رماحيات

Peix espàtula del Mississipi.

Peix espàtula del Iangtsé.

Los poliodòntids, Peixos espàtula, en anglès:Paddlefish, (Polyodontidae) són una família de peixos actinopterigis de l'ordre Acipenseriformes. Són peixos de riu distribuïts per la Xina i Amèrica del Nord. El registre fòssil mostra que són un grupmolt primitiu que aparegué fa més de 300 milions d'anys.

La boca sembla una espàtula i té dues petites barbes, amb dents diminuts.^[1] La pell o té escates excepte unes poques sobre el peduncle se l'aleta caudal heterocerca; fenedures de les ganyes llargues i molt nombroses.^[1]

Són peixos ossis i no estan empàrentats amb els condrictis o taurons, però morfològicament hi tenen certa semblança, ja que tenen esquelet cartlaginós i una aleta caudal semblant.

Gèneres i espècies

• Gènere Polyodon (Lacepède, 1797)
  • Polyodon spathula (Walbaum, 1792) - peix espàtula americà o del Mississipi.
• Gènere Psephurus (Günther, 1873)
  • Psephurus gladius (Martens, 1862) - peix espàtula xinès.

Referències

• Polyodontidae (TSN 161085) al web del Sistema Integrat d'Informació Taxonòmica. (anglès)

• "Polyodontidae". FishBase. Ed. Rainer Froese and Daniel Pauly. febrero 2008 version. N.p.: FishBase, 2008.

Enllaços externs

Schwertstör

Fossil von Protopsephurus liui im Hong Kong Science Museum.

Die Löffelstöre (Polyodontidae (Gr.: poly = viele, odous = Zahn)) sind eine Familie der Störartigen (Acipenseriformes) die nur zwei Gattungen mit je einer Art enthält. Die Arten sind der Löffelstör (Polyodon spathula) aus dem Stromgebiet des Mississippi River (USA) und der Schwertstör (Psephurus gladius) aus dem Jangtsekiang (China). Der Löffelstör ist durch Fischfang, Gewässerverunreinigung und den Bau von Staudämmen in seiner Existenz stark bedroht, der Schwertstör gilt mittlerweile als ausgestorben.

Merkmale

Löffelstöre werden 2,2 bis 3 Meter lang. Berichte über 7 Meter lange Schwertstöre gelten als nicht glaubwürdig. Charakteristisch für die Löffelstöre ist die mächtige ausgezogene Stirnpartie, die einen erheblichen Teil der Gesamtlänge der Tiere ausmacht (bis zu einem Drittel). Erwachsene Löffelstöre sind gänzlich unbeschuppt. Nur die Oberseite des Schwanzflossenstiels und des fleischigen oberen Schwanzflossenlobus ist mit Ganoidschuppen besetzt. Die Zähne sind winzig. Ein Spritzloch ist vorhanden. Am Kiemendeckel befindet sich ein nach hinten gerichteter, großer, spitzer Auswuchs.

Lebensweise

Löffelstöre sind aktive Schwimmer im Freiwasser großer Ströme. Der Löffelstör ernährt sich fast ausschließlich von Plankton, vor allem kleinen Krebstieren – er sondert die Nahrung mittels langer Kiemenfortsätze aus. Der geschlechtsreife Schwertstör geht hingegen dazu über, kleine Fische zu fressen. Das Rostrum (das „Schwert“) dient hierbei offenbar zum Stöbern am Flussgrund. Der Löffelstör laicht in Gruppen über Felsen und Geröll in stark strömendem Wasser. Die Eier kleben am Untergrund.

Stammesgeschichte

Neben den beiden heutigen Arten sind einige ausgestorbene Löffelstöre bekannt. Protopsephurus aus der Unterkreide von China ist der älteste und primitivste Löffelstör und Schwestergattung aller anderen. Paleopsephurus aus der Unter- und Oberkreide von Montana ist die Schwestergattung der verbleibenden Löffelstöre. Weitere ausgestorbene Löffelstöre sind Polyodon tuberculata aus dem unteren Paläozän von Montana und Crossopholis aus dem unteren Eozän von Wyoming. Auch alle fossilen Löffelstöre lebten in Süßgewässern.

Literatur

• Kurt Fiedler: Lehrbuch der Speziellen Zoologie, Band II, Teil 2: Fische. Gustav Fischer Verlag, Jena 1991, ISBN 3-334-00339-6.
• Joseph S. Nelson: Fishes of the World. 4th edition. John Wiley & Sons, Hoboken NJ u. a. 2006, ISBN 0-471-25031-7.
• Peter Bartsch: Actinopterygii, Strahl(en)flosser Seite 226–240 in Wilfried Westheide & Reinhard Rieger: Spezielle Zoologie Teil 2: Wirbel und Schädeltiere, 1. Auflage, Spektrum Akademischer Verlag Heidelberg • Berlin, 2004, ISBN 3-8274-0307-3

Weblinks

– Sammlung von Bildern, Videos und Audiodateien

• Löffelstöre auf Fishbase.org (englisch)

Taxonavigaçion

Polyodontidae

Regno: Animalia (Metazoa)

Subregno: Eumetazoa

Superphylum: Bilateria: Deuterostomia

Phylum: Chordata

Subphylum: Vertebrata

Classe: Actinopterygii

Sublasse: Chondrostei

Ordine: Acipenseriformes

Famiggia: Polyodontidae

Generi: Polyodon - Psephurus

Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae).^[3][4] They are distinguished from other fish by their titular elonglated rostra, which are thought to enhance electroreception to detect prey. Paddlefish have been referred to as "primitive fish" because the Acipenseriformes are among the earliest diverging lineages of ray-finned fish, having diverged from all other living groups over 300 million years ago. Paddlefish are almost exclusively North American and Chinese, both extant and in the fossil record.^[5]

Eight species are known - six extinct species known only from fossil remains (five from North America, one from China),^[2] one extant species, the American paddlefish (Polyodon spathula), which is native to the Mississippi River basin in the U.S., and the Chinese paddlefish (Psephurus gladius), declared extinct in 2022 following a 2019 recommendation that it be declared extinct.^[6][7][8] The species was last sighted in 2003 in the Yangtze River Basin in China.^[9][10] Chinese paddlefish are also commonly referred to as "Chinese swordfish", or "elephant fish".^[11] The earliest known species is Protopsephurus from the Early Cretaceous (Aptian) of China, dating to around 120 million years ago.

