View source for American paddlefish

{{Short description|Species of freshwater fish}}
{{Use mdy dates|date=December 2020}}
{{Featured article}}
{{Speciesbox
| fossil_range = {{Fossil range|Early Paleocene|Present}}
| image = Paddlefish-USFWS-Fish-and-Aquatic-Conservation-2160x1440.jpg
| image_caption = American paddlefish
| status = VU
| status_system = IUCN3.1
| status_ref = <ref name="IUCN">{{cite iucn |author=Moore, M. |author2=Rider, S. |year=2022 |title=''Polyodon spathula'' |article-number=e.T17938A81763841 |doi=10.2305/IUCN.UK.2022-1.RLTS.T17938A81763841.en}}</ref>
| status2 = CITES_A2
| status2_system = CITES
| status2_ref = <ref>{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}</ref>
| genus = Polyodon
| species = spathula
| authority = ([[Johann Julius Walbaum|Walbaum]], 1792)<ref name ="Walbaum">{{cite book |last1=Walbaum |first1=J.J. |title=Petri ArPetri Artedi sueci genera Piscium in quibus systema totum ichthyologiae proponitur cum classibus, ordinibus, generum characteribus, specierum diffentiis, observationibus plumiris. Redactis Speciebus 2. Ichthyologiae, III |date=1792 |publisher=Ant. Ferdin. Rose |location=Grypeswaldiae [Greifswald] |page=522 |url=https://www.biodiversitylibrary.org/page/39001739}}</ref>
| range_map = American paddlefish range.jpg
| synonyms_ref = <ref>{{Cite web|last1=Froese|first1=R.|last2=Pauly|first2=D.|year=2017|title=Polydontidae|url=http://www.fishbase.se/Summary/FamilySummary.php?ID=33|website=[[FishBase]] version (02/2017)|access-date=May 18, 2017|url-status=live|archive-url=https://web.archive.org/web/20170824024508/http://www.fishbase.se/Summary/FamilySummary.php?ID=33|archive-date=August 24, 2017}}</ref><ref>{{Cite web|url=http://deeplyfish.com/wp-content/uploads/2017/05/Family-Polyodontidae-PDF.pdf|title=Polydontidae|website=Deeplyfish- fishes of the world|access-date=May 18, 2017|url-status=live|archive-url=https://web.archive.org/web/20170824024507/http://deeplyfish.com/wp-content/uploads/2017/05/Family-Polyodontidae-PDF.pdf|archive-date=August 24, 2017}}</ref>
| range_map_caption = A range map of American paddlefish overlaid with a map of major rivers in the Mississippi basin
| synonyms = {{collapsible list|bullets = true|title=<small>Genus</small>
| ''Spatularia'' <small>Shaw 1804 non Haworth 1821 non van Deventer 1904 non Mehely 1935</small>
| ''Platirostra'' <small>LeSueur 1818</small>
| ''Megarhinus'' <small>Rafinesque 1820 non Schoenherr 1833 nomen nudum non Robineau-Desvoidy 1827</small>
| ''Proceros'' <small>Rafinesque 1820 non Quatrefages 1845</small>
}}
{{collapsible list|bullets = true|title=<small>Species</small>
| ''Squalus spathulus'' <small>Walbaum 1792</small>
| ''Megarhinus paradoxus'' <small>Rafinesque 1820</small>
| ''Platirostra edentula'' <small>Lesueur 1818</small>
| ''Polyodon feuille'' <small>Lacépède 1797</small>
| ''Polyodon folius'' <small>Bloch & Schneider 1801</small>
| ''Proceros maculatus'' <small>Rafinesque 1820</small>
| ''Spatularia reticulata'' <small>Shaw 1804</small>
| ''Proceros vittatus'' <small>Rafinesque 1820</small>
| ''Accipenser lagenarius'' <small>(sic) Rafinesque 1820</small>
| ?''Polyodon pristis'' <small>Rafinesque 1818</small>
}}
}}

The '''American paddlefish''' ('''''Polyodon spathula'''''), also known as a '''Mississippi paddlefish''', '''spoon-billed cat''', or '''spoonbill''', is a species of [[ray-finned fish]]. It is the last [[extant taxon|living species]] of [[paddlefish]] (Polyodontidae). This family is most closely related to the [[sturgeon]]s; together they make up the [[order (biology)|order]] [[Acipenseriformes]], which are one of the most [[Basal (phylogenetics)|primitive]] living groups of ray-finned fish. Fossil records of other paddlefish species date back 125 million years to the [[Early Cretaceous]], with records of ''Polyodon'' extending back 65 million years to the early [[Paleocene]]. The American paddlefish is a smooth-skinned [[freshwater fish]] with an almost entirely [[cartilage|cartilaginous]] skeleton and a paddle-shaped [[rostrum (anatomy)|rostrum]] (snout), which extends nearly one-third its body length. It has been referred to as a freshwater [[shark]] because of its [[heterocercal]] tail or [[caudal fin]] resembling that of sharks, though it is not closely related.<ref name="Scientific American 2014">{{cite web | title=Extinct freshwater sharks that spawned in saltwater had been mistaken for separate species | website=Scientific American | date=January 16, 2014 | url=https://www.scientificamerican.com/gallery/extinct-freshwater-sharks-that-spawned-in-saltwater-had-been-mistaken-for-separate-species/ | access-date=May 5, 2019}}</ref> The American paddlefish is a highly [[synapomorphy|derived]] fish because it has evolved specialised adaptations, such as [[filter feeder|filter feeding]]. Its rostrum and cranium are covered with tens of thousands of sensory receptors for locating swarms of [[zooplankton]], its primary food source. The only other species of paddlefish that survived to modern times was the [[Chinese paddlefish]] (''Psephurus gladius''), last sighted in 2003 in the [[Yangtze River]] in China and considered to have gone extinct no later than 2010.

The American paddlefish is native to the [[Mississippi River#Watershed|Mississippi River basin]] and once moved freely under the relatively unaltered conditions that existed prior to the early 1900s. It commonly inhabited large, free-flowing rivers, [[braided river|braided channels]], backwaters, and [[oxbow lake]]s throughout the Mississippi River drainage basin, and adjacent [[Gulf Coast of the United States|Gulf Coast]] drainages. Its peripheral range extended into the [[Great Lakes]], with occurrences in [[Lake Huron]] and Lake Helen in Canada until about 1917.<ref>{{cite web|url=https://www.sararegistry.gc.ca/virtual_sara/files/cosewic/sr_paddlefish_0808_e.pdf
|title=COSEWIC assessment and update status report on the paddlefish Polyodon spathula in Canada
|publisher=Committee on the Status of Endangered Wildlife in Canada
|date=April 2008
}}</ref><ref>{{cite web|url=http://www.dfo-mpo.gc.ca/species-especes/species-especes/paddlefish-spatulaire-eng.htm |publisher=Fisheries and Oceans Canada |title=Aquatic Species at Rick&nbsp;– The Paddlefish |date=June 28, 2010 |access-date=December 10, 2014 |archive-url=https://web.archive.org/web/20140807085933/http://www.dfo-mpo.gc.ca/species-especes/species-especes/paddlefish-spatulaire-eng.htm |archive-date=August 7, 2014 }}</ref> American paddlefish populations have declined dramatically primarily because of [[overfishing]], [[habitat destruction]], and [[water pollution|pollution]]. [[Poaching]] has also been a contributing factor to its decline and is liable to continue to be so as long as the demand for [[caviar]] remains strong. Naturally occurring American paddlefish populations have been [[local extinction|extirpated]] from most of their peripheral range, as well as from [[New York (state)|New York]], [[Maryland]], [[Virginia]], and [[Pennsylvania]]. They have been [[species reintroduction|reintroduced]] in the [[Allegheny River|Allegheny]], [[Monongahela River|Monongahela]] and [[Ohio River|Ohio]] river systems in western Pennsylvania. However, their current range has been reduced to the Mississippi and [[Missouri River]] tributaries and [[Mobile Bay]] drainage basin. American paddlefish are currently found in twenty-two states in the U.S., and are protected under state, federal and international laws.

