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.     

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.     

Characteristics of sperm acrosin-like activity of paddlefish (Polyodon spathula Walbaum)

Spermatozoa of paddlefish and sturgeon fishes (Acipenseriformes), unlike teleost fish, have an acrosome. The objectives of this study were to characterize acrosin-like activity of cryopreserved sperm of paddlefish (Polyodon spathula) and to test and compare stability of paddlefish acrosin-like activity with that of lake sturgeon and bull spermatozoa. Mean acrosin-like activity of cryopreserved paddlefish sperm was 0.372 +/- 0.067 microU/10(6) spermatozoa. This activity was 79% higher in the whole semen than in spermatozoa. Highest activity was recorded at pH 8.0 and 8.5. Triton X-100, zinc ions and 4'-acetamidophenyl 4-guanidinobenzoate (AGB) inhibited the activity. Amidase activity was also inhibited by N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and N-tosyl-L-phenylalanine chloromethyl ketone (TPCK). TLCK at concentrations of 0.1 and 1.0 mM gave a significant decrease in activity of 19 and 61%, respectively. However, TPCK significantly inhibited amidase activity (by 19%) only at concentration 1.0 mM. After acidification and 60 min incubation at 4 degrees C of sperm suspensions only 4% of the activity was retained. A similar phenomenon was observed in the case of lake sturgeon but not bull sperm. These results suggest that trypsin-like activity of Acipenserid fish resembles rather fish trypsin that mammalian one. In frozen-thawed paddlefish sperm a minute chymotrypsin-like activity was also indicated, when GPNA was used as substrate. This activity amounted to 0.0415 +/- 0.0138 microU/10(6) spermatozoa and was 18% of total amidase activity. This suggests that chymotrypsin-like activity may also be present in paddlefish spermatozoa.     

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.     

The integument of the paddlefish,Polyodon spathula

The integument of the paddlefish (Polyodon spathula) is unusual as a relatively small amount of mucus is produced by epithelial cells that are not modified into regular mucous gland cells. A thick compact epidermis and dermis compensate for the slight amount of mucus secreted. Paddlefish have a variety of scales formed of concentric bony lamellae containing osteocytes. There are five kinds of scales: dorsal and ventral fulcra on the caudal fin, rhomboidal scales on the caudal lobe, horny denticles over the pectoral girdle, calcareous denticles on the trunk, and anchor-shaped plates on the rostrum. Except for the fulcra, the scales are undoubtedly vestigial. The numerous surface pits on the rostrum, head, operculum, and throat are epithelial invaginations which are not connected to lateral line canals. No nerves lead to the pits. The spherical to cuboidal and often ciliated cells at the base of the pits are considered to be aplasic cells of unformed neuromasts.     

Contemporary status of the North American paddlefish, Polyodon spathula

North American paddlefish, Polyodon spathula, were once abundant in most large rivers and tributaries of the Mississippi River basin, but numbers have declined dramatically in most areas during the past 100 years. Habitat destruction and river modification are the most obvious changes affecting their distribution and abundance. Although peripheral range has dwindled, paddlefish still occur over most of their historic range and are still found in 22 states. Populations are currently increasing in 3 states, stable in 14, declining in 2, unknown in 3, and extirpated in 4. Sport harvests presently occur in 14 states, however two states with traditionally important sport fisheries report decreased recruitment into the population and are planning more restrictive regulations. Commercial fisheries are reported in only six states. During the past 10 years, five states have removed paddlefish from their commercial list primarily because of declines in adult stocks due to overfishing or illegal fishing. Ten states are currently stocking paddlefish to supplement existing populations or to recover paddlefish populations in the periphery of its native range.     

Ultrastructural study of spermatozoa of the paddlefish, Polyodon spathula

Paddlefish, Polyodon spathula, spermatozoa were examined by transmission electron microscopy. Their structure has the same characteristic architectural features as sturgeon spermatozoa. Paddlefish spermatozoa are of the primitive type and consist of a rod-shaped head, a midpiece and a long flagellum. The head is about 5.15 mm in length and contains the nucleus and an apical acrosomal complex. Inside the nucleus there are three nuclear channels that begin in the subacrosomal area and have a triple helical arrangement. An nuclear fossa is present centrally, at the posterior end of the nucleus. The midpiece contains a pair of centrioles in a perpendicular arrangement, mitochondria and a narrow cytoplasmic sleeve. The flagellum has a central axoneme with a 9 + 2 pattern and two lateral projections or fins.     