Paddlefish populations have declined dramatically throughout their historic range as a result of overfishing, pollution, and the encroachment of human development, including the construction of dams that have blocked their seasonal upward migration to ancestral spawning grounds.^[12] Other detrimental effects include alterations of rivers which have changed natural flows resulting in the loss of spawning habitat and nursery areas.^[13]

Morphology

General morphology of paddlefish

Paddlefish as a group are one of the few organisms that retain a notochord past the embryonic stage. Paddlefish have very few bones and their bodies mostly consist of cartilage with the notochord functioning as a soft spine. During the initial stages of development from embryo to fry, paddlefish have no rostrum (snout). It begins to form shortly after hatching.^[14] The rostrum of the Chinese paddlefish was narrow and sword-like whereas the rostrum of the American paddlefish is broad and paddle-like. Some common morphological characteristics of paddlefish include a spindle-shaped, smooth-skinned scaleless body, heterocercal tail, and small poorly developed eyes.^[11][14] Unlike the filter-feeding American paddlefish, Chinese paddlefish were piscivores, and highly predatory. Their jaws were more forward pointing which suggested they foraged primarily on small fishes in the water column, and occasionally on shrimp, benthic fishes, and crabs.^[11][15] The jaws of the American paddlefish are distinctly adapted for filter feeding only.^[5] They are ram suspension filter feeders with a diet that consists primarily of zooplankton, and occasionally small insects, insect larvae, and small fish.^[5]

Closeup of the head, showing the presence of electrorecepting organs (ampullae of Lorenzini)

The largest Chinese paddlefish on record measured 23 ft (7.0 m) in length, and was estimated to weigh a few thousand pounds.^[10] They commonly reached 9.8 ft (3.0 m) and 1,100 lb (500 kg).^[10][11][16] Although the American paddlefish is one of the largest freshwater fishes in North America, their recorded lengths and weights fall short in comparison to the larger Chinese paddlefish. American paddlefish commonly reach 5 ft (1.5 m) or more in length and can weigh more than 60 lb (27 kg). The largest American paddlefish on record was caught in 1916 in Okoboji Lake, Iowa.^[17] The fish was taken with a spear, and measured 7 ft 1 in (2.16 m) long and 45.5 in (1.16 m) in the girth.^[17] A report published by J. R. Harlan and E. B. Speaker in Iowa Fish and Fishing (1969) said the fish weighed over 198 lb (90 kg).^[18] The world record paddlefish caught on rod and reel weighed 144 lb (65 kg) and was 54.25 in (1.378 m) long. The fish was caught by Clinton Boldridge in a 5-acre pond in Atchison County, Kansas on May 5, 2004.^[19][20] However, the record would be broken an additional two times in 2020. On June 28, 2020, an Oklahoma man caught a 146-pounder in Keystone Lake, west of Tulsa. Later on July 23, 2020, the record was broken again when another Oklahoma man caught a 151-pound, nearly 6-foot long Paddlefish in the same lake.^[21]

Scientists once believed paddlefish used their rostrums to excavate bottom substrate,^[14][22] but have since determined with the aid of electron microscopy that paddlefish rostrums are covered in electroreceptors called ampullae.^[23] These ampullae are densely packed within star-shaped bone projections that branch out from the rostrum.^[24] The electroreceptors can detect weak electrical fields which not only signal the presence of prey items in the water column, such as zooplankton which is the primary diet of the American paddlefish, but they can also detect the individual feeding and swimming movements of zooplankton's appendages.^[5][14] Paddlefish have poorly developed eyes, and rely on their electroreceptors for foraging. However, the rostrum is not the paddlefish's sole means of food detection. Some reports incorrectly suggest that a damaged rostrum would render paddlefish less capable of foraging efficiently to maintain good health. Laboratory experiments, and field research indicate otherwise. In addition to electroreceptors on the rostrum, paddlefish also 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 (gill flaps). Therefore, paddlefish with damaged or abbreviated rostrums are still able to forage and maintain good health.^[5][14]

Habitat and historic range

Over the past half century, paddlefish populations have been on the decline. Attributable causes are overfishing, pollution, and the encroachment of human development, including the construction of dams which block their seasonal upward migration to ancestral spawning grounds. Other detrimental effects include alterations of rivers which have changed the natural flow, and resulted in the loss of spawning habitat and nursery areas. American paddlefish have been extirpated from much of their Northern peripheral range, including the Great Lakes and Canada, New York, Maryland and Pennsylvania. There is growing concern about their populations in other states.