==Taxonomy, etymology and evolution==
[[File:Paddlefish underwater.jpeg|thumb|260px|An American paddlefish in a large aquarium tank]]

In 1797, French naturalist [[Bernard Germain de Lacépède]] established the genus ''Polyodon'' for paddlefish,<ref name ="Lacepede">{{cite journal |last1=Lacépède |first1=B.G.E. |title=Mémoire sur le polyodon feuille |journal=Bulletin des Sciences, par la Société Philomathique de Paris |date=1797 |volume=1 |issue=6 |page=49 |url=https://www.biodiversitylibrary.org/page/5492440}}</ref> which today includes a single extant species, ''Polyodon spathula''. Lacépède disagreed with [[Pierre Joseph Bonnaterre]]'s description in {{lang|fr|[[Tableau encyclopédique et méthodique]]}} (1788), which had suggested that paddlefish were a species of shark. When Lacépède established his [[binomial nomenclature|binomial name]] ''Polydon feuille'' he was unaware the species had already been described in 1792 by taxonomist [[Johann Julius Walbaum]], who had named it as ''Squalus spathula''.<ref name ="Walbaum"/><ref name="JStorHist">{{cite journal | jstor=1445053 | title=History of a Neglected Account of the Paddlefish, ''Polyodon spathula'' | author=Daniel McKinley | journal=Copeia | volume=1984 | issue=1 | pages=201–204| date=February 1984| doi=10.2307/1445053}}</ref><ref name="AFS">{{cite book|chapter-url=http://www.paddlefishfarming.com/files/UpdatesAug2013/Mims_2005_Aquaculture_in_the_21_century-paddlefish.pdf |contribution=Paddlefish |publisher=American Fisheries Society |editor1=Anita Kelly |editor2=Jeff Silverstein |author1=Steven Mims |author2=William L. Shelton |title=Aquaculture in the 21st Century |isbn=978-1-888569-71-1 |issue=46 |pages=227–249 |date=January 2005 |access-date=November 9, 2014 |archive-url=https://web.archive.org/web/20150924063138/http://www.paddlefishfarming.com/files/UpdatesAug2013/Mims_2005_Aquaculture_in_the_21_century-paddlefish.pdf |archive-date=September 24, 2015 }}</ref> Consequently ''spathula'' has priority as the specific name (and 'Walbaum, 1792' is the taxonomic authority to be cited).<ref name=EOL>{{cite book|url=http://eol.org/pages/208600/names/synonyms|publisher=Encyclopedia of Life|title=Polyodon spathula|date=2013|access-date=October 15, 2014|url-status=live|archive-url=https://web.archive.org/web/20151208211312/http://www.eol.org/pages/208600/names/synonyms|archive-date=December 8, 2015}}</ref> But Walbaum's generic name ''[[Squalus]]'' was already in use for [[Squalidae|dogfish]], so Lacépède's ''Polyodon'' is the valid name for this paddlefish genus. Hence '''Polyodon spathula'' (Walbaum, 1792)' is the accepted full scientific name of the American paddlefish.<ref>{{cite book |last1=Fricke |first1=R. |last2=Eschmeyer |first2=W.N. |last3=Van der Laan |first3=R. |title=Eschmeyer's catalog of fishes: genera, species, references: electronic version |date=2022 |publisher=California Academy of Sciences |url=http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp |access-date=24 April 2022}}</ref>

The American paddlefish is the sole surviving species in the paddlefish family, the [[Polyodontidae]]. This is the [[sister group]] to the [[sturgeons]] (family Acipenseridae); evidence from DNA sequences suggest that their [[Most recent common ancestor|last common ancestor]] lived roughly 140 million years ago.<ref name="Peng2007">{{cite journal |last1=Peng |first1=Z. |last2=Ludwig |first2=A. |last3=Wang |first3=D. |last4=Diogo |first4=R. |last5=Wei |first5=Q. |last6=He |first6=S. |title=Age and biogeography of major clades in sturgeons and paddlefishes (Pisces: Acipenseriformes) |journal=Molecular Phylogenetics and Evolution |date=March 2007 |volume=42 |issue=3 |pages=854–862 |doi=10.1016/j.ympev.2006.09.008|pmid=17158071 |bibcode=2007MolPE..42..854P }}</ref> Together these families compose the [[Acipenseriformes]], an order of [[basal (phylogenetics)|basal]] [[ray-finned fish]]es.<ref name="RSPB">{{cite journal |title=A New Time-Scale for Ray-Finned Fish Evolution |author=Imogen A. Hurley |author2=Rachel Lockridge Mueller |author3=Katherine A. Dunn |author4=Eric J. Schmidt |author5=Matt Friedman |author6=Robert K. Ho |author7=Victoria E. Prince |author8=Ziheng Yang |author9=Mark G. Thomas |author10=Michael I. Coates |journal=  Proceedings of the Royal Society B: Biological Sciences|date=February 2007 |volume=274 |issue=1609 |pages=489–498 |doi=10.1098/rspb.2006.3749 |pmid=17476768 |pmc=1766393 }}</ref> Paddlefish have a long fossil record dating back to the [[Early Cretaceous]] 125 million years ago.<ref name="Murray2020"/> American paddlefish are often referred to as [[primitive fish]], or [[relict species]], because of morphological characteristics that they retain from some of their early fossil ancestors.<ref name="INHS">{{cite web | url=http://wwx.inhs.illinois.edu/resources/inhsreports/spring-02/padfish/ | title=Species Spotlight: Paddlefish | publisher=University of Illinois at Urbana-Champaign | work=Illinois Natural History Survey | access-date=June 18, 2014 | author=Susan Post | url-status=live | archive-url=https://web.archive.org/web/20140529051611/http://wwx.inhs.illinois.edu/resources/inhsreports/spring-02/padfish/ | archive-date=May 29, 2014 }}</ref> These characteristics include a skeleton composed primarily of [[cartilage]], and a deeply forked [[heterocercal]] (spine extending into the upper lobe) [[caudal fin]] similar to that of [[shark]]s, although they are not closely related.<ref name=UMESC>{{cite web | url=http://www.umesc.usgs.gov/aquatic/fish/paddlefish/faq.html | publisher=Upper Midwest Environmental Sciences Center, US Geological Survey | title=Paddlefish Study Project | date=March 13, 2014 | author=Steven Zigler | access-date=October 15, 2014 | archive-url=https://web.archive.org/web/20141006120107/http://www.umesc.usgs.gov/aquatic/fish/paddlefish/faq.html | archive-date=October 6, 2014 }}</ref>

