was W = 0.000001257 FL3.174 (R2 = 0.87). The von Bertalanffy growth equation for fork length was FL = 730(1 − e−0.213(t+0.972)); the equation for weight was W = 1,604(1 − e−0.148(t−1.841)). Mortality and mean length at age were less than has been reported for upper Mississippi River populations of shovelnose sturgeon. Knowledge of causes of mortality of shovelnose sturgeon may have applications in management of the sympatric pallid sturgeon Scaphirhynchus albus.

Purification and Cardiovascular Activity of [Met 1, Met 5]-Bradykinin from the Plasma of a Sturgeon (Acipenseriformes)

The sturgeons (Order Acipenseriformes) are extant representatives of a group of primitive Actinopterygian (ray-finned) fish that probably shared a common ancestor with present-day teleosts. Incubation of heat-denatured plasma from a sturgeon (a hybrid of the shovelnosed sturgeon Scaphirhynchus platorynchus and the pallid sturgeon Scaphirhynchus albus) with either trypsin or porcine pancreatic kallikrein generated bradykinin-like immunoreactivity. The primary structure of sturgeon bradykinin was established as Met-Pro-Pro-Gly-Met-Ser-Pro-Phe-Arg. This amino acid sequence contains two amino acid substitutions (Arg 1 → Met and Phe 5 → Met) compared with mammalian bradykinin. Bolus injections of synthetic sturgeon bradykinin in doses as low as 1 pmol/kg into the dorsal aorta of unanesthetized sturgeon resulted in an immediate and significant fall in arterial blood pressure with a maximum depressor response at 300 pmol/kg. Thus, the cardiovascular response of the sturgeon to bradykinin resembles more closely the response of mammals rather than the predominantly pressor response seen in teleost fish. Sturgeon bradykinin produced a strong and concentration-dependent (EC 50 = 4.7 ± 0.7 × 10 −10 M) relaxation of rings of vascular tissue from the sturgeon ventral aorta that had been pre-contracted with acetylcholine. The data indicate that sturgeon tissues are particularly responsive to native bradykinin and suggest that the kallikrein–kinin system may have evolved before the appearance of the neopterygians (gars, bowfin and teleosts).

Induced meiotic gynogenesis in shovelnose sturgeon

Gynogenesis was induced in three shovelnose sturgeon (Scaphirhynchus pIatorynchus) by heat shock after egg activation with UV-treated paddlefish (Polyodon spathula) milt. Ultraviolet dosage (J m−2) for the pooled milt samples was calculated using the following linear regression equation: Dosage = 2405.27 − 352.80X 19.78X2 (X = percent transmittance of milt). Activated eggs were incubated at 18 °C until shocking at 35 °C. Shock duration was applied at 0.05τ0 intervals from 0.15 to 0.40 τ0 (8.25 to 22.00 min post-fertilization; τ0 at 18 °C = 55 min). The highest yield of gynogenotes (16%) was observed at 0.25 τ0 for female 3, 10 % at 0.30 τ0 for female 2 and 12% at 0.35 τ0 for female 1. The percentage of viable gynogenotes responded quadratically to the tau index (τs/τ0) when shock treatments were applied. The higher yields of viable diploid sturgeon gynogenotes were achieved when eggs were heat shocked at embryological ages ranging from 0.25 to 0.35 τ0 (approximately 14 to 19 min post-activation at 18 °C). No viable hybrids were produced in the control fertilization of sturgeon eggs with intact paddlefish sperm which verified the gynogenetic origin of the offspring produced. © Rapid Science Ltd. 1998

Induced Meiotic Gynogenesis of Paddlefish Polyodon spathula

AbstractViable, diploid gynogenetic (gynogenotes) paddlefish Polyodon spathula were produced by activating eggs with ultraviolet‐irradiated shovelnose sturgeon Scaphirhynchus platorynchus spermatozoa and heat shocking. Without irradiation treatment, sturgeon spermatozoa appeared to activate the eggs (up to gastrulation), but did not result in any viable hybrids. Experiment 1 determined that heat‐shock treatment of 35 C for a 2‐min duration within the interval of 2–22 min post‐activation resulted in highest yield of gynogenotes (12–19%) from eggs incubated at 18 C. Experiment 2 applied the heat shock treatment at 35 C from 14.0 to 28.0 min in 2‐min intervals after activation at 18 C for a larger scale of gynogenetic production. Both experiments showed that the best yields of gynogenotes were obtained when the heat shock treatment occurred at 16, 18, and 20 min after activation. When these times were expressed in terms of τ0. units (duration of one mitotic cycle of synchronous cell division related to water temperatures), optimal activations were 0.26, 0.29, and 0.32τ0 (τ0@ 18 C = 63.5 min). Experiment 3 tested the utility of τ0. at two different pre‐shock incubation water temperatures of 18 C and 16 C, and determined that there was no significant interaction in percentage of viable gynogenotes between two different incubation temperatures and the mitotic intervals (0.21, 0.26, 0.31, 0.36, 0.41τ0) tested. Best survival of gynogenotes occurred when eggs held at either pre‐shock incubation water temperatures were shocked at 0.26τ0 All gynogenotes examined were histologically confirmed to have ovarian tissue and were determined to have similar oocyte development to that of normal female (control) paddlefish.