Comparative precision of age estimates from two southern reservoir populations of paddlefish [Polyodon spathula (Walbaum, 1792)]

The aim of the study was to determine whether location and sex affected the age precision estimates between two southern, reservoir populations of paddlefish [Polyodon spathula (Walbaum, 1792)]. From 589 paddlefish collected in Grand Lake and Keystone Lake, Oklahoma in 2011, ages from dentaries were estimated using three independent readers and precision was compared with coefficient of variation between locations and sexes. Ages were more precisely estimated from Grand Lake and from females.     

Paddlefish (Polyodon spathula) in Europe: An aquaculture species and a potential invader

The paddlefish (Polyodon spathula) was first introduced to Europe in 1974, mainly due to its potential for rearing in natural polyculture ponds and large temperate reservoirs. The information on the history of paddlefish aquaculture efforts in Europe is scarce, as well as data on current paddlefish aquaculture status and trends. In addition, there is a lack of data on its presence and potential establishment in the wild, while its invasive potential and associated risks and impacts are largely unknown. In order to evaluate its current status in Europe, we conducted a survey among scientists, aquaculture producers and other stakeholders, and reviewed literature and data on the Internet. Based on the results obtained, we discuss the potential and the challenges in European paddlefish aquaculture development, and analyze paddlefish invasive potential and risks associated with its naturalization. Paddlefish aquaculture is well established only regionally in Europe, but offers relatively high potential for further development in pond farms. Nevertheless, future development will require careful planning, especially regarding market development and improved marketing strategies. While paddlefish likely represents a low‐risk invader, improved control and reporting on trade and intentional and unintentional releases will be required. Given the lack of knowledge on potential impacts following its introduction, due caution seems highly advisable.     

Lipid acquisition and retention in tissues of spawning adult paddlefish Polyodon spathula (Walbaum, 1792) in relation to extended and compressed life history patterns in two river‐reservoir systems

Data from recreationally caught adult paddlefish from North Dakota and Oklahoma, USA, was used in an initial attempt to explain variation in lipid content in adult wild paddlefish Polyodon spathula (Walbaum, 1792) by stock and by sex. The objectives of this study were to describe the relative importance of three distinct paddlefish tissues [white muscle, red muscle, and gonadal fat body (GFB)] for lipid storage, and compare lipid content of these tissues between stock and sex. It was hypothesized that lipid content of the three tissue types would be related to each other within individual fish; and that, consistent with previously documented life history differences, lipid concentrations for all tissues would be sex‐ and stock‐specific. Paddlefish were sampled in April and May 2012 from the Grand Lake, Oklahoma, USA (GL) and Yellowstone‐Sakakawea, North Dakota (SAK) stocks. Three tissue types were collected from SAK fish, including white muscle (N = 137; 83M, 54F), red muscle (N = 74; 36M, 38F), and GFB (N = 164; 105M, 59F). Samples from GL fish included white muscle (N = 60; 36M, 24F), and GFB (N = 42; 41M, 1F). Proximate analysis was used to quantify the percentage of lipid, water, ash, and protein in tissue samples. The lipid component of proximate analysis was completed using the ANKOM method of lipid extraction which uses heated petroleum ether to extract lipid. Also investigated were lipid accumulation and storage in adult paddlefish in relation to tissue type: white muscle, red muscle, gonadal fat bodies (GFB) within individual fish, between the sexes, and between the two different stocks. White muscle was significantly correlated with both red muscle and GFB lipid, but red muscle lipid was not significantly correlated with GFB lipid. White muscle lipid content differed by stock and sex, with the more northerly stock having higher lipid content than the more southerly stock. Females had higher white muscle lipid content (SAK F = 17.18, M = 9.09; GL F = 6.74, M = 4.99) and red muscle (SAK F = 47.72, M = 30.93) than males. In contrast, GFB lipid differed by sex but not stock, with females having lower lipid content (SAK = 79.79, GL = 89.08) than males (SAK = 89.08; GL = 91.72). Life history differences, growing season, and the role of metabolism may help explain the differences in concentrations of lipids observed between stocks and between the sexes for all three tissues. It was hypothesized that different tissues may be used for different metabolic processes and that although metabolism likely strongly influences muscle tissue lipid, GFB lipid is probably linked more closely to reproductive demands associated with gonad development.     