The family Polyodontidae comprises six known species: three fossil species from western North America, one fossil species from China,<ref name="Murray2020">{{cite journal |last1=Murray |first1=Alison M. |last2=Brinkman |first2=Donald B. |last3=DeMar |first3=David G. |last4=Wilson |first4=Gregory P. |title=Paddlefish and sturgeon (Chondrostei: Acipenseriformes: Polyodontidae and Acipenseridae) from lower Paleocene deposits of Montana, U.S.A. |journal=Journal of Vertebrate Paleontology |date=3 March 2020 |volume=40 |issue=2 |article-number=e1775091 |doi=10.1080/02724634.2020.1775091|bibcode=2020JVPal..40E5091M |s2cid=222213273 }}</ref> one recently extinct species from China (the [[Chinese paddlefish]], ''Psephurus gladius''; last recorded 2003),<ref name="Zhang Jarić Roberts He 2020 p=136242">{{cite journal | last1=Zhang | first1=Hui | last2=Jarić | first2=Ivan | last3=Roberts | first3=David L. | last4=He | first4=Yongfeng | last5=Du | first5=Hao | last6=Wu | first6=Jinming | last7=Wang | first7=Chengyou | last8=Wei | first8=Qiwei | title=Extinction of one of the world's largest freshwater fishes: Lessons for conserving the endangered Yangtze fauna | journal=Science of the Total Environment | publisher=Elsevier BV | volume=710 | year=2020 | issn=0048-9697 | doi=10.1016/j.scitotenv.2019.136242 | article-number=136242| pmid=31911255 | bibcode=2020ScTEn.71036242Z | s2cid=210086307 }}</ref><ref name="Oceanographic 2020">{{cite web | title=Study declares ancient Chinese paddlefish extinct | website=Oceanographic | date=2020-01-09 | url=https://www.oceanographicmagazine.com/news/chinese-paddlefish-extinct/ | access-date=2022-04-23}}</ref> and the single extant species, the American paddlefish, native to the Mississippi River Basin in the United States.<ref name=MnDNR>{{cite web|url=http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=AFCAB01010|publisher=Minnesota Department of Natural Resources|title=''Polyodon spathula'' (Walbaum, 1792)|date=2014|access-date=October 14, 2014|url-status=live|archive-url=https://web.archive.org/web/20141019133739/http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=AFCAB01010|archive-date=October 19, 2014}}</ref> DNA sequences suggest the Chinese and American paddlefishes diverged about 68 million years ago.<ref name ="Peng2007"/> The oldest fossils of paddlefish belonging to ''[[Polyodon]]'' are those of ''[[Polyodon tuberculata|P. tuberculata]]'' from the Lower [[Paleocene]] Tullock Member of the [[Fort Union Formation]] in Montana, dating to around 65 million years ago.<ref name="Murray2020"/><ref name="Warren">{{cite book|author1=M.L. Warren|url=https://books.google.com/books?id=iUrcAwAAQBAJ&q=Freshwater+Fishes+of+North+America%3A+Volume+1%3A+Petromyzontidae+to+Catostomidae|title=Freshwater Fishes of North America: Volume 1: Petromyzontidae to Catostomidae|author2=B.M. Burr|author3=J.R. Tomelleri|publisher=Johns Hopkins University Press|year=2014|isbn=978-1-4214-1202-3|page=211|oclc=883820201}}</ref> An elongated rostrum is a morphological characteristic of Polyodontidae, but only the genus ''Polyodon'' has characteristics adapted specifically for filter feeding, including the jaw, gill arches, and cranium. The gill rakers of American paddlefish are composed of extensive comb-like filaments believed to have inspired the [[etymology]] of the genus name, ''Polyodon'', a Greek compound word meaning "many toothed". Adult American paddlefish are actually toothless, although numerous small teeth less than {{cvt|1|mm|in}} were found in a juvenile paddlefish measuring {{cvt|630|mm|in}}. The name ''spathula'' references the elongated, paddle-shaped snout or rostrum.<ref name="HelfmanCollette2009">{{cite book|author=Gene Helfman|author2=Bruce B. Collette|author3=Douglas E. Facey|author4=Brian W. Bowen|title=The Diversity of Fishes: Biology, Evolution, and Ecology|url=https://books.google.com/books?id=FyehAR6hsUUC&pg=PA254|date=April 3, 2009|publisher=John Wiley & Sons|isbn=978-1-4443-1190-7|page=254|url-status=live|archive-url=https://web.archive.org/web/20160617190622/https://books.google.com/books?id=FyehAR6hsUUC&pg=PA254|archive-date=June 17, 2016}}</ref><ref name="TSU">{{cite web |url=http://txstate.fishesoftexas.org/polydon%20spathula.htm |title=Polyodon spathula |publisher=Texas National History Collection, a division of Texas Natural Science Center, University of Texas at Austin |work=Fishes of Texas Project and Online Database |date=2007 |access-date=June 19, 2014 |author1=Carla Hassan-Williams |author2=Timothy H. Bonner |url-status=live |archive-url=https://web.archive.org/web/20140726121402/http://txstate.fishesoftexas.org/polydon%20spathula.htm |archive-date=July 26, 2014 }}</ref> Compared to Chinese paddlefish and fossil genera, American paddlefish (and the fossil relative ''P. tuberculata'') are considered to be highly [[Derived (phylogenetics)|derived]] because of their specialised adaptations.<ref name="BioScience">{{cite journal | journal=BioScience | title=The paddlefish rostrum as an electrosensory organ: a novel adaptation for plankton feeding | volume=57 | issue=5 | author=Lon A. Wilkens Michael | author2=H. Hofmann | name-list-style=amp | pages=399–407 | date=2007 | doi=10.1641/B570505 | doi-access=free }}</ref>

Unlike the [[planktivorous]] American paddlefish, Chinese paddlefish were strong swimmers, grew larger, and were opportunistic [[piscivore]]s that fed on small fishes and crustaceans. Some distinct morphological differences of Chinese paddlefish include a narrower, sword-like rostrum, and a protrusible mouth. They also had fewer, thicker gill rakers than American paddlefish.<ref name="HelfmanCollette2009"/><ref name="TSU"/>

==Description==
[[File:General Morphology of Paddlefish.png|thumb|260px|General morphology of the American paddlefish]]
[[File:American paddlefish filter feeding.webm|thumb|260px|thumbtime=0:20|Paddlefish ram suspension-feeding zooplankton in aquarium]]

American paddlefish are among the largest and longest-lived freshwater fishes in North America.<ref name="Jennings">{{cite book|chapter-url=http://ww.fisheries.org/proofs/pad/jennings.pdf |contribution=Distribution, Ecology, and Life History; Biology and Life History of Paddlefish in North America: An Update |publisher=American Fisheries Society |editor1=Craig P. Paukert |editor2=George D. Scholten |title=Paddlefish Management, Propagation, and Conservation in the 21st Century |author1=Cecil A. Jennings |author2=Steven J. Zigler |volume=66 |issue=1 |pages=1–22 |date=2009 |isbn=978-1-934874-12-7 |access-date=June 18, 2014 |archive-url=https://web.archive.org/web/20140714165421/http://ww.fisheries.org/proofs/pad/jennings.pdf |archive-date=July 14, 2014 }}</ref> They have a shark-like body, average {{convert|1.5|m|ft|abbr=on}} in length, weigh {{convert|27|kg|lb|abbr=on}}, and can live in excess of thirty years.<ref name="WWF">{{cite web | url=http://wwf.panda.org/what_we_do/endangered_species/paddlefish/ | title=Paddlefish | publisher=World Wildlife Federation | access-date=June 19, 2014 | url-status=live | archive-url=https://web.archive.org/web/20140723073024/http://wwf.panda.org/what_we_do/endangered_species/paddlefish/ | archive-date=July 23, 2014 }}</ref> For most populations the median age is five to eight years and the maximum age is fourteen to eighteen years.<ref name="Jennings" /> The age of American paddlefish is best determined by [[dentary]] studies, a process which usually occurs on fish harvested during [[snagging]] season, a popular sport fishing activity in certain parts of the U.S. The dentary is removed from the lower jawbone, cleaned of any remaining soft tissue, and cross-sectioned to expose the annual rings. The dentary rings are counted in much the same way a tree is aged. Dentary studies suggest that some individuals can live 60 years or longer, and that females typically live longer and grow larger than males.<ref name="AFS-MT">{{cite web | url=http://www.fisheriessociety.org/AFSmontana/Paddlefish.html | publisher=Montana Chapter of the American Fisheries Society | title=Paddlefish | author1=D.L. Scarnechhia | author2=Brad Schmitz | work=Species of Concern | date=2010 | access-date=August 28, 2014 | archive-url=https://web.archive.org/web/20150924013347/http://www.fisheriessociety.org/AFSmontana/Paddlefish.html | archive-date=September 24, 2015 }}</ref>

