Temporal range: Late Cretaceous–Recent 
|American Paddlefish, Polyodon spathula|
Paddlefish (family Polyodontidae) are primitive Chondrostean ray-finned fishes. The paddlefish can be distinguished by its large mouth and its elongated, spatula-like snout, called a rostrum, which is longer than the rest of the head. These fish are not closely related to sharks, which are in a different taxonomic class, but they do have some body parts that resemble those of sharks such as their skeletons, primarily composed of cartilage, and their deeply forked heterocercal tail fins. The age of this type of fish is hard to determine but many scientists[who?] think that they live 50 years or more.
There are only two modern species of these fish: the Chinese paddlefish (Psephurus gladius) and the American paddlefish (Polyodon spathula). Both have declined greatly in abundance, and the Chinese species may now be extinct. In some areas, paddlefish are referred to as "Spoonbill", "Spoonies" or "Spoonbill Catfish". The American species is Missouri's State Aquatic Animal.
- Subfamily †Paleopsephurinae
- Subfamily Polyodontinae
- Genus †Crossopholis Cope, 1883
- Species †Crossopholis magnicaudatus Cope, 1883
- Genus Polyodon Lacépède, 1797
- Genus Psephurus Günther, 1873
- Genus †Crossopholis Cope, 1883
- Subfamily †Protopsephurinae Grande & Bemis, 1996
The Chinese paddlefish (Psephurus gladius) is (or was) known only from the Yangtze River in China. Nine-foot (3-meter) specimens weighing 300 kilograms (660 lb) have been recorded, and reports of 7 metres (23 ft) fish exist, although the existence of such large specimens is doubtful. They may now be extinct, with a recently completed three-year survey of the Yangtze finding no specimens.
The American paddlefish (Polyodon spathula) is currently known from the Mississippi River watershed in the United States, including slow-flowing waters of the Mississippi River itself, as well as various tributaries including the Missouri River, Ohio River, Yellowstone River, Wisconsin River, Des Moines River, and Arkansas River systems. These fish were also found historically in Lake Erie, in the Great Lakes, but in May 2000, the Canadian Species at Risk Act listed the paddlefish as being extirpated in Canada.
The American paddlefish is one of the largest freshwater fish in North America. They commonly reach 5 feet (1.5 m) or more in length and can weigh more than 60 pounds (27 kg). The largest American paddlefish on record, weighing 144 pounds (65 kg), was caught by Clinton Boldridge in the Atchison Watershed in Kansas. The largest unofficial record was 206 pounds from Lake Cumberland in Kentucky; postcards from the 1960s[which?] show a photo of this huge fish.
Early investigators once thought that paddlefishes used their snouts to dig vegetation from the bottom of lakes and rivers. However, electron microscopy studies refuted this theory when structural similarities of the rostrum’s ampulla (hair cells) to other Lorenzini were noted. In fact, they feed by filtering out zooplankton from the water, using filaments on their gill arches called gill rakers, and in this respect appear similar to the basking shark.
As in many of the distantly related shark class, the paddlefish's rostrum contains electroreceptors that can detect weak electrical fields, suggesting that they use their rostrum as an antenna to detect zooplankton. Even though the rostrum seems to help the fish feed, fish with severely damaged or missing rostrums are able to feed and appear to be just as healthy as other fish with them intact.
The rostrum also helps the fish to feed by acting as a stabilizer. As the fish moves through the water with its mouth open, the rostrum creates lift, much like a wing of an airplane. This helps the fish by keeping its head in a steady position and helps it keep from diving to the bottom.
Paddlefish lay their eggs in midstream over bare rocks or gravel. 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.
Paddlefish were at one time very abundant in most central U.S. river systems, but populations have declined greatly due to overharvesting, sedimentation, and river modification. One of the major reasons for declining paddlefish numbers are the dams constructed on many major U.S. river systems. Paddlefish avoid fish ladders because of the metal rebar used in construction, which disrupts their electro-magnetic sense organs. The dams block paddlefish migration routes that are very important to the fish for spawning.
One other reason for the decreased numbers of paddlefish is overfishing. Pennsylvania Fish and Boat Commissioners are reintroducing the species to historical habitats in the Ohio and Allegheny rivers in an effort to establish a secure breeding population once again. Reintroduction efforts may take many years, since paddlefish mature slowly, lengthening the time required to establish a breeding population. Oklahoma has drastically reduced sportfish harvest of paddlefish to one per person per day to help sustain populations. Paddlefish are a protected species in Wisconsin, where they occur in the Wisconsin River south of the Prairie du Sac hydroelectric dam and in the lower Saint Croix River in Pierce County.
During the last century, paddlefish and sturgeon have been commercially exploited for their eggs (roe), called caviar. Paddlefish and sturgeon are two of the most important fish for freshwater caviar. Paddlefish take many years before they are able to spawn. A female may take nine to ten years, when they are about 42 inches long, and males seven-years-old and 40 inches long are able to spawn. The female releases adhesive eggs over gravel shoals in flowing water. They are capable of producing over a half million eggs a year (up to 25% of her body weight,), but they may not spawn every year.