Development of the paired fins in the paddlefish, Polyodon spathula

In Polyodon spathula, the pectoral fin radials, with the exception of the metapterygium, are derived from the decomposition of a single continuous cartilage fin plate that is continuous with the scapulocoracoid. This cartilage sheet develops two interior splits to form three precursor pieces, and these decompose in a predictable way to generate the propterygium and radials. The metapterygium is an extension of the scapulocoracoid that segments off of it during early development. To our knowledge, this has not been reported for acipenserids or other basal actinopterygians. In teleosts, the proximal radials also develop from the "break up" of an initially continuous paddle-like sheet of cartilage along the posterior edge of the scapulocoracoid, and in Polypterus and sharks a similar pattern holds. Thus, the pattern observed in Polyodon may represent the basal developmental condition for the gnathostome pectoral fin. The process underlying development of the superficially similar cartilages of the pelvic and pectoral fins is different. In the pectoral fin, the metapterygium is segmented off of the scapulocoracoid and other radials form from the decomposition of the cartilage plate. In contrast, individual rod-like basipterygial elements form in a close one-to-one correspondence with the middle radials of the pelvic fin, but later fuse to form an anterior element that is branched in appearance. To evaluate further claims of similarity among the pectoral and pelvic fin elements of various fishes, the course of the development of these structures must be observed. The pectoral fin and girdle in Polyodon ossifies in a different sequence than that proposed as ancestral (and highly conserved) for actinopterygians: the supracleithrum ossifies significantly before the cleithrum. The later ossification of the cleithrum in Polyodon may be related to the primary use of the caudal fin vs. the pectoral fins in their locomotion.     

The histology of the excretory kidney of the paddlefish, Polyodon spathula

Kidney tissue from the freshwater chondrostean fish, Polyodon spathula , was examined by light microscopy. P. spathula has a glomerular excretory kidney. The tubule leading from the glomerulus, based on a variety of stain reactions, is composed of two major cell types. Also based on stain reactions, it appears that ion reabsorption, hence conservation, occurs in distal portions of the tubules. Also observed were stain reactions of arteriole walls, similar to renin producing cells in other vertebrates.     

Photoreceptor topography in the duplex retina of the paddlefish (Polyodon spathula)

Retinal whole-mount preparations from the eyes of the North American paddlefish, Polyodon spathula, were examined with a combination of bright field and differential interference contrast microscopy. The entire retina was mapped and population counts of rod and cone photoreceptors were made at regular intervals throughout the retina. The retina is dominated by rods, but a significant percentage (ca. 38%) of the photoreceptors are cones. Mean cone packing density for the entire retina is 6,402+/-1,216 cones/mm2. There is a small (16%) but statistically significant difference between cone packing density in the dorsal retina (6,674+/-1,168 cones/mm2) and the ventral retina (5,745+/-1,076 cones/mm2). There is no region of unusually high cone concentration that might be construed as a fovea or a visual streak. Mean rod packing density for the entire retina is 10,271+/-1,205 rods/mm2. Except in the far periphery, where rods are less numerous, the density of rods is fairly uniform throughout the retina. The data are discussed with regard to paddlefish habitat and behavior.     