American paddlefish are smooth-skinned and almost entirely cartilaginous. Their eyes are small and directed laterally. They have a large, tapering [[operculum (fish)|operculum flap]], a large mouth, and a flat, paddle-shaped rostrum that measures approximately one-third of their body length. During the initial stages of development from [[embryo]] to [[hatchling]], American paddlefish have no rostrum. It begins to form shortly after hatching.<ref name="LSU">{{cite web | url=http://www.lamer.lsu.edu/pdfs/NFC_Section1.pdf | publisher=Louisiana State University | title=Biology of the Paddlefish | work=Louisiana Marine Education Resources, Classroom Projects | access-date=June 9, 2014 | archive-url=https://web.archive.org/web/20140714195741/http://www.lamer.lsu.edu/pdfs/NFC_Section1.pdf | archive-date=July 14, 2014 }}</ref><ref name="FWSBrochure">{{cite web|url=http://www.fws.gov/midwest/fisheries/library/broch-paddle.pdf|title=Paddlefish ''Polyodon Spathula''|publisher=U.S. Fish & Wildlife Service|date=May 16, 2001|access-date=June 20, 2014|url-status=live|archive-url=https://web.archive.org/web/20150924045947/http://www.fws.gov/midwest/fisheries/library/broch-paddle.pdf|archive-date=September 24, 2015}}</ref>  The rostrum is an extension of the cranium, not of the upper and lower jaws or [[olfactory receptor|olfactory system]] as with the long snouts of other fish.<ref name="BioScience"/><ref name="Jennings" /> Other distinguishing characteristics include a deeply forked heterocercal caudal fin and dull coloration, often with mottling, ranging from bluish gray to black [[dorsal (anatomy)|dorsally]] grading to a whitish underbelly.<ref name="TSU"/>

==Feeding ecology and physiology==
Scientists began to debate the function of the American paddlefish's rostrum when the species was described in the late 1700s.<ref name="OhioEdu">{{cite journal |author1=Alexander B. Neiman |author2=David F. Russell |author3=Xing Pei |author4=Winfried Wojtenek |author5=Jennifer Twitty |author6=Enrico Simonotto |author7=Barbara A. Wettring |author8=Eva Wagner |author9=Lon A. Wilkens |author10=Frank Moss |year=2000 |title=Stochastic synchronization of electroreceptors in the paddlefish |url=http://www.phy.ohiou.edu/~neiman/synchronization/ |journal=International Journal of Bifurcation and Chaos |publisher=Ohio University |volume=10 |issue=11 |page=2499 |bibcode=2000IJBC...10.2499N |doi=10.1142/S0218127400001717 |archive-url=https://web.archive.org/web/20150924072749/http://www.phy.ohiou.edu/~neiman/synchronization/ |archive-date=September 24, 2015 |access-date=June 20, 2014|url-access=subscription }}</ref> They had once believed it was used to excavate bottom substrate or functioned as a balancing mechanism and navigational aid.<ref name="LSU"/> However, laboratory experiments in 1993 that utilized advanced technology in the field of [[electron microscopy]] have established conclusively that the rostrum of American paddlefish is covered with tens of thousands of sensory receptors. These receptors are morphologically similar to the [[ampullae of Lorenzini]] of sharks and [[ray (fish)|rays]], and are indeed passive [[Electroreception and electrogenesis#Passive electrolocation|ampullary]]-type [[electroreceptor]]s used by American paddlefish to detect [[plankton]].<ref name="OhioEdu" /> Clusters of electroreceptors also cover the head and operculum flaps. The diet of the American paddlefish consists primarily of [[zooplankton]]. Examples of animals in the ''P. spathula'' diet are [[copepod]]s, [[Diplostraca|cladoceran]]s such as ''[[Daphnia pulex]]'', and [[Mayfly|ephemeropteran]] nymphs.<ref>{{cite web | url=https://animaldiversity.org/accounts/Polyodon_spathula/ | title=Polyodon spathula (American paddlefish) | website=[[Animal Diversity Web]] }}</ref> Their electroreceptors can detect weak electrical fields that signal not only the presence of zooplankton, but also the individual feeding and swimming movements of zooplankton appendages.<ref name="LSU" /> When a swarm of zooplankton is detected, the paddlefish swims forward continuously with its mouth wide open, forcing water over the gill rakers to filter out prey. Such feeding behavior is considered ram suspension-feeding.  Further research has indicated that the electroreceptor of the paddlefish may serve as a navigational aid for obstacle avoidance.<ref name="OhioEdu" /><ref name="LSU"/>

American paddlefish have small undeveloped eyes that are directed laterally. Unlike most fishes, American paddlefish hardly respond to overhead shadows or changes in illumination. Electroreception appears to have largely replaced vision as a primary sensory modality, which indicates a reliance on electroreceptors for detecting prey.<ref name="OhioEdu" /><ref name="LSU" /> However, the rostrum is not their only means of food detection. Some reports suggest a damaged rostrum would render American paddlefish less capable of foraging efficiently to maintain good health, but laboratory experiments and field research indicate otherwise.<ref name="BioScience" /><ref name="LSU" /> As well as electroreceptors on the rostrum, American paddlefish have sensory pores covering nearly half of the skin surface extending from the rostrum to the top of the head down to the tips of the operculum flaps. Studies have indicated that American paddlefish with damaged or abbreviated rostrums are still able to forage and maintain good health.<ref name="BioScience" /><ref name="LSU" />

==Reproduction and life cycle==
[[File:Paddlefish transformation from embryo to larval stage of development.webm|thumb|260px|Development of paddlefish from embryo to larval stage]]
[[File:American paddlefish fry at 30 days of age - 2013.jpg|thumb|260px|Stages of rostrum development|right]]

American paddlefish are long-lived, sexually late maturing [[pelagic fish]]. Females do not begin [[spawn (biology)|spawning]] until they are seven to ten years old, some as late as sixteen to eighteen years old. Females do not spawn every year; rather they spawn every second or third year. Males spawn more frequently, usually every year or every other year beginning around age seven, some as late as nine or ten years of age.<ref name="LSU"/><ref name="ND">{{cite web|url=http://gf.nd.gov/fishing/other-fishing-information/paddlefish-snagging-season/paddlefish-questions-and-answers |publisher=North Dakota Game and Fish Department |title=Paddlefish Questions and Answers |date=2012 |access-date=June 9, 2014 |archive-url=https://web.archive.org/web/20150624063851/http://gf.nd.gov/fishing/other-fishing-information/paddlefish-snagging-season/paddlefish-questions-and-answers |archive-date=June 24, 2015 }}</ref>

American paddlefish begin their upstream spawning migration sometime during early spring; some begin in late fall.<ref name="ND"/> They spawn on silt-free gravel bars that would otherwise be exposed to air or covered by very shallow water were it not for the rises in the river from snow melt and annual spring rains that cause flooding.<ref name="MDC">{{cite web |url=https://nature.mdc.mo.gov/discover-nature/field-guide/search/paddlefish |publisher=Missouri Department of Conservation |title=Paddlefish, ''Polyodon spathula'' |work=Discover Nature Field Guide |access-date=June 9, 2014 |url-status=live |archive-url=https://web.archive.org/web/20170824024506/https://nature.mdc.mo.gov/discover-nature/field-guide/search/paddlefish |archive-date=August 24, 2017 }}</ref> Although availability of preferred spawning habitat is essential, there are three precise environmental events that must occur before American paddlefish will spawn.<ref name=EWS>{{cite web|url=http://www.earthwave.org/paddlefish|publisher=Earthwave Society|title=Paddlefish|author=Betty Wills|date=2004|access-date=October 3, 2014|url-status=live|archive-url=https://web.archive.org/web/20141006103219/http://www.earthwave.org/paddlefish|archive-date=October 6, 2014}}</ref><ref name="LSU" /> The water temperature must be from {{convert|55|to|60|F|C}}; the lengthened [[photoperiodism|photoperiod]] which occurs in spring triggers biological and behavioral processes that are dependent on increasing day length; and there must be a proper rise and flow in the river before a successful spawn can occur. Historically, American paddlefish did not spawn every year because the precise environmental events occurred just once every 4 or 5 years.<ref name="EWS" />

American paddlefish are [[broadcast spawner]]s, also referred to as mass spawners or synchronous spawners. [[Gravid]] females release their [[egg (biology)|eggs]] into the water over bare rocks or gravel at the same time males release their [[spermatozoon|sperm]]. Fertilization occurs externally. The eggs become sticky after they are released into the water and will attach to the bottom substrate. Incubation varies depending on water temperature, but in {{convert|60|F|C|abbr=on}} water the eggs will hatch into [[larval fish]] in about seven days.<ref name="ND" /> After hatching, the larval fish drift downstream into areas of low flow velocity where they forage on zooplankton.<ref name="ND"/>

Young American paddlefish are poor swimmers which makes them susceptible to predation. Therefore, rapid first-year growth is important to their survival.<ref name="ND" /> [[Juvenile fish|Fry]] can grow about {{convert|1|inch|cm|abbr=on}} per week,<ref name="PA">{{cite journal|url=https://www.fish.state.pa.us/anglerboater/1999/jf99/padlfish.htm |title=Progress with Paddlefish Restoration |journal=Pennsylvania Angler and Boater |author=Dudley Parr |issue=January/February 1999 |access-date=August 28, 2014 |archive-url=https://web.archive.org/web/20140903095036/https://www.fish.state.pa.us/anglerboater/1999/jf99/padlfish.htm |archive-date=September 3, 2014 }}</ref> and by late July the [[fingerling (fish)|fingerlings]] are around {{convert|5|-|6|in|cm|abbr=on}} long.<ref name="ND"/> Their rate of growth is variable and highly dependent on food abundance. Higher growth rates occur in areas where food is not limited.  The feeding behavior of fingerlings is quite different from that of older juveniles and adults. They capture individual plankton one by one, which requires detection and location of individual ''[[Daphnia]]'' on approach, followed by an intercept maneuver to capture the selected prey.<ref name="OhioEdu" /> By late September fingerlings have developed into juveniles, and are around {{convert|10|-|12|in|cm|abbr=on}} long. After the 1st year their growth rate slows and is highly variable. Studies indicate that by age 5 their growth rate averages around {{convert|2|in|cm|abbr=on}} per year depending on the abundance of food and other environmental influences.<ref name="TSU"/>

==Habitat and distribution==
[[File:Paddlefish distribution.png|thumb|260px|Map of the United States showing distribution of paddlefish]]

American paddlefish are highly mobile and well adapted to living in rivers.<ref name=UMESC/> They inhabit many types of riverine habitats throughout much of the Mississippi Valley and adjacent Gulf slope drainages. They occur most frequently in deeper, low current areas such as side channels, oxbows, backwater lakes, bayous, and tailwaters below dams. They have been observed to move more than {{convert|2000|mi|km|abbr=on}} in a river system.<ref name=UMESC/>

American paddlefish are endemic to the Mississippi River Basin, historically occurring from the [[Missouri River|Missouri]] and [[Yellowstone River|Yellowstone]] rivers in the northwest to the Ohio and Allegheny rivers of the northeast; the headwaters of the Mississippi River south to its mouth, from the [[San Jacinto River (Texas)|San Jacinto River]] in the southwest to the [[Tombigbee River|Tombigbee]] and [[Alabama River|Alabama]] rivers of the southeast.<ref name="Jennings"/> They were extirpated from New York, Maryland and Pennsylvania, as well as from much of their peripheral range in the Great Lakes region, including Lake Huron and Lake Helen in Canada.<ref name=IUCN2/><ref name=EWS/> In 1991, Pennsylvania implemented a [[species reintroduction|reintroduction]] program utilizing [[hatchery]]-reared American paddlefish in an effort to establish self-sustaining populations in the upper Ohio and lower Allegheny rivers. In 1998, New York initiated a stocking program upstream in the [[Allegheny Reservoir]] above Kinzua Dam, and a second stocking in 2006 in [[Conewango Creek]], a relatively unaltered section of their historic range. Reports of free ranging adults captured by gill nets have since been documented in Pennsylvania and New York, but there is no evidence of natural reproduction.<ref name="Status">{{cite book|author1=Phillip W. Bettoli|chapter-url=https://usgs-cru-individual-data.s3.amazonaws.com/pbettoli/intellcont/Status%2520of%2520Paddlefish_May%25202009%2520Proofs-1.pdf|contribution=Status of Paddlefish in the United States|author2=Janice A. Kerns|author3=George D. Scholten|date=December 2009|title=Paddlefish Management, Propagation, and Conservation in the 21st Century|publisher=American Fisheries Society|isbn=978-1-934874-12-7|editor1=Craig P. Paukert|pages=1–16|editor2=George D. Scholten|issue=66|access-date=January 27, 2022|archive-date=April 23, 2022|archive-url=https://web.archive.org/web/20220423100349/https://usgs-cru-individual-data.s3.amazonaws.com/pbettoli/intellcont/Status%20of%20Paddlefish_May%202009%20Proofs-1.pdf}}</ref><ref name="Argent">{{cite book|chapter-url=http://www.secure.fisheries.org/proofs/pad/argent.pdf |publisher=American Fisheries Society |contribution=Paddlefish Restoration to the Upper Ohio and Allegheny River Systems |title=Paddlefish Management, Propagation, and Conservation in the 21st Century |editor1=Craig P. Paukert |editor2=George D. Scholten |author1=David G. Argent |author2=William G. Kimmel |author3=Rick Lorson |author4=Paul McKeown |author5=Doug M. Carlson |author6=Mike Clancy |issue=66 |pages=1–13 |date=December 2009 |access-date=June 20, 2014 |isbn=978-1-934874-12-7 |archive-url=https://web.archive.org/web/20140714122958/http://www.secure.fisheries.org/proofs/pad/argent.pdf |archive-date=July 14, 2014 }}</ref> They are currently found in 22 states in the US, and are protected under state and federal laws. There are 13 states that allow commercial or sport fishing for American paddlefish.<ref name="LSU"/>

==Human interaction==

===Propagation and culture===
[[File:Paddlefish c-section.webm|thumb|260px|Caesarean-section surgery to extract [[roe]], fertilize, and incubate. Blind Pony Hatchery in Missouri, 1995.]]

The artificial propagation of American paddlefish began with the efforts of the [[Missouri Department of Conservation]] during the early 1960s, and focused primarily on maintenance of the sport fishery.<ref name="Propagation">{{cite book|chapter-url=http://www.paddlefishfarming.com/Mims_2009_Propagation_and_Culture_of_Paddlefish.pdf |publisher=American Fisheries Society |title=Paddlefish Management, Propagation, and Conservation in the 21st Century |editor1=Craig P. Paukert |editor2=George D. Scholten |author1=Steven Mims |author2=William L. Shelton |author3=Richard J. Onders |contribution=Propagation and Culture of Paddlefish |issue=66 |pages=357–383 |date=December 2009 |access-date=June 22, 2014 |isbn=978-1-934874-12-7 |archive-url=https://web.archive.org/web/20140714114332/http://www.paddlefishfarming.com/Mims_2009_Propagation_and_Culture_of_Paddlefish.pdf |archive-date=July 14, 2014 }}</ref>  However, it was the growing importance of American paddlefish for their meat and [[roe]] that became the catalyst for further development of culture techniques for aquaculture in the United States.<ref name="Propagation"/> Artificial propagation requires broodstock which, because of the late sexual maturation of American paddlefish, are initially obtained from the wild and brought into a [[hatchery]] environment.<ref name="LMES">{{cite web | url=http://www.lamer.lsu.edu/nativefish/nfc03.htm | publisher=Louisiana State University | title=Native Fish in the Classroom | work=Louisiana Marine Education Resources, Classroom Projects | access-date=June 22, 2014 | archive-url=https://web.archive.org/web/20140903072808/http://www.lamer.lsu.edu/nativefish/nfc03.htm | archive-date=September 3, 2014 }}</ref> The fish are injected with [[LH-RH]] hormone to stimulate spawning. The number of eggs a female may produce depends on the size of the fish and can range anywhere from 70,000 to 300,000 eggs. Unlike most [[teleostei|teleosts]], the [[oviduct]] branches of American paddlefish and sturgeons are not directly attached to the [[ovary|ovaries]]; rather, they open dorsally into the body cavity. To determine the status of progression toward maturation, ova staging is performed. The process begins with a minor procedure that involves a small abdominal incision from which to extract a few sample [[oocyte]]s. The oocytes are boiled in water for a few minutes until the yolk is hardened, and then they are cut in half to expose the nucleus. The exposed nucleus is examined under a microscope to determine stage of maturity.<ref name="Propagation"/>

Once maturation is confirmed, one of three procedures is used to extract the eggs from a female paddlefish. The three procedures are:

# the traditional hand-stripping method, considered to be time-consuming and laborious;
# [[Caesarean section]], a relatively quick surgical method of extracting eggs through a {{convert|4|in|cm|abbr=on}} abdominal incision which, though considered faster than hand stripping, can involve time-consuming suturing and an incision resulting in muscular stress and poor suture retention which lowers survival rate; and;
# MIST (minimally invasive surgical technique), which is the fastest of the three procedures because it requires less handling of the fish and eliminates the need for suturing. A small internal incision is made in the dorsal area of the oviduct, which allows direct stripping of eggs from the body cavity through the [[gonopore]] bypassing the oviductal funnels.<ref name="SRAC">{{cite web |url=http://www2.ca.uky.edu/wkrec/PaddlefishProduction.pdf |publisher=Southern Regional Aquaculture Center |title=Production of Paddlefish |author1=Steven D. Mims |author2=William L. Shelton |author3=Forrest S. Wynne |author4=Richard J. Onders |work=Texas A&M AgriLife Extension Aquaculture, Fisheries, & Pond Management, Publication 437 |pages=1–5 |date=November 1999 |access-date=June 22, 2014 |archive-url=https://web.archive.org/web/20160910115628/http://www2.ca.uky.edu/wkrec/PaddlefishProduction.pdf |archive-date=September 10, 2016 }}</ref><ref name="MIST">{{cite journal | url=http://ksuaqua.homestead.com/files/research/reproduction/Mims_et_al_2004_Effectiveness_of_the_Minimally_Invasive_Surgical_Technique__MIST__for_Removal_of_Ovulated_Eggs_from_Paddlefish.pdf | title=Technical Notes: Effectiveness of the Minimally Invasive Surgical Technique (MIST) for Removal of Ovulated Eggs from First-Time and Second-Time MIST-Spawned Paddlefish | journal=North American Journal of Aquaculture | author1=Steven Mims | author2=William L. Shelton | author3=Richard J. Onders | author4=Boris Gomelsky | volume=66 | pages=70–72 | date=2004 | access-date=June 22, 2014 | doi=10.1577/c02-053 | archive-url=https://web.archive.org/web/20140714201241/http://ksuaqua.homestead.com/files/research/reproduction/Mims_et_al_2004_Effectiveness_of_the_Minimally_Invasive_Surgical_Technique__MIST__for_Removal_of_Ovulated_Eggs_from_Paddlefish.pdf | archive-date=July 14, 2014 }}</ref>

A spermiating male indicates successful production of mature [[spermatozoon|spermatozoa]] which results in the release of large volumes of [[milt]] over the course of three to four days. Milt is collected by inserting a short plastic tube with syringe attached into the urogenital opening of the male and applying light suction with the syringe to draw the milt. The collected milt is diluted in water just prior to adding it to the eggs and the combination is gently stirred for about a minute to achieve fertilization. Fertilized eggs are adhesive and [[demersal]], therefore if incubation is to take place in a flow-through hatching jar, the eggs must be treated to prevent clumping. Incubation usually takes anywhere from five to twelve days.<ref name="Propagation"/>

===Hybridization===
A 2020 paper reported that eggs from three [[Russian sturgeon]]s were crossbred with American paddlefish using sperm from four male paddlefish, resulting in hybrids called [[sturddlefish]], a blend of the two names. The offspring had a survival rate of 62–74% and on average reached {{Convert|1|kg|lb|abbr=on}} after a year of growth. This was the first time such fish from different families were successfully crossbred.<ref>{{Cite journal|last1=Káldy|first1=Jenő|last2=Mozsár|first2=Attila|last3=Fazekas|first3=Gyöngyvér|last4=Farkas|first4=Móni|last5=Fazekas|first5=Dorottya Lilla|last6=Fazekas|first6=Georgina Lea|last7=Goda|first7=Katalin|last8=Gyöngy|first8=Zsuzsanna|last9=Kovács|first9=Balázs|last10=Semmens|first10=Kenneth|last11=Bercsényi|first11=Miklós|date=July 6, 2020|title=Hybridization of Russian Sturgeon (Acipenser gueldenstaedtii, Brandt and Ratzeberg, 1833) and American Paddlefish (Polyodon spathula, Walbaum 1792) and Evaluation of Their Progeny|journal=Genes|language=en|volume=11|issue=7|page=753|doi=10.3390/genes11070753|pmid=32640744|pmc=7397225|doi-access=free}}</ref> Their last common ancestor is estimated to have lived 140 million years ago.<ref name="Peng2007"/>

