The American paddlefish (Polyodon spathula) lives in the slow-flowing waters of the Mississippi River, Missouri River, Yellowstone River, Ohio River and Oklahoma River systems (and was historically found in the Great Lakes). 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 or more in length and can weigh more than 60 pounds. The largest American paddlefish on record was caught in Iowa and weighed 198 pounds. However, the largest unofficial on record was 206 pounds from Lake Cumberland in Kentucky. Postcards from the 1960s show a photo of this huge fish. This type of fish's age is hard to determine but many scientists think that they live 50 years or more.
Fossils of other paddlefish have been found. One such species is Crossopholis magnicaudatus. C. magnicaudatus has been found in the Green River Shale deposit of Wyoming and dates to the Eocene.
Physical characteristics - Early investigators once thought that the paddlefish used their snouts to dig vegetation from the bottom of lakes and rivers long ago, although today's investigators now know that they feed by filtering out zooplankton (Leptodora kindtii) organisms from the water, using filaments located on their gill arches called "gill rakers". While the fish is swimming throughout the water with its mouth open, the food is caught in these rakers which then the fish can digest. A recent study that has been conducted demonstrated that a paddlefish has electro sensory receptors in its rostrum that can detect some 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, it has been observed that fish with severely damaged or missing rostrums are able to feed and are 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.
Caviar harvest - During the last century, paddlefish and sturgeon have stimulated the world stock trades with 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 9 to 10 years, when they are about 42 inches long, and males 7 years old and 40 inches long are able to spawn. When able to spawn, the female releases adhesive eggs randomly over the water bottom and abandons them. They are capable of producing over one-half million eggs a year, but they may not spawn every year.
Current threats - Due to the value of their eggs, paddlefish are a constant target for poachers, and they are subsequently a protected resource over a large part of their range. Additionally, in many of the 22 states that paddlefish reside, habitat destruction is causing their numbers to decrease more rapidly. Paddlefish need free flowