Dipper

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Dipper
A paddlefish (Polyodon spathula)

A paddlefish ( Polyodon spathula )

Systematics
Class : Ray fins (Actinopterygii)
Subclass : Cartilage organoids (chondrostei)
Order : Sturgeon (Acipenseriformes)
Family : Paddlefish (Polyodontidae)
Genre : Polyodon
Type : Dipper
Scientific name of the  genus
Polyodon
Lacépède , 1797
Scientific name of the  species
Polyodon spathula
( Walbaum , 1792)
Berlin special postage stamp from 1977

The spoonbill sturgeon ( Polyodon spathula ) is the only species of the monotypical genus Polyodon . The family of the spoonbill sturgeon (Polyodontidae) is compared to the sister taxon sturgeon (Acipenseridae) and comprises only one other monotypic genus in addition to the genus Polyodon . Its appearance is very different from that of the real sturgeon, which is why it was originally thought to be a kind of freshwater shark. It is 1.5 to over 2 meters tall.

The genus Polyodon has been known since the Upper Cretaceous and for a long time was only described in fossil form. However, larvae of Polyodon spathula were not discovered on the banks of the Mississippi until 1932 and do not have a frontal process. It is interesting that they still have small teeth that the adult specimens no longer have.

Appearance

The forehead is drawn out into a mighty extension. This flattened, flexible structure reaches about a third of the total length of the fish. The completely unscaled skin can be covered with individual small grains of bone, only a few ganoid scales can be found on the upper lobe of the asymmetrical ( heterocercial ) caudal fin .

nutrition

The paddlefish feed on small crustaceans and plankton, which it sifts from deep water with enlarged gill extensions.

Occurrence

The up to six feet long paddlefish used to be widespread across the Mississippi River basins . Dams, water pollution and predatory fishing have brought it to the brink of extinction, not least because the meat and roe of the paddlefish are considered very delicate. In the past few decades, various projects have been tackled to commercially breed paddlefish in ponds.

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