The Chinese paddlefish was considered anadromous with upstream migration, however little is known about their migration habits and population structure. They were endemic to the Yangtze River Basin in China where they lived primarily in the broad surfaced main stem rivers and shoal zones along the East China Sea.^[10][25] Research suggests they preferred to navigate the middle and lower layers of the water column, and occasionally swam into large lakes.^[10] There have been no sightings of Chinese paddlefish since 2003, and were declared extinct in 2019.^[7] Past attempts of artificial propagation for restoration purposes failed because of difficulties encountered in keeping captive fish alive.^[26]

American paddlefish are native to the Mississippi River basin from New York to Montana and south to the Gulf of Mexico.^[27] They have been found in several Gulf Slope drainages in medium to large rivers with long, deep sluggish pools, as well as in backwater lakes and bayous.^[28] In Texas, paddlefish occurred historically in the Angelina River, Big Cypress Bayou, Neches River, Red River tributaries, Sabine River, San Jacinto River, Sulphur River, and Trinity River.^[27] Their historical range also included occurrences in Canada in Lake Huron and Lake Helen, and in 26–27 states in the United States. The Ontario Ministry of Natural Resources listed the paddlefish as extirpated from Ontario, Canada under their Endangered Species Act.^[29] The IUCN Red List lists the Canadian populations of paddlefish as extirpated, noting there have been no Canadian records since the early 1900s and distribution in Canada was highly peripheral. As a species, the American paddlefish is classified as vulnerable (VU) on the IUCN Red List, and its international trade has been restricted since June 1992 under Appendix II of the Convention of International Trade in Endangered Species of Wild Flora and Fauna, or CITES.^[30]

Life cycle

Paddlefish are long-lived, and sexually late maturing. Females do not begin spawning until they are six to twelve years old, some even as late as sixteen to eighteen years old. Males begin spawning around age four to seven, some as late as nine or ten years of age.^[14][31][4] Paddlefish spawn in late spring provided the proper combination of events occur, including water flow, temperature, photoperiod, and availability of gravel substrates suitable for spawning. If all the conditions are not met, paddlefish will not spawn. Research suggests females do not spawn every year, rather they spawn every second or third year while males spawn more frequently, typically every year or every other year.^[14]

Paddlefish migrate upstream to spawn, and prefer 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.^[32] They are broadcast spawners, also referred to as mass spawners or synchronous spawners. Gravid females release their eggs into the water over bare rocks or gravel at the same time males release their sperm. Fertilization occurs externally. The eggs are adhesive and stick to the rocky substrate. The young are swept downstream after hatching and grow to adulthood in deep freshwater pools.^[33]

Propagation and culture

The advancements in biotechnology in paddlefish propagation and rearing of captive stock indicate significant improvements in reproduction success, adaptation and survival rates of paddlefish cultured for broodstock development and stock rehabilitation. Such improvements have led to successful practices in reservoir ranching and pond rearing, creating an increasing interest in the global market for paddlefish polyculture.^[34][35]

In a cooperative scientific effort in the early 1970s between the US Fish & Wildlife Service and its former USSR counterpart, American paddlefish were imported into the former USSR for aquaculture, beginning with five-thousand hatched larvae from Missouri hatcheries in the United States. They were introduced into several rivers in Europe and Asia, and provided the first broodstock that were successfully reproduced in 1984–1986 in Russia.^[36] Paddlefish are now being raised in Germany, Austria, the Czech Republic, and the Plovdiv and Vidin regions in Bulgaria. Reproduction was successful in 1988 and 1989, and resulted in the exportation of juvenile paddlefish to Romania and Hungary. In May 2006, specimens of different sizes and weights were caught by professional fisherman near Prahovo in the Serbian part of the Danube River.^[37]

In 1988, fertilized paddlefish eggs and larvae from Missouri hatcheries were first introduced into China.^[37] Since that time, China imports approximately 4.5 million fertilized eggs and larvae every year from hatcheries in Russia, and the United States. Some of the paddlefish are polycultured in carp ponds, and sold to restaurants while others are cultured for brood stock and caviar production. China has also exported paddlefish to Cuba, where they are farmed for caviar production.^[35]

Classification

Restoration of the Cretaceous †Protopsephurus

There is one currently extant genus in this family, one recently extinct and five extinct genera known exclusively from fossils.

Classification after Grande and Bemis (1991),^[24] with Parapsephurus and Pugiopsephurus added after Hilton et al. (2023):^[2]

• Genus †Protopsephurus Lu, 1994 (Early Cretaceous, China)
  • Species †Protopsephurus liui Lu, 1994
• Genus †Pugiopsephurus Hilton et al., 2023 (Late Cretaceous, North America) (Incertae sedis)
  • Species †Pugiopsephurus inundatus Hilton et al., 2023
• Clade Polyodonti
  • Genus †Paleopsephurus MacAlpin, 1947 (Late Cretaceous, North America)
    • Species †Paleopsephurus wilsoni MacAlpin, 1947
  • Genus †Parapsephurus Hilton et al., 2023 (Late Cretaceous, North America)
    • Species †Parapsephurus willybemisi Hilton et al., 2023
  • Subfamily Polyodontinae
    • Genus †Psephurus Günther, 1873
      • †Psephurus gladius E. von Martens, 1862 Chinese paddlefish (extinct c. 2003)
    • Tribe Polyodontini
      • Genus †Crossopholis Cope, 1883 (Paleogene, North America)
        • Species †Crossopholis magnicaudatus Cope, 1883
      • Genus Polyodon Lacépède, 1797 (Paleocene-Recent, North America)
        • Polyodon spathula Walbaum, 1792 American paddlefish
        • †Polyodon tuberculata Grande & Bemis, 1991

Relationships of the genera, after Grande et al. (2002).^[38]

†Protopsephurus

†Paleopsephurus

†Psephurus

†Crossopholis

Polyodon

References

Pez espátula del Misisipi.

Pez espátula del Yangtsé.