===Global commercial market===
[[File:Paddlefish caviar.png|thumb|260px|Tin of freshly processed paddlefish caviar|right]]
Advancements in biotechnology have created a global commercial market for the [[polyculture]] of American paddlefish. In 1970, American paddlefish were stocked in several rivers in Europe and Asia.  [[Introduced species|Introduction]] began when five thousand hatched larvae from Missouri hatcheries in the United States were exported to the former [[Soviet Union]] for [[aquaculture|aquacultural]] utilization.<ref name="Doiserbia">{{cite journal | url=http://www.doiserbia.nb.rs/img/doi/0354-4664/2006/0354-4664060327PL.pdf | title=First Record of the North American Paddlefish (''Polyodon spathula'', Walbaum 1792) in the Serbian Part of the Danube River | author=Mirjana Lenhardt | author2=A. Hegediš | author3=B. Mićković | author4=Željka Višnjić Jeftić | author5=Marija Smederevac | author6=I. Jarić | author7=G. Cvijanović | author8=Z. Gačić | journal=Archives of Biological Science, Belgrade | volume=58 | issue=3 | pages=27P, 28P | date=2006 | access-date=June 9, 2014 | doi=10.2298/abs060327pl | url-status=live | archive-url=https://web.archive.org/web/20140714122704/http://www.doiserbia.nb.rs/img/doi/0354-4664/2006/0354-4664060327PL.pdf | archive-date=July 14, 2014 | doi-access=free }}</ref> Reproduction was successful in 1988 and 1989, and resulted in the exportation of juveniles to Romania and Hungary. American paddlefish are now being raised in Ukraine, Germany, Austria, the Czech Republic, and the Plovdiv and Vidin regions in Bulgaria. In May 2006, specimens of different sizes and weights were caught by professional fisherman near Prahovo in the Serbian part of the [[Danube|Danube River]].<ref name="Doiserbia"/>

In 1988, fertilized American paddlefish eggs and larvae from Missouri hatcheries were first introduced into China.<ref name="Doiserbia"/> Since that time, China imports approximately 4.5{{nbsp}}million fertilized eggs and larvae every year from hatcheries in Russia and the United States. Some American paddlefish are polycultured in carp ponds and sold to restaurants while others are cultured for brood stock and [[caviar]] production.  China has also exported American paddlefish to Cuba, where they are farmed for caviar production.<ref name="Mims">{{cite journal|url=http://pdf.gaalliance.org/pdf/GAA-Mims-Feb06.pdf |title=Paddlefish Culture: Development Expanding Beyond U.S., Russia, China |author=Steven D. Mims |journal=Global Aquaculture Advocate |pages=62–63 |date=February 2006 |access-date=June 10, 2014 |archive-url=https://web.archive.org/web/20140714141327/http://pdf.gaalliance.org/pdf/GAA-Mims-Feb06.pdf |archive-date=July 14, 2014 }}</ref>

===Sport fishing===
American paddlefish are a popular [[sport fish]] where their populations are sufficient to allow such activity. Areas where there are no self-sustaining populations rely on state and federal restocking programs to maintain a viable fishery. A 2009 report includes the following states as allowing American paddlefish sport fishing per their respective state and federal regulations: Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Mississippi, Missouri, Montana, Nebraska, North Dakota, Oklahoma, South Dakota and Tennessee.<ref name="Status" /> Since American paddlefish are filter-feeders, they will not take bait or [[fishing lure|lures]], and must be caught by snagging.<ref name="ND"/>

The official state record in Kansas is an American paddlefish snagged in 2004 that weighed {{convert|144|lb|kg|abbr=on}}. In Montana, an American paddlefish was snagged in 1973 weighing {{convert|142.5|lb|kg|abbr=on}}. In North Dakota, one snagged in 2024 weighed {{convert|131|lb|kg|abbr=on}}.<ref>{{Cite web |last=Anhalt |first=Michael |date=2024-06-04 |title=Mandan angler snags record-breaking paddlefish |url=https://www.kfyrtv.com/2024/06/04/mandan-angler-snags-record-breaking-paddlefish/ |access-date=2024-06-05 |website=www.kfyrtv.com |language=en}}</ref> The largest American paddlefish on record was captured in [[West Okoboji Lake]], Iowa, in 1916 by a spear fisherman; it measured {{convert|85|in|m|abbr=on}} and weighed an estimated {{convert|198|lb|kg|abbr=on}}.<ref name="ND"/><ref>{{cite web |url=http://siouxcityjournal.com/sports/recreation/outdoors/seeking-paddlefish-on-the-missouri/article_4f6f500e-867d-5eb3-86c6-eb877b937265.html |publisher=Sioux City Journal |title=Seeking paddlefish on the Missouri: Outdoors |date=October 11, 2012 |access-date=December 12, 2014 |url-status=live |archive-url=https://web.archive.org/web/20170824024506/http://siouxcityjournal.com/sports/recreation/outdoors/seeking-paddlefish-on-the-missouri/article_4f6f500e-867d-5eb3-86c6-eb877b937265.html |archive-date=August 24, 2017 }}</ref>

==Population declines==
[[File:Angler has paddlefish by rostrum.png|thumbnail|260px|Angler landing a large paddlefish]]

===Overfishing and habitat destruction===
American paddlefish populations have declined dramatically, primarily as a result of overfishing and habitat destruction. In 2004 they were listed as Vulnerable (VU&nbsp;A3de ver&nbsp;3.1) on the [[IUCN Red List of Threatened Species]]. In 2022 the status category was changed to VU&nbsp;A2cd throughout their range as the result of a [[United States Fish and Wildlife Service|U.S. Fish & Wildlife Service]] assessment. The assessment concluded that "an overall population size reduction of at least 30% may occur within the next 10 years or three generations due to actual or potential levels of exploitation and the effects of introduced taxa, pollutants, competitors or parasites."<ref name="IUCN"/> American paddlefish are filter-feeding pelagic fish that require large, free-flowing rivers with braided channels, backwater areas, oxbow lakes that are rich in zooplankton, and gravel bars for spawning.<ref name="MDC" /> Series of dams on rivers such as those constructed on the [[Missouri River]] have impounded large populations of American paddlefish, and blocked their upstream migration to spawning shoals.<ref name="MDC" /> [[River engineering#Channelization|Channelization]] and [[groyne]]s or wing dykes have caused the narrowing of rivers and altered flow, destroying crucial spawning and nursery habitat.<ref name="EWS" /><ref name="Jennings"/><ref name="Status" /> As a result, most impounded populations are not self-sustaining and must be stocked to maintain a viable sport fishery.<ref name="MDC" />

===Zebra mussels===
[[Zebra mussel]] infestations in the Mississippi River, Great Lakes and other Midwest rivers are also negatively affecting American paddlefish populations. Zebra mussels are an [[invasive species]] well adapted for explosive population growth as a result of high rates of [[fecundity]] and recruitment. As filter feeders, zebra mussels rely on plankton and can filter significant amounts of [[phytoplankton]] and zooplankton from the water, altering the availability of an important food source for paddlefish and native [[unionidae]].<ref name="EWS"/><ref name="ZM">{{cite web | url=http://home.nps.gov/mnrr/planyourvisit/upload/Zebra-mussel.pdf | publisher=National Park Service | title=Don't Move a Mussel | author=National Park Service | work=Missouri National Recreational River Zebra Mussel Bulletin | access-date=June 21, 2014 | archive-url=https://web.archive.org/web/20140714130155/http://home.nps.gov/mnrr/planyourvisit/upload/Zebra-mussel.pdf | archive-date=July 14, 2014 }}</ref> A few days after the fertilization of zebra mussel eggs, a microscopic larva emerges called a [[veliger]]. During this initial stage of development, which usually lasts a few weeks, veligers are able to swim freely in the water column with other microscopic animals comprising zooplankton. Veligers are poor swimmers, making them susceptible to predation by any animal that feeds on zooplankton.<ref name=Biokids>{{cite web | url = http://www.biokids.umich.edu/critters/Dreissena_polymorpha/ | publisher = University of Michigan | title = Dreissena polymorpha | author = Tiffany Murphy | work = Animal Diversity Web | date = 2008 | access-date = October 20, 2014 | archive-url = https://web.archive.org/web/20141030152522/http://www.biokids.umich.edu/critters/Dreissena_polymorpha/ | archive-date = October 30, 2014 }}</ref> However, natural predation of zebra mussels at any stage of development has not made a significant contribution to the long-term reduction of zebra mussel populations.<ref name=TandF>{{cite journal | title=Natural Enemies of Zebra Mussels&nbsp;– Predators, Parasites, and Ecological Competitors | author=Daniel P. Molloy | author2=Alexander Y. Karatayev | author3=Lyubov E. Burlakova | author4=Dina P. Kurandina | author5=Franck Laruelle | journal=Reviews in Fisheries Science | volume=5 | issue=1 | pages=83–84 | date=1997 | doi=10.1080/10641269709388593 | bibcode=1997RvFS....5...27M }}</ref>