The Oklahoma Department of Wildlife Conservation (ODWC) set up a Paddlefish Research Center on Grand Lake in Northeast Oklahoma. ODWC biologists record length and weight measurements, and cut a portion of the lower jaw to determine age. To encourage participation, ODWC offers fish cleaning and preparation services, returning the cleaned fish in heat-sealed packaging, and has offered key tag souvenirs. ODWC keeps the eggs (roe) for licensed resale; the proceeds support fish and wildlife programs statewide, without expense to the public. The Paddlefish Research Center also serves as the hub for paddlefish research and management projects throughout Oklahoma.
The Glendive Chamber of Commerce & Agriculture in Glendive, Montana sells Yellowstone Caviar. This caviar is harvested paddlefish caviar that is processed from fish caught at Intake Fishing Area. The Intake Fishing Area is a fishing access site about eighteen miles north of Glendive in Eastern Montana. This caviar has been harvested since 1989 with 70% of the proceeds going to the Glendive Chamber of Commerce & Agriculture and 30% going to the Montana Department of Fish, Wildlife and Parks.
Paddlefish are targeted by poachers for their valuable eggs, and are protected by law over a large part of their range. Habitat destruction is also causing their numbers to decrease more rapidly. Paddlefish need free-flowing rivers that have shallow pools with sandy, rocky bottoms for their spawning. Water temperature is also important for spawning. Modification of rivers by the construction of dams, dredging, and water removal for agricultural use reduces paddlefish spawning grounds.
Free-flowing lakes with reservoirs can also provide paddlefish breeding habitat. One such area is the Missouri River-Lake Sakakawea system in North Dakota. This area is capable of producing good paddlefish numbers because it is a free-flowing system with many good areas for paddlefish to spawn.
Fishing for paddlefish
|This section needs additional citations for verification. (February 2010)|
In most of its range the paddlefish is a protected species, and fishing for paddlefish is illegal in many areas. Any paddlefish caught accidentally should be released unharmed as quickly as possible. However, a few states still allow sport fishing for paddlefish. Because paddlefish are filter feeders, they do not take conventional lures. Taking paddlefish is done with a bow and arrow, a spear, or by snagging (deliberately foul-hooking the fish in the fins or tail). Snagging is the usual method.
Poachers also use these methods to target paddlefish in areas where paddlefish fishing is not legal. Suspect paddlefish fishing activity can be reported to fish and wildlife officers who will verify legality. Some jurisdictions pay a financial reward to citizens whose report leads to prosecution of a poacher. One example is the Iowa DNR, and their Turn In Poachers (TIP) Program which was started in August 1985. The private TIP organization was established by concerned sportsmen and women under the guidance of the Iowa Department of Natural Resources Law Enforcement Bureau. Both groups recognized the need for an added dimension to fish and game law enforcement in the State of Iowa to aid in the fight against poaching.
- Froese, Rainer, and Daniel Pauly, eds. (2009). "Polyodontidae" in FishBase. January 2009 version.
- Revkin, Andrew C. (2009-09-30). "For Chinese Paddlefish, a Long Goodbye". The New York Times. Retrieved 2010-05-20.
- Nachtrieb, H (1910). "The Primitive Pores Of Polyodon Spathula (Walbaum)". The Journal of Experimental Zoology 9: 455–468.
- Jorgensen, J; Flock, A., Wersall, J. (1972). "The Lorenzinian Ampullae of Polyodon Spethula..". Zeithschrift fur Zellforschung und Mikroskopishe Anatomie 130: 362–377.
- Wiley, Edward G. (1998). Paxton, J.R. & Eschmeyer, W.N., ed. Encyclopedia of Fishes. San Diego: Academic Press. pp. 77–78. ISBN 0-12-547665-5.
- Scarnecchia, D.L., Gordon, B.D., Schooley, J.D., Ryckman, L.F., Schmitz, B.J., Miller, S.E., and Lim, Y. (2011). "Southern and Northern Great Plains (United States) Paddlefish Stocks Within Frameworks of Acipenseriform Life History and the Metabolic Theory of Ecology". Reviews in Fisheries Science 19: 279–298. doi:10.1080/10641262.2011.598123.
- Paddlefish season ends on Upper Missouri. May 17, 2010. Associated Press via Missoulian.com.
- [dead link]
|Wikimedia Commons has media related to Polyodontidae.|
- The Chinese Paddlefish Website - containing many photographs of Psepherus.
- ARKive - images and movies of the paddlefish (Polyodon spathula)
- FishBase entry for Polyodontidae
- USGS UMESC Paddlefish Study
- Stochastic synchronization of electroreceptors in the paddlefish
- Grandfishingreport.com on paddlefish
- Earthwave.org on paddlefish