Los poliodóntidos (Polyodontidae) son una familia de peces actinopterigios del orden Acipenseriformes conocidos vulgarmente como peces espátula. Son peces de río distribuidos por China y Norteamérica. El registro fósil muestra que son un grupo muy primitivo que aparecieron hace más de 300 millones de años.^[1]​

La boca es parecida a una espátula (de ahí su nombre) y tiene dos pequeñas barbas, con diminutos dientes.^[2]​ La piel es desnuda, sin escamas, excepto por unas pocas escamas sobre el pedúnculo de la aleta caudal heterocerca; hendiduras de las agallas largas y muy numerosas.^[2]​

Estos peces son óseos y por lo tanto no están emparentados con los condrictios o tiburones, pero tienen algunas partes de su cuerpo muy parecidas a las de éstos, como un esqueleto fundamentalmente compuesto de cartílago y la forma de la aleta caudal.

Géneros y especies

Existen sólo dos especies actuales, de las cuales una se considera extinta:

• Género Polyodon (Lacepède, 1797)
  • Polyodon spathula (Walbaum, 1792) - pez espátula americano o del Mississipi.
• Género Psephurus (Günther, 1873)
  • Psephurus gladius (Martens, 1862) - pez espátula chino.

Especies fósiles:

• † Polyodon tuberculata Grande y Bemis, 1991
• † Hesperopsephurus kyatensis Nessov, 1997
• † Pholidurus disjectus Woodward, 1889
• † Paleopsephurus wilsoni MacAlpin, 1947
• † Crossopholis magnicaudatus Cope, 1883
• † Protopsephurus liui Lu, 1994
• † Psephuroides kazakhorum Nessov, 1997

Referencias

• Sistema Integrado de Información Taxonómica. «Polyodontidae (TSN 161085)» (en inglés).
• "Polyodontidae". En FishBase (Rainer Froese y Daniel Pauly, eds.). Consultada en febrero de 2008. N.p.: FishBase, 2008.

Espatula arrainak Polyodontidae familia osatzen duten Acipenseriformes ordeneko arrain aktinopterigioak dira. Gaur egun bi espezie daude: Mississippi ibaian bizi den Polyodon spathula eta Ibai Urdinean bizi den Psephurus gladius.

Ezaugarriak

Espatula itxurako muturra eta bizar ñimiñoak. Gorputz biluzia (ezkatarik gabea) isats pedunkuluko ezkata gutxi batzuk izan ezik. Isats hegal heterozerkoa. Zakatz-arrastelu luze eta oso ugariak Polyodonen kasuan. Oso hortz txikiak. Espirakulua daukate. Zakatz-operkulua oso hedatua atzerantz ^[1].

Taxonomia

Protopsephurus liui fosilak

Gaur egun familia honetan bi genero daude. Beste lau (edo bost) iraungi dira.

Polyodontidae

• Paleopsephurinae† azpifamilia
  • Paleopsephurus† generoa MacAlpin, 1947
    • Paleopsephurus wilsoni† MacAlpin, 1947
• Polyodontinae azpifamilia
  • Crossopholis† generoa Cope, 1883
    • Crossopholis magnicaudatus† Cope, 1883
  • Polyodon generoa Lacépède, 1797
    • Polyodon spathula Walbaum, 1792 Mississippiko espatula arraina
    • Polyodon tuberculata† Grande & Bemis, 1991
  • Psephurus generoa Günther, 1873
    • Psephurus gladius E. von Martens, 1862 Txinako espatula arraina
• Protopsephurinae† azpifamilia Grande & Bemis, 1996
  • Protopsephurus† generoa Lu, 1994
    • Protopsephurus liui† Lu, 1994

Banaketa

Erreferentziak

Lapasammet (Polyodontidae) sampikalojen lahkoon kuuluva kalaheimo. Sen lajeja tavataan Yhdysvalloista ja Kiinasta makeista vesistä.

Monimuotoisuus ja tuntomerkit

Nykyään lapasampia on vain kaksi lajia, jotka kuuluvat eri sukuihin: lapasampi (Polyodon spathula) ja miekkasampi (Psephurus gladius). Varhaisimmat lapasampien fossiilit on ajoitettu liitukaudelle.

Molemmat nykyljit ovat kookkaita kaloja, lapasampi voi kasvaa yli kaksimetriseksi ja miekkasampi kolmea metriä pidemmäksi., eräiden lähteiden mukaan se voi kasvaa jopa 7 metrin pituiseksi. Kaloilla on pitkä ja kuono, joka on litteä lapasammella ja kapeampi miekkasammella. Kuonon merkitystä ei täysin tiedetä, mutta kalat käyttävät sitä mahdollisesti saaliseläimien tuottamien heikkojen sähkökenttien aistimiseen. Se voi myös vähentää veden aiheuttamaa vastusta lapasampilajien uidessa suu auki. Muita tunnusomaisia piirteitä ovat suurimmaksi osaksi rustosta koostuva tukiranka, pienet silmät ja lähes täysin suomuton ruumis.^{[1][2][3][4][5]}

Levinneisyys, elintavat, uhanalaisuus

Lapasampilajit ovat suurten jokien kaloja. Lapasampea tavataan Mississippijoesta sekä sen sivujoista kuten Missouri- ja Ohiojoista. Miekkasampi on kiinalainen laji ja elää Jangtsejoessa ja eräissä sen lähistöllä sijaitsevissa joissa.