First report of intersex in a lutjanid: the goldband snapper Pristipomoides multidens

This is the first report of intersex in a lutjanid species, the goldband snapper Pristipomoides multidens, in which the gonads of a male fish contain multifocal oocytes scattered among testicular tissue. The incidence rate of intersex was low (<1.0%), with oocytes observed in the testes of only two of 206 male fish examined. The capacity for P. multidens to develop an intersex condition suggests that future monitoring of this species should include histological analysis of gonads.     

Modelling bioenergetic and population-level impacts of invasive bigheaded carps (Hypophthalmichthys spp.) on native paddlefish (Polyodon spathula) in backwaters of the lower Mississippi River

1. While invasions of large rivers by exotic fish species are well documented, assessing actual or potential impacts on native species is a challenge. Rapid assessments may be possible through the application of a combination of bioenergetic and population dynamic models.
2. Paddlefish (Polyodon spathula) is a native species in the central USA with a history of population decline due to waterway development and overharvesting for roe. It is not known whether paddlefish are impacted by resource competition from invasive bigheaded carp populations, including silver (Hypophthalmichthys molitrix) and bighead carp (Hypophthalmichthys nobilis), which have expanded dramatically in the Mississippi River.
3. We used bioenergetic models to project the potential impact of invasive silver and bighead carp on zooplankton density and paddlefish somatic growth in backwater habitat. Bioenergetic outputs were translated to impacts on fecundity, becoming inputs for 50-year metapopulation simulations of backwater habitat connected to the main-stem Mississippi River by episodic flood events.
4. Competition with carp reduced growth and increased the risk of population decline for paddlefish. Impacts increased disproportionately with increased carp abundance and were further exacerbated in scenarios with increased diet overlap or decreased zooplankton abundance.
5. We also analysed paddlefish condition data collected at sites near the lower Mississippi River with varying histories of carp invasion. These data give credence to the bioenergetic model output; paddlefish had reduced body condition at sites with long-established, high-density carp populations.
6. We conclude that invasive bigheaded carps have great potential to reduce paddlefish growth, fecundity, and abundance. The pairing of bioenergetics and population models is likely to be broadly useful in assessing the risks posed by other invasive species.

     

Intersex and male development in Daphnia magna

Sex induction is environmentally stimulated in Daphnia and involves a cue-dependent response for sex determination. Somatic growth was shown to be similar in males and females during juvenile instars, but divergent due to a reduction in male somatic growth, at about the time that females produce ovaries. At this time, males appeared morphologically adult with respect to secondary sex characteristics. Intersex was rare and is unlikely to be important in natural populations. Intersex could be induced in both sexes, and observed more frequently after longer exposure to high temperature, or in the second generation following a temperature change. This indicates an impact on the ability of mothers to determine the sex of the offspring. It may be possible to use intersex characteristics for manipulative investigation of sex-determination mechanisms in Daphnia. Although sex-determination is initiated before birth, intersex occurrence suggests that development of male characters requires an additional process, probably involving hormone activity, during juvenile development and maturation.     

Energy acquisition and retention by age‐0 and age‐1 paddlefish Polyodon spathula (Walbaum, 1792) in relation to size,growth, and rearing conditions in two Great Plains reservoirs and hatchery ponds

