Freshwater September: American Paddlefish



G'day Explorers!  As the month of September continues, as does our theme-month for the Creature of the Week.  Last week we featured the longnose gar.  This week's creature is also an odd shaped and ancient freshwater fish.  For week number two of our Freshwater September month, our creature of the week is the American Paddlefish!

There are only two surviving species of paddlefish in the world: the Chinese paddlefish and the American paddlefish.  Paddlefish are members of the Acipenseriformes order, which also include sturgeons. 1  Though they are members of the class Actinopterygii which include all "bony fish", paddlefish belong to the subclass Chondrostei, whose members have skeletons made primarily of cartilage. 1  However, paddlefish are not sharks.  Scientists believe that the ancestors of the subclass Chondrostei were "bony", but then became mostly "cartilagenous". 2  Also of note, Chondrostei is considered paraphyletic, meaning that this subclass most likely is missing additional descendants from the subclass's common ancestor. 2 

Looking at the picture of a paddlefish, one can see where these fish got their name.  The most distinctive feature of the paddlefish is their long flattened rostrum (or snout). 3  This feature isn't just for looks, however.  The "paddle" is covered with tiny electroreceptors, which act to sense electrical currents. 3  All animals produce various amounts of electrical currents.  Thus, this ability to sense animals, mainly prey, aids the paddlefish in locating food. 3  Further, paddlefish can also sense the electical fields produced by the earth, which aids in migration. 3  Paddlefish also have gill rakers to help filter out the zooplanton upon which they feed. 3  Yes, paddlefish are filter feeders!  The American Paddlefish can grow very large as well, up to 7 feet long, and weigh up to 200 pounds. 1  These fish are also long lived; scientists have found American paddlefish can live for 20 to 30 years, and they believe that American paddlefish could live up to 50 years.  3

The American paddlefish can be found in the Mississippi River at present. 3  Though they are primarily freshwater, paddlefish can also be found in areas of brackish water. 3  These fish inhabit deeper, slow moving river waters with low visibility. 3 

Sadly, the American paddlefish is considered vulnerable due to habitat changes and overfishing. 1  The roe, or eggs, of this animal are considered high quality cavier to many people. 3  Also, due to their size, paddlefish are considered highly prized catches among sportfisherman. 3  Dams in river systems create habitat changes to which these fish cannot adapt, considering they migrate to reproduce. 1

Read more about the American Paddlefish at the following sites:
1. http://en.wikipedia.org/wiki/Paddlefish
2. http://en.wikipedia.org/wiki/Chondrostei
3. Jerome, John http://animaldiversity.ummz.umich.edu/site/accounts/information/Polyodon_spathula.html