Molemmat lajit ovat pääosin yöaktiivisia. Lapasammen ravinto koostuu eläinplanktonista ja hyönteisten toukista, joita se siivilöi vedestä ja miekkasampi saalistaa kaloja. Molemmat lajit ovat uhanalaisia elinympäristöjen muuttumisen, esimerkiksi patojen rakentamisen vuoksi ja niiden arvostetun mädin, kaviaarin, keräämisen vuoksi. Lapasampi luokitellaan vaarantuneeksi ja miekkasampi äärimmäisen uhanalaiseksi lajiksi.^{[1][2][3][4][5]}

Lähteet

Les Polyodontidae (Polyodontidés en français) forment une famille de deux genres monotypiques de poissons dulçaquicoles appelés poissons-spatule ou polydons^[1]. L'espèce Polyodon spathula est résidente du Mississippi et l'espèce Psephurus gladius du Yangtsé. Cette dernière est déclarée disparue en 2020, après dix ans d'absence dans les eaux de Chine^[2].

Liste des genres et espèces

Selon FishBase :

• Genre Polyodon :
  • Polyodon spathula (Walbaum, 1792)
• Genre Psephurus :
  • Psephurus gladius (Martens, 1862) - espèce considérée éteinte en janvier 2020.

Plusieurs genres connus sont éteints Crossopholis, Paleopsephurus, Protopsephurus.

Voir aussi

Veslokljunke (Polyodontidae), porodica riba iz reda Acipenseriformes^[1] koja dobiva ime po izduženoj njuški. Sastoji se od dva roda, svaki sa jednom vrstom, to su kineska veslokljunka (Psephurus gladius) i američka veslokljunka (Polyodon spathula). Obje vrste su slatkovodne ribe demersalne zone.

Psephurus gladius je endemska u rijeci Yangtze. Američka vrsta živi u sistemu Mississippija, ujključujući i Missouri i Ohio sa pritokama.

Izvori

I pesci spatola (famiglia Poliodontidi) sono Actinopterigi Condrostei primitivi. Si riconoscono per la grande bocca e per il muso allungato detto rostro (becco). Questo muso a forma di spatola raggiunge una lunghezza pari alla metà dell'intero corpo. Ne esistono solo due specie: il pesce spatola cinese (ormai dichiarato estinto) e quello americano. Quest'ultimo è stato dichiarato Animale Acquatico dello Stato del Missouri.

Questi pesci non sono imparentati strettamente con gli squali, ma alcune strutture del corpo, come lo scheletro, composto soprattutto da cartilagine, e la pinna caudale, molto biforcata, sono molto simili a quelle degli Elasmobranchi.

In alcune aree i pesci spatola vengono chiamati "Spoonbill" (becchi a cucchiaio), "Spoonies" o "Spoonbill Catfish" (pesci gatto dal becco a cucchiaio). Le carni di questi pesci sono estremamente oleose, tanto che da alcuni esemplari imbalsamati talvolta fuoriesce una sostanza simile ad olio.

Specie

Il pesce spatola cinese (Psephurus gladius) viveva nel fiume Yangtze. Ne sono stati registrati esemplari lunghi tre metri del peso di 300 kg; taluni parlano inoltre di esemplari lunghi 7 m, sono stati dichiarati estinti nel gennaio 2020.

Pesce spatola americano, Polyodon spatula

Il pesce spatola americano (Polyodon spathula) vive nei lenti corsi d'acqua dei bacini idrografici dei fiumi Mississippi, Missouri, Des Moines, Yellowstone e Oklahoma e in passato si trovava anche nei Grandi Laghi. Nel maggio 2000 il Ministero dell'Ambiente del Canada lo ha dichiarato scomparso da quello Stato. È uno dei più grandi pesci d'acqua dolce nordamericani: può essere lungo più di 1,5 m e pesare oltre 27 kg. L'esemplare più grande mai misurato venne catturato nell'Iowa e pesava 90 kg. Il record non ufficiale, comunque, spetta ad un esemplare di 93 kg proveniente dal lago Cumberland, nel Kentucky, immortalato in una serie di cartoline postali degli anni '60. L'età che può raggiungere questo pesce è difficile da determinare, ma molti scienziati ritengono che possa essere di 50 anni o più.

Oltre a queste due specie, conosciamo anche alcune forme fossili di pesce spatola. Una di queste, Crossopholis magnicaudatus, è stata ritrovata nei depositi di Green River Shale, nel Wyoming, e risale all'Eocene.

Caratteristiche fisiche

I naturalisti del passato ritenevano che i pesci spatola utilizzassero il loro muso per tirare fuori vegetali dal fondo di laghi e fiumi. In realtà, questi pesci si nutrono filtrando lo zooplancton dall'acqua grazie ad una serie di filamenti sugli archi branchiali detti "branchiospine".

Il rostro contiene una serie di recettori in grado di individuare deboli campi elettrici, tanto che è stato suggerito che possano usare questa loro capacità per individuare lo zooplancton^[1]. Tuttavia, sono stati osservati anche esemplari con il rostro gravemente danneggiato o perfino privi di esso in grado di nutrirsi lo stesso e in piena salute.

Il rostro serve anche a stabilizzare la posizione dell'animale durante la nutrizione. Mentre questo si muove nell'acqua tenendo la bocca aperta, il rostro dà origine ad una serie di scie, molto simili alle ali di un aereo. Queste aiutano il pesce a mantenere la testa in una posizione stabile e le permettono di immergersi meglio.

I pesci spatola depongono le uova sopra rocce o ghiaia in zone dove la corrente non è molto rapida. Queste sono adesive e aderiscono bene al substrato roccioso. Dopo la schiusa, gli avannotti seguono la corrente fino a raggiungere stagni più profondi, dove raggiungeranno le dimensioni degli adulti^[1].