The objective of this study was to investigate lipid accumulation and storage in age‐0 and age‐1 paddlefish Polyodon spathula (Walbaum, 1792) in relation to age, stock, year, and growth. Juvenile paddlefish were collected from three locations in North Dakota and Montana, USA, during July and August of 2011 and 2012 and proximate analysis was used to determine lipid content. RNA/DNA ratios were used as an index of growth rates. Differences in age‐based lipid accumulation and storage in juvenile paddlefish suggest a split allocation between growth and lipid storage, with growth being the highest initial priority and emphasis on energy storage occurring at a larger size, later in life. Differences in lipid allocation between stocks indicate that allocation is influenced by hatchery/wild rearing conditions. Differences within and between year‐classes are consistent with field evidence observed in 2012 of a strong 2011 year‐class, and indicate that during productive times, paddlefish may allocate energy to both body growth and lipid reserves, and that allocation differs among years. The lack of a relationship between RNA/DNA ratio and lipid does not support a physiologically exclusive allocation strategy between growth and lipid. Evidence from this and other studies suggests rather that an emphasis on growth, some energy storage, and a large rostrum size in relation to overall fish length in age‐0 and age‐1 fish, may be adaptive in avoiding predation while accruing necessary energy reserves for overwintering. Although this study also provides reference information regarding proximate composition of wild and hatchery origin juvenile paddlefish, much more study is needed into the relationships among growth, low and high lipid groups, lipid allocation in juvenile paddlefish as well as the existence and timing of allocation changes between growth and storage. To aid in understanding paddlefish survival and year‐class strengths, these relationships also need to be linked to inter‐annual differences in early rearing environments for age‐0 and age‐1 fish.     

Exploitation of paddlefish Polyodon spathula (Walbaum, 1792) in the Mississippi River

Concern over exploitation rates of the American paddlefish Polyodon spathula from sport and commercial fisheries has increased in recent decades and the Convention on International Trade of Endangered Species is now seeking information from state agencies regarding the sustainability of commercially harvested paddlefish populations. The Missouri Department of Conservation is addressing this through the implementation of a 5‐year tagging study on exploitation of paddlefish in the Mississippi River. The first 2 years of this project found that minimal exploitation of paddlefish along Missouri's eastern border was equal to 4.01% (SE = 0.02). After updating previously constructed spawning potential ratio modeling completed in 2016 with the more accurate estimates of exploitation determined in this study it becomes apparent that paddlefish populations of the Mississippi River are currently at sustainable levels. However, precautionary adjustment of regulations is advised to protect paddlefish through maturation and to counteract the possibility of increased harvest intensity resulting from increased demand of domestic caviar.     

Ecology and biology of paddlefish in North America: historical perspectives,management approaches,and research priorities

Paddlefish (Polyodon spathula, Polyodontidae)are large, mostly-riverine fish that once wereabundant in medium- to large-sized river systemsthroughout much of the central United States. Concernfor paddlefish populations has grown from a regionalfisheries issue to one of national importance for theUnited States. In 1989, the U.S. Fish and WildlifeService (USFWS) was petitioned to list paddlefish asa federally threatened species under the EndangeredSpecies Act. The petition was not granted, primarilybecause of a lack of empirical data on paddlefishpopulation size, age structure, growth, or harvestrates across the present 22-state range. Nonetheless,concern for paddlefish populations prompted the USFWSto recommend that paddlefish be protected through theConvention on International Trade in EndangeredSpecies of Wild Fauna and Flora (CITES). The additionof paddlefish to Appendix II of CITES, which wasapproved in March 1992, provides a mechanism tocurtail illegal trade in paddlefish and their partsand supports a variety of conservation plans. Paddlefish populations have been negatively affectedby overharvest, river modifications, and pollution,but the paddlefish still occupies much of its historicrange and most extant populations seem to be stable. Although many facets of paddlefish biology andecology are well understood, the lack of informationon larval and juvenile ecology, mechanisms thatdetermine recruitment, population size and vitalrates, interjurisdictional movements, and the effectsof anthropogenic activities present significantobstacles for managing paddlefish populations. Questions about the size and structure of localpopulations, and how such populations are affected bynavigation traffic, dams, and pollution are regardedas medium priority areas for future research. Theavailability of suitable spawning habitat and overallreproductive success in impounded rivers are unknownand represent critical areas for future research. Research on reproductive and recruitment success inimpounded rivers have significant implications formanaging paddlefish, as rivers are modified furtherfor human use.     