===Poaching and overexploitation===
[[Poaching]] has been a contributing factor to declining populations of American paddlefish in the states where they are commercially exploited, particularly while the demand for [[caviar]] remains strong.<ref name="Status" />  Since the 1980s, a trade [[embargo]] on [[Iran]] restricted imports of the highly sought after and most expensive [[beluga caviar]] from the [[Caspian Sea]], limiting U.S. sources of caviar. The most sought-after caviar is produced by sturgeons in the Northern Caspian Sea, but overfishing and poaching have exhausted the supply. American sturgeon and paddlefish populations were targeted as likely substitutes.<ref name="LSU" /><ref>{{cite journal |url=https://www.eater.com/2016/3/30/11250870/american-paddlefish-caviar |title=Why the Caviar-Producing American Paddlefish Is a Symbol of Luxury and Scarcity| author=Katherine Cooper| journal=Eater|date=March 30, 2016| access-date=March 8, 2021}}</ref>

The [[fish roe|roe]] of American paddlefish can be processed into caviar similar in taste, color, size and texture to [[sevruga]] sturgeon caviar from the Caspian Sea.<ref name=EWS /><ref name="SRAC"/> Several cases of mislabeled American paddlefish roe sold as Caspian Sea caviar have been prosecuted by the U.S. Fish and Wildlife Service.<ref name="LSU"/> State and federal regulations restricting the harvest of American paddlefish populations in the wild, and the illegal trafficking of their roe, are strictly enforced. Related violations such as the illegal transport of American paddlefish roe have resulted in convictions with substantial fines and prison sentences.<ref name="FWSIndict">{{cite web | url=http://www.fws.gov/news/ShowNews.cfm?ID=07401D8C-0A8F-B153-D150CDEC1E8F306B | publisher=U.S. Fish & Wildlife Service | title=Seven Men Indicted for Alleged Trafficking of Paddlefish Caviar | author=Gavin Shire | date=April 15, 2013 | access-date=June 20, 2014 | url-status=live | archive-url=https://web.archive.org/web/20140821175511/http://www.fws.gov/news/ShowNews.cfm?ID=07401D8C-0A8F-B153-D150CDEC1E8F306B | archive-date=August 21, 2014 }}</ref><ref name="Tulsa">{{cite journal | url=http://www.tulsaworld.com/news/courts/man-gets-prison-term-in-paddlefish-caviar-criminal-case/article_6924b3e0-3866-11e3-be81-0019bb30f31a.html | title=Man Gets Prison Term in Paddlefish 'Caviar' Criminal Case | author=David Harper | journal=Tulsa World | date=October 18, 2013 | access-date=June 20, 2014 | url-status=live | archive-url=https://web.archive.org/web/20150917141847/http://www.chattanoogan.com/2009/7/9/154539/Federal-Authorities-Step-in-to-Protect.aspx | archive-date=September 17, 2015 }}</ref>  American paddlefish are also protected under Appendix II of the [[Convention on International Trade in Endangered Species]] (CITES) meaning international trade in the species (including parts and derivatives) is regulated.<ref name="Chattanoogan">{{cite journal | url=http://www.chattanoogan.com/2009/7/9/154539/Federal-Authorities-Step-in-to-Protect.aspx | journal=The Chattanoogan | title=Federal Authorities Step in to Protect Paddlefish | author=Richard Simms | date=July 9, 2009 | access-date=June 19, 2014 | url-status=live | archive-url=https://web.archive.org/web/20150917141847/http://www.chattanoogan.com/2009/7/9/154539/Federal-Authorities-Step-in-to-Protect.aspx | archive-date=September 17, 2015 }}</ref>

===Extinction of Chinese paddlefish===
The primary reasons for the decline of the now-extinct Chinese paddlefish are similar to those of American paddlefish, which include overfishing, the construction of dams, and destruction of habitat.<ref name=IUCN2>{{cite iucn |author=Qiwei, W. |date=2010 |title=''Psephurus gladius'' |volume=2010 |article-number=e.T18428A8264989 |doi=10.2305/IUCN.UK.2010-1.RLTS.T18428A8264989.en |access-date=13 November 2021}}</ref> The last confirmed sighting of a live Chinese paddlefish was from the [[Yangtze|Yangtze River]] on January 24, 2003.<ref name=BBC>{{cite web|url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8269000/8269414.stm|publisher=BBC Earth News|title=Giant Fish 'Verges on Extinction'|author=Jody Bourton|date=September 29, 2009|access-date=October 6, 2014|url-status=live|archive-url=https://web.archive.org/web/20141006072635/http://news.bbc.co.uk/earth/hi/earth_news/newsid_8269000/8269414.stm|archive-date=October 6, 2014}}</ref> From 2006 to 2008, scientists conducted surveys in an effort to locate the fish. They used several boats, deployed 4,762 setlines, 111 anchored setlines and 950 drift nets covering {{cvt|488|km|mi}} on the upper Yangtze River, most of which lies within the protected area of the [[List of national nature reserves of China|Upper Yangtze National Nature Reserve]]. They did not catch a single fish. They also used [[hydroacoustics|hydroacoustic]] equipment to monitor sounds in the water, but were unable to confirm the presence of paddlefish.<ref name=BBC/> The species is believed to have gone extinct before 2005 and no later than 2010.<ref name="Zhang Jarić Roberts He 2020 p=136242"/> The [[International Union for Conservation of Nature|IUCN]] assessed the species as extinct in 2019, formally publishing this categorisation in 2022.<ref name="iucn status 21 July 2022">{{cite iucn |author= Qiwei, W. |date=2022 |title=''Psephurus gladius'' |volume=2022 |article-number=e.T18428A146104283 |doi=10.2305/IUCN.UK.2022-2.RLTS.T18428A146104283.en |access-date=21 July 2022}}</ref>

==References==
{{Reflist|30em}}

==External links==

{{Commons category|Polyodon spathula}}
* [https://www.youtube.com/watch?v=FONx-LEly0k The Paddlefish: An American Treasure]&nbsp;– documentary chronicling the biology and life history of paddlefish
* [https://news.cornell.edu/stories/2011/10/most-vertebrates-descended-ancestor-sixth-sense Study: 96 percent of vertebrates descended from common ancestor with 'sixth sense']

{{Chondrostei|state=collapsed}}
{{Acipenseriformes}}
{{Taxonbar|from=Q827142}}
{{Authority control}}

[[Category:Polyodontidae]]
[[Category:Freshwater fish of the United States]]
[[Category:Fish of Canada]]
[[Category:Fish described in 1792]]
[[Category:Articles containing video clips]]