Status

Un tempo i pesci spatola erano molto comuni in quasi tutti i bacini idrografici degli USA centrali, ma la pesca incontrollata, la sedimentazione e le modifiche apportate al corso dei fiumi ne hanno ridotto notevolmente il numero. Una delle cause principali del loro declino è stata la costruzione un po' ovunque di dighe: queste bloccano le rotte migratorie dei pesci spatola che devono riprodursi. Un'altra ragione è da imputarsi alla pesca eccessiva. Il Ministero dell'Ambiente della Pennsylvania sta reintroducendo questa specie nei fiumi dell'Ohio e degli Allegheny, dove un tempo viveva, nel tentativo di ricreare una popolazione riproduttiva. Prima che i pesci divengano maturi e possano riprodursi, però, dovranno passare molti anni.

Raccolta del caviale

Nel corso del secolo scorso, i pesci spatola e gli storioni hanno giocato un importante ruolo commerciale grazie alle loro uova, dette caviale. Entrambi questi tipi di pesce sono due dei più importanti produttori di caviale d'acqua dolce. I pesci spatola, però, impiegano molti anni prima di essere in grado di riprodursi: una femmina ne dovrà aspettare 9 o 10, quando avrà raggiunto la lunghezza di un metro, mentre ad un maschio ne occorrono solo 7 per raggiungere la stessa lunghezza. Quando depone le uova, la femmina le rilascia casualmente sul fondo e le abbandona. Un unico esemplare può produrne mezzo milione all'anno, ma non si riproduce tutti gli anni.

Minacce attuali

A causa del valore delle sue uova, i pesci spatola sono un bersaglio costante dei pescatori di frodo e proprio per questo motivo sono protetti in quasi tutto il loro areale. Malgrado le misure di protezione, in molti dei 22 Stati dove risiedono la loro sopravvivenza è minacciata dalla distruzione dell'habitat. Questi pesci necessitano di fiumi non interrotti da sbarramenti collegati a stagni riparati dal fondo sabbioso o roccioso, zone ideali per la deposizione delle uova. L'acqua, inoltre, deve avere una giusta temperatura affinché la deposizione abbia luogo. Dato che al giorno d'oggi i fiumi vengono costantemente modificati dalla costruzione di dighe, dai dragaggi e dagli eccessivi prelievi idrici a scopi agricoli, i pesci spatola riescono a localizzare le aree giuste per la riproduzione con molta difficoltà.

In alcune aree, i laghi artificiali forniscono l'habitat adatto per la riproduzione dei pesci spatola. Una di queste zone è il lago Sakakawea del Dakota del Nord, sul Missouri. In quel lago questi pesci sono piuttosto numerosi, dato che la zona offre molte aree appropriate per deporre le uova. In alcuni Stati pescare i pesci spatola in violazione delle leggi locali è ritenuto un crimine.

Pesca ai pesci spatola

In certi Stati, i pesci spatola sono abbastanza comuni da poterne essere permessa la pesca sportiva. La cattura avviene con arco e frecce o con le reti, visto che essendo animali filtratori non possono essere catturati con i metodi tradizionali. Per la cattura, di solito, i pescatori utilizzano un grosso uncino a tre punte, pesante abbastanza da poter essere adagiato sul fondo. Robuste canne da pesca, munite di un buon mulinello, completano lo strumento, che il pescatore muove in qua e in là con la speranza di poter conficcare gli uncini nelle pinne o nella coda del pesce.

Note

Bibliografia

• "Polyodontidae". FishBase. Ed. Rainer Froese and Daniel Pauly. January 2009 version. N.p.: FishBase, 2009.

Irklanosinės (Polyodontidae) – eršketžuvių (Acipenseriformes) šeima. Kūnas plikas arba odoje yra tik mažyčiai kauliniai grūdeliai. Rostrumas labai ilgas, irklo formos. Žiotys plačios su mažais dantukais, žandų aparatas neiškišamas.

Šeimoje 2 gentys ir 2 rūšys:

• Amerikinis irklanosis (Polyodon spathula). Viena didžiausių Šiaurės Amerikos gėlųjų vandenų žuvų.^[1] Užauga iki 20 m ilgio ir sveria 75 kg. Gyvena Misisipės upėje. Minta planktonu, košdamas vandenį.
• Kininis irklanosis (Psephurus gladius). Užauga iki 7 m ilgio. Gyvena Jangdzės upėje.

Šaltiniai

Lepelsteuren (Polyodontidae) vormen een primitieve familie van vissen uit de orde van de steurachtigen (Acipenseriformes). Kenmerkend van vissen uit deze familie is de grote bek en de langgerekte lepelachtige snuit. Deze snuit neemt de helft van de totale lengte van de vis in beslag. Sommige delen van de vis, zoals het skelet en de diep gevorkte staartvin, lijken op delen van haaien, hoewel ze er niet nauw mee verwant zijn.

Lepelsteuren zijn de oudst bekende vissen, waarvan fossiele vondsten dateren van 300 tot 400 miljoen jaar geleden (50 miljoen jaar vóór het verschijnen van de dinosaurussen). Het lichaam van de vissen bevat een hoog gehalte aan visolie, en zelfs opgezette exemplaren lekken soms nog een olieachtige vloeistof.

Soorten

Er bestaan nog twee levende soorten in de familie van de lepelsteuren: Psephurus gladius en Polyodon spathula.

Psephurus gladius leeft in de Jangtsekiang. Er zijn exemplaren aangetroffen van 3 meter lang die 300 kilogram wogen. De andere soort, Polyodon spathula, leeft in langzaam stromend water van de Mississippi, Missouri, Ohio en de rivieren in Oklahoma. De vis werd vroeger ook aangetroffen in de Grote Meren. In mei 2000 zijn de vissen uitgestorven verklaard in Canada. De lepelsteur is een van de grootste zoetwatervissen van Noord-Amerika en wordt gewoonlijk 1,50 meter lang en weegt dan meer dan 25 kilogram. Het grootste exemplaar werd in Iowa gevangen en woog 91 kilogram. Het is lastig om de leeftijd van exemplaren te bepalen, maar ze worden naar schatting meer dan 50 jaar oud.