An approach for assessing paddlefish Polyodon spathula (Walbaum, 1792) populations using mark‐recapture information

Historically, management of fish populations has been achieved through the use of age‐derived estimates of growth and mortality. For long‐lived species such as the paddlefish, Polyodon spathula, the validation of calcified structures is necessary to correct for the presence of false annuli or the absence of growth rings. Regardless, numerous studies on paddlefish populations throughout their range have continued the use of un‐validated age estimates to evaluate dynamic rate functions. The use of mark‐recapture studies has been applied widely to evaluate growth of short‐lived fishes, but only recently to a few long‐lived freshwater fishes (i.e. white sturgeon, shovelnose sturgeon, and pallid sturgeon). This study provides the first simultaneous evaluation of both mark‐recapture and age‐estimate information in determining population characteristics for paddlefish. In doing so, this study has determined that the P. spathula population in the Black River below Clearwater Dam, Missouri is sustainable. Additionally, mark‐recapture information is sufficient to produce accurate and reliable assessments of paddlefish populations in lieu of validated aging structures; future management should be centered on accurate scientific methods, which is not the case when using un‐validated aging structures (e.g. scales, otoliths, fin rays, dentary bones) to determine population parameters. Mark‐recapture information can provide an accurate, alternative source of growth and mortality information for use in evaluating and managing paddlefish populations throughout their range.     

Intersexuality in the amphipod Gammarus duebeni results from incomplete feminisation by the vertically transmitted parasitic sex ratio distorter Nosema granulosis

We investigated the effects of parasitism and temperature on the production of intersexes in the amphipod Gammarus duebeni from a field population at Cumbrae, Scotland. There was significant temporal variation in intersex frequency which ranged from 0.5 to 5.2% in monthly field collections. Prevalence of Nosema granulosis, a feminising microsporidian parasite, also varied temporally and there was a significant correlation between parasite prevalence and intersex frequency in the field. Intersexes (16.3 ± 0.4 mg) were larger than true females (14.8 ± 0.1 mg) but produced fewer eggs thus demonstrating a cost of intersexuality. Intersexes were less likely to be paired than true females. In a breeding experiment, only females infected by N. granulosis produced intersex offspring. Temperature had no effect on intersex frequency. Intersexes therefore appear to be the result of incomplete feminisation by N. granulosis in this population. These results contrast with previous studies of G. duebeni from different populations which found that intersexes were the result of abnormal development under environmental sex determination. We suggest that intersexuality may be induced by both environmental and parasitic factors in populations of G. duebeni. This revised version was published online in August 2006 with corrections to the Cover Date.     

Altered sexual maturation and gamete production in wild roach (Rutilus rutilus) living in rivers that receive treated sewage effluents.

Disruption in gonadal development of wild roach living in U.K. rivers receiving large volumes of treated sewage effluent is manifest in a variety of ways, ranging from malformation of the germ cells and/or reproductive ducts to altered gamete production. Intersex fish were also found to have an altered endocrine status and an elevated concentration of plasma vitellogenin. Gonadal growth was inhibited only in severely intersex fish, whereas progression of spermatogenesis was delayed in a large proportion of all intersex and exposed male fish. In contrast to the effects observed in the intersex and exposed male fish, the maturation of ovaries in female fish inhabiting effluent-contaminated rivers appeared to be less obviously affected, although a higher incidence of oocyte atresia was found in the effluent-exposed fish compared with the reference fish. A positive correlation was found between the proportion of female tissue in the gonads of intersex fish and their plasma vitellogenin concentration, suggesting that vitellogenin can be an indicator for the level of gonadal disruption in intersex roach. The estradiol-17beta concentration in intersex fish was intermediate between the concentration found in males and females, and the plasma testosterone was between 2- and 3-fold higher in intersex fish compared with male fish. These data suggest a link between altered endocrine status in intersex and female fish and gonadal disruption. Spermiation was also affected in roach living in effluent-impacted rivers: a lower proportion of fish were found releasing sperm, and in those intersex fish that were spermiating, a reduced milt volume and a reduced sperm density were found. All intersex fish had malformations of the reproductive duct(s), and in severely affected fish, the ducts were occluded, thus preventing release of gametes. In view of the widespread occurrence of intersexuality in wild fish populations in rivers throughout the United Kingdom, assessment of the reproductive capabilities of these intersex roach is clearly needed to understand the impact of this phenomenon on roach fertility.     