Anatomy and histology of the digestive system of the paddlefish (Polyodon spathula)

The paddlefish (Polyodon spathula) is one of the most primitive and unique freshwater fishes of North America. It is adapted as a plankton filter-feeder. The wide mouth and greatly expansible pharyngeal cavity allows it to process a large quantity of water. Numerous setiform gillrakers, which operate against the flattened surfaces of the gill arches and opercula, are capable of filtering out small food particles. The abundance of taste buds and mucus secreting cells in the buccal cavity and pharynx probably aids in selecting and entangling the food. The first segment of the stomach is provided with peculiar, large longitudinal rods of fat which may help in selecting food from water by causing occlusion of the small lumen when the striated fibers of the muscularis contract. Teeth, unnecessary for microphagous fishes, are absent in adults. The digestive tube is one of the most complex present in fishes. It has two distinct divisions of the stomach and four distinct divisions of the intestine besides possessing a large caecum. Ciliated epithelial cells occur in many parts of the gut and may be an aid in moving or processing the small items of food. Besides the presence of cilia, other primitive features of the digestive tract include the lack of distinction between the esophagus and stomach, the presence of a spiral valve, and the presence of some of the diffuse pancreatic tissue within the wall of the gut. The numerous Peyer's patches in the wall of much of the intestine may be an immunological response to the heavy parasitic infestation.     

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.     

匙吻鲟仔稚鱼开口规格及摄食选择的实验研究

我国匙吻鲟(Polyodon spathula)仔稚鱼培育历史将近20年,目前成活率总体上还不高且有很大的波动性[1-5],与原产地美国本土相比有一定的差距,影响了我国匙吻鲟养殖业的发展.仔稚鱼培育是匙吻鲟养殖过程中非常重要的环节,Tania,et al.     

Two modes of information processing in the electrosensory system of the paddlefish (Polyodon spathula)

Paddlefish are uniquely adapted for the detection of their prey, small water fleas, by primarily using their passive electrosensory system. In a recent anatomical study, we found two populations of secondary neurons in the electrosensory hind brain area (dorsal octavolateral nucleus, DON). Cells in the anterior DON project to the contralateral tectum, whereas cells in the posterior DON project bilaterally to the torus semicircularis and lateral mesencephalic nucleus. In this study, we investigated the properties of both populations and found that they form two physiologically different populations. Cells in the posterior DON are about one order of magnitude more sensitive and respond better to stimuli with lower frequency content than anterior cells. The posterior cells are, therefore, better suited to detect distant prey represented by low-amplitude signals at the receptors, along with a lower frequency spectrum, whereas cells in the anterior DON may only be able to sense nearby prey. This suggests the existence of two distinct channels for electrosensory information processing: one for proximal signals via the anterior DON and one for distant stimuli via the posterior DON with the sensory input fed into the appropriate ascending channels based on the relative sensitivity of both cell populations.     

New genus and species of Aporocotylidae (Digenea) from a basal actinopterygian, the American paddlefish, Polyodon spathula, (Acipenseriformes: Polyodontidae) from the Mississippi Delta

Acipensericola petersoni n. gen., n. sp. (Digenea: Aporocotylidae) infects the heart of the American paddlefish Polyodon spathula (Walbaum, 1792) in the Mississippi Delta. It has robust, spike-like body spines arranged in ventrolateral transverse rows; a bowl-shaped anterior sucker centered on the mouth and having minute spines on the inner anteroventral surface only; a pharynx; an inverse U-shaped ceca extending to near the posterior body end; intercecal testes comprising a pre-ovarian testicular column plus a single testis posteriorly; an extensively lobed ovary located medially and immediately posterior to the testicular column; a spherical ootype that is intercecal and post-ovarian; a Laurer's canal; and a common genital pore. The new species is the first-named aporocotylid collected from a basal actinopterygian. It resembles the chondrichthyan aporocotylids Chimaerohemecus trondheimensis, Orchispirium heterovitellatum, and Hyperandrotrema cetorhini in having an inverse U-shaped ceca, but it is morphologically most similar to the anguilliform aporocotylid Paracardicoloides yamagutii in having that feature plus a comparable anterior sucker, a single testis posteriorly, an intertesticular ovary, and a common genital pore. Sequence data for the complete small subunit ribosomal DNA (18S) do not refute its membership within Aporocotylidae nor its affinity to 1 of those aforementioned aporocotylids: A. petersoni was basal to the few teleost aporocotylids analyzed, and C. trondheimensis was the only taxon basal to A. petersoni. We regard the specimens of Spirorchis sp. previously reported from the shortnose sturgeon Acipenser brevirostrum Lesueur, 1818 as congeneric with the new species.