Fossiele exemplaren van andere lepelsteursoorten zijn ook aangetroffen, zoals Crossopholis magnicaudatus die gevonden werd in Wyoming en dateert uit het Eoceen.

Kenmerken

Onderzoekers dachten vroeger dat de lepel van de vissen gebruikt werd om bodemvegetatie van meren en rivieren om te woelen, maar nu is bekend dat deze alleen gebruikt wordt voor het filteren van zoöplankton uit het water. Ze doen dit met de kieuwbogen binnen de bek. Verder blijkt de lepel ook te dienen als stabilisator tijdens het zwemmen, waarbij de lepel als een soort vliegtuigvleugel fungeert. Uit recent onderzoek blijkt dat de vissen elektrosensoren bezitten waarmee ze zwakke elektrische velden kunnen detecteren.

Status

Door onder andere overbevissing en dammenbouw, waardoor migratieroutes worden onderbroken en het voor de vissen lastig wordt om de paaigronden te bereiken, is de populatie sterk in aantal afgenomen.

Kaviaar

Net als de kuit van vissen uit de steurenfamilie, wordt ook de kuit van deze vis gebruikt om kaviaar van te fabriceren. Een wijfje heeft 9 tot 10 jaar nodig om eieren te kunnen leggen en legt per jaar meer dan een half miljoen eieren. Ze paaien echter niet elk jaar.

Spadestører er en liten familie av svært primitive beinfisk, beslektet med vanlige stører.^[1] Familien omfatter to nålevende arter og fire fossile. De kan bli litt over 2 meter lange. De likner fysisk på vanlige stører, men mangler det typiske hudpanseret av beinplater som man finner hos dem, og har nesen trukket ut i en lang sverd- eller spadeaktiv utvekst som den bruker til å rote opp bunndyr med. Denne tydelige utveksten har gitt gruppen navnet.

Nyklekte spadestører mangler de voksnes utvekt og likner på vanlige stører i fasongen. «Spaden» eller «sverdet» begynner å dannes kort tid etter at de er klekket.^[2]

Utbredelse og trusler

Spadestørene har en sterkt begrenset subtropisk utbredelse. Spadestøren finnes bare i Mississippi-elva i USA og sverstør er endemisk for Yangtze i Kina.^[3] Begge er skjeldne, og den kinesiske arten regnes som kritisk truet.^[4]

Bestandene av begge arter av spadestører har sunket dramatisk i deres hjemområder som et resultat av overfiske, forurensing og tap av leveområder på grunn av utbygging og særlig bygginger av store demninger som har blokkert den årlige vandringen opp elver for å gyte.^[5] Andre faktorer som har skadet bestandene er store prosjekter (særlig i Kina) der elveløp har blitt lagt om. Dette har ført til et gyteområdene til den kinesiske arten har blitt skadet eller er blitt utilgjengelige. Den kinesiske sverdstøren har ikke blitt observert siden 2007, og det er mulig at arten er utdødd.^[6][7]

Referanser

Eksterne lenker

• (en) Spadestører – oversikt og omtale av artene i WORMS-databasen
• (en) Spadestører i Encyclopedia of Life
• (en) Spadestører i Global Biodiversity Information Facility
• (en) Spadestører hos Fossilworks
• (en) Spadestører hos NCBI
• (en) Spadestører hos ITIS
• (en) Kategori:Polyodontidae – bilder, video eller lyd på Wikimedia Commons
• Polyodontidae – detaljert informasjon på Wikispecies

Denne iktyologirelaterte artikkelen er foreløpig kort eller mangelfull, og du kan hjelpe Wikipedia ved å utvide den.
Det finnes mer utfyllende artikkel/artikler på .

Wiosłonosowate^[2], łyżkowce^[2], jesiotry wiosłonose^[3] (Polyodontidae) – rodzina słodkowodnych, rzadziej słonawowodnych ryb jesiotrokształtnych (Acipenseriformes). Występują w Azji i Ameryce Północnej. Są poławiane dla smacznego mięsa.

Cechy charakterystyczne

Wydłużone, walcowate ciało, niemalże okrągłe w poprzecznym przekroju. Głowa wyciągnięta w bardzo wydłużony ryj (rostrum) w kształcie poziomo ułożonego wiosła, który stanowi wrażliwy narząd czuciowy pokryty licznymi elektroreceptorami. Otwór gębowy z dwoma wąsikami, znajduje się w dolnym położeniu. Uzbrojony jest w drobne zęby. Tryskawka obecna^[4].

Od jesiotrowatych odróżnia je brak tarczek kostnych na skórze. Łuski ganoidalne występują tylko na górnym płacie płetwy ogonowej^[3][4].

Klasyfikacja

Rodzaje zaliczane do tej rodziny:

współcześnie żyjące^[5]

Polyodon – Psephurus

wymarłe^[4]

†Crossopholis – †Paleopsephurus – †Protopsephurus

Zobacz też

• Ryby - wykaz rodzin

Przypisy

Bibliografia

• Joseph S. Nelson: Fishes of the World. John Wiley & Sons, 2006. ISBN 0-471-25031-7.
• G. Nikolski: Ichtiologia szczegółowa. Tłum. Franciszek Staff. Warszawa: Państwowe Wydawnictwo Rolnicze i Leśne, 1970.
• Mały słownik zoologiczny: ryby. Warszawa: Wiedza Powszechna, 1976.

Polyodontidae é uma família de peixes actinopterígeos pertencentes à ordem Acipenseriformes, que inclui os peixes-espátula e é exclusiva de água doce.