Fort Peck paddlefish population survival and abundance in the Missouri River

Excessive fishing pressure can induce population declines or complete collapse of fisheries. Unless commercial and recreational fisheries for K-selected fishes, or those with slow growth and late maturation, are carefully managed, declines in abundance or fishery collapse is probable. Paddlefish Polyodon spathula,are a K-selected species that experienced historical declines in abundance as a result of habitat degradation and overfishing. Mark-recapture studies are well-suited for long-lived fishes by providing information on population density and vital rates. For sustainable commercial or recreational fisheries targeting species such as the paddlefish, managers require accurate estimates of population vital rates including survival, abundance, and exploitation. We used a Montana Fish, Wildlife & Parks (MFWP) mark-recapture dataset and modified Jolly-Seber (POPAN) models to estimate survival, recapture, probability of entry, and abundance of 8,518 tagged paddlefish over a 25-year period. With many supporting estimates including stable survival (0.92 for females, mean of 0.82 for males), low exploitation rates (means of 2.6% for females and 2.9% for males), and stable abundance estimates (25-year mean of 12,309 individuals for both sexes), the Fort Peck paddlefish population appears to be stable and well-managed over the past 25 years. Presently, this is the only study focused on paddlefish in North America that has estimated survival and abundance for both male and female paddlefish using contemporary analyses. This research provided a unique opportunity to highlight that the effort exerted by management agencies to collect long-term field data is extremely useful to our understanding of fish populations and management.     

Intersex Frogs Concentrated in Suburban and Urban Landscapes

The occurrence of intersex characteristics in amphibians has been linked to pesticide exposure in the laboratory and proximity to agricultural activity within natural populations. But, overall, the ecology of amphibian intersex is poorly known and, specifically, its occurrence in many landscape types and regions is unstudied. We offer the first analysis of the frequency of amphibian intersex across a range of land covers representing the major landscape types within a region. We used remotely sensed information to characterize land cover surrounding 4774 potential sampling locations within the Connecticut River Valley. From among these, we selected 24 ponds to collect postmetamorphic green frogs (Rana clamitans) from four land cover types: undeveloped, agricultural, suburban, and urban. Collected males were preserved and, then, prepared gonadal tissue samples were screened for the presence of testicular oocytes. A total of 233 animals was examined. Thirteen percent of all male green frogs had gonads containing testicular oocytes. Sexual abnormalities were not randomly distributed among sites or landscape types. Suburban landscapes had the highest frequency of abnormalities (21%), and both suburban and urban land covers were positively associated with the presence of abnormalities within a population. There was no evidence of a positive association with agricultural land cover. Examination of amphibian intersex across a range of contexts reveals that developed landscapes may be hotspots for abnormal sexual development. This new finding suggests that other mechanisms, not previously considered, could contribute to intersex in natural amphibian populations.     

TBT effects on the female genital system of Littorina littorea: a possible indicator of tributyltin pollution

Specimens of the prosobranch Littorina littorea (L., 1758) collected along the East Frisian North Sea coast in summer 1993 exhibited alterations of the pallial oviduct termed as intersex in response to tributyltin (TBT) pollution. The range of TBT body burden was between 150.9 and 1289.5 μg as Sn kg⁻¹ (dry wt.). Five stages of intersex development (0–4) could be distinguished and are documented with scanning electron micrographs. In stages 2–4, which can be found in the direct vicinity of harbours and marinas, the morphological malformations of the oviduct inhibit successful copulation and capsule formation, resulting in sterilization. The intersex index (ISI, calculated as the average intersex stage of a population) and the average prostate length of females were used as parameters for the determination of intersex intensities in the populations. Both indices show significant and positive correlations to the TBT body burden of L. littorea and are promising parameters for TBT biomonitoring. A comparison of TBT bioconcentration factors with populations from England and France indicates that the threshold concentration for intersex development is in the range of 15 ng TBT as Sn/l. Morphometric analyses of the midgut gland revealed no significant differences between sampling stations. In the ovary a retardation and blockage of maturation (atresia) was observed in populations close to harbours. Lytic processes in ovary follicles were observed not only at TBT exposed sites but also at reference stations.     