Os peixes-espátula têm barbatana caudal bifurcada, corpo sem escamas e um focinho longo, em forma de espátula, que lhes dá o nome. Estes peixes habitam rios de curso lento, permanecendo junto ao fundo onde se alimentam sobretudo de plancton. Os peixes-espátula são peixes de grande porte que podem atingir 3 metros de comprimento.

Peixe-espátula do Mississippi, Polyodon spathula

Espécies

Ambas as espécies são pescadas como alimento e encontram-se ameaçadas de extinção.

• Peixe-espátula do Mississipi (Polyodon spathula) - exclusivo do Rio Mississippi
• Peixe-espátula chinês (Psephurus gladius) - exclusivo do Rio Amarelo

Psephurus gladius

Skedstörar (Polyodontidae)^[1] är en familj av fiskar som ingår i ordningen störartade fiskar.^[1] Enligt Catalogue of Life omfattar familjen två arter i var sitt släkte^[1].

Släkten enligt Catalogue of Life^[1]:

• Polyodon, med arten skedstör (Polyodon spathula).
• Psephurus, med arten svärdstör (Psephurus gladius).

Skedstören förekommer i USA och svärdstören i Kina. Båda arter har en nos som liknar en paddel med flera mycket korta skäggtömmar. De har inga fjäll på kroppen förutom på en liten region på ovansidan. Arterna fiskas för köttets skull. De hölls även i några större akvarier. Det vetenskapliga namnet är sammansatt av de grekiska orden poly (många) och odous (tänder).^[2]

Källor

1. ^ [a b c d] Bisby F.A., Roskov Y.R., Orrell T.M., Nicolson D., Paglinawan L.E., Bailly N., Kirk P.M., Bourgoin T., Baillargeon G., Ouvrard D. (red.) (27 april 2011). ”Species 2000 & ITIS Catalogue of Life: 2011 Annual Checklist.”. Species 2000: Reading, UK. Arkiverad från originalet den 18 juni 2012. https://web.archive.org/web/20120618223324/http://www.catalogueoflife.org/services/res/2011AC_26July.zip. Läst 24 september 2012.
2. ^ Polyodontidae, Fishbase, läst 2017-11-25

Externa länkar

• Wikimedia Commons har media som rör Skedstörar.
  Bilder & media
• Wikispecies har information om Polyodontidae.
  Artförteckning

Cá tầm thìa (Polyodontidae) là các loài cá vây tia nguyên thủy.

Phân loại

Họ này còn 2 loài sinh tồn được xếp vào 2 chi riêng biệt và 4 chi tuyệt chủng: Polyodontidae

• Phân họ † Paleopsephurinae
  • Chi †Paleopsephurus MacAlpin, 1947
    • Loài †Paleopsephurus wilsoni MacAlpin, 1947
      Các hóa thạch Protopsephurus liui
• Phân họ Polyodontinae
  • Chi †Crossopholis Cope, 1883
    • Loài †Crossopholis magnicaudatus Cope, 1883
  • Chi Polyodon Lacépède, 1797
    • Polyodon spathula Walbaum, 1792
    • †Polyodon tuberculata Grande & Bemis, 1991
  • Chi Psephurus Günther, 1873
    • Psephurus gladius E. von Martens, 1862
• Phân họ †Protopsephurinae Grande & Bemis, 1996
  • Chi †Protopsephurus Lu, 1994
    • Loài †Protopsephurus liui Lu, 1994

Chú thích

Bài viết Lớp Cá vây tia này vẫn còn sơ khai. Bạn có thể giúp Wikipedia bằng cách mở rộng nội dung để bài được hoàn chỉnh hơn.

• x
• t
• s

匙吻鲟 Polyodon spathula
白鲟 Psephurus gladius

匙吻鲟科（學名：Polyodontidae）的鱼目前世界上只有两属两种，即生活在密西西比河的匙吻鲟和生活在长江的白鲟。

匙吻鲟科鱼无骨板无鳞，口大無「鬚」，吻向前突出几乎达身长的一半，匙吻鲟的吻是桨状的，白鲟的吻平直如剑，因此也被称为“象鼻鲟”。体长达3米，也有报道捕获7米长的鱼。目前两种鱼都面临绝种的威胁。

外部链接

• 美国政府研究匙吻鲟项目网页

주걱철갑상어류(-鐵甲-類, paddlefish)는 연질어아강에 속하는 원시적인 형태의 조기어류이다.

하위 종

2종의 현존 종으로 이루어져 있다.

주걱철갑상어과 (Polyodontidae)

• † Paleopsephurinae
  • † Paleopsephurus MacAlpin, 1947
    • † Paleopsephurus wilsoni MacAlpin, 1947
• 주걱철갑상어아과 (Polyodontinae)
  • † Crossopholis Cope, 1883
    • † Crossopholis magnicaudatus Cope, 1883
  • 아메리카주걱철갑상어속 또는 폴리오돈속 (Polyodon) Lacépède, 1797
    • 아메리카주걱철갑상어 또는 폴리오돈 스파툴라 (Polyodon spathula) Walbaum, 1792
    • † Polyodon tuberculata Grande & Bemis, 1991
  • 주걱철갑상어속 또는 프세푸루스속 (Psephurus) Günther, 1873
    • 중국철갑상어 또는 프세푸루스 글라디우스 (Psephurus gladius) E. von Martens, 1862

 현재 중국 장강의 지류인 오우강(烏江)에 서식이 확인됨 

• † Protopsephurinae Grande & Bemis, 1996
  • † Protopsephurus Lu, 1994
    • † Protopsephurus liui Lu, 1994