The American Paddlefish Genome Provides Novel Insights into Chromosomal Evolution and Bone Mineralization in Early Vertebrates

Sturgeons and paddlefishes (Acipenseriformes) occupy the basal position of ray-finned fishes, although they have cartilaginous skeletons as in Chondrichthyes. This evolutionary status and their morphological specializations make them a research focus, but their complex genomes (polyploidy and the presence of microchromosomes) bring obstacles and challenges to molecular studies. Here, we generated the first high-quality genome assembly of the American paddlefish (Polyodon spathula) at a chromosome level. Comparative genomic analyses revealed a recent species-specific whole-genome duplication event, and extensive chromosomal changes, including head-to-head fusions of pairs of intact, large ancestral chromosomes within the paddlefish. We also provide an overview of the paddlefish SCPP (secretory calcium-binding phosphoprotein) repertoire that is responsible for tissue mineralization, demonstrating that the earliest flourishing of SCPP members occurred at least before the split between Acipenseriformes and teleosts. In summary, this genome assembly provides a genetic resource for understanding chromosomal evolution in polyploid nonteleost fishes and bone mineralization in early vertebrates.     

THE OCCURRENCE AND BEHAVIOR OF B-CHROMOSOMES IN ASTRANTHIUM INTEGRIFOLIUM (COMPOSITAE)

Plants of Astranthium integrifolium (Michx.) Nutt. from Oklahoma proved to have a large B-chromosome which was morphologically similar to the smaller A-chromosomes. It was eliminated from some of the progeny of selfed plants. Structural modifications in the B-chromosome were observed. These observations are compared with ones obtained by previous workers, both for this species and in other genera.     

A histological description of intersexuality in the roach

This paper is an illustrative guide to intersex in the roach Rutilus rutilus , based on 150 intersex individuals. Most intersex roach had female germ cells, or oocytes, within a predominantly male gonad (testis), and/or malformed/intersex reproductive ducts. The number, pattern and developmental stage of oocytes within testicular tissue in intersex fish varied greatly. In most intersex fish, a few primary oocytes, or numerous primary and secondary oocytes, were scattered randomly throughout the testicular tissue (multifocal intersex). In other, more severely feminized individuals, large areas of ovarian tissue were separated clearly from testicular tissue (focal intersex). Almost all intersex individuals had a female-like reproductive duct (ovarian cavity). In mild cases of intersex (in which the majority of the germ cells were male) the ovarian cavity was present together with the male sperm duct/vas deferens, whilst in certain severe cases, the sperm duct was absent or vestigial.     

Investigation of some characteristics of enzymes effecting the process of membrane digestion in the paddlefish <Emphasis Type="Italic">Polyodon spathula</Emphasis>

For the first time, a complex investigation of characters of some enzymes effecting the membrane hydrolysis of food in the paddlefish Polyodon spatula is made. The zone of optimum values of temperature of alkaline phosphatase, maltase, and casein-lytic proteinases of the intestinal mucosa is determined within the range from 50 to 60°C, in α-amylase it is shifted towards lower temperatures—10–30°C. A high thermal stability is noted in all investigated enzymes. The maximum level of activity for α-amylase, alkaline phosphatase, and maltase of the intestinal mucosa in the paddlefish Polyodon spatula is within pH 7–9, 9–10, and 6–8, respectively; for casein-lytic proteinases the optimum is at pH 11. In the paddlefish Polyodon spatula, the interaction of nutrients and enzymes of the intestinal mucosa may cause a significant change in the activity level of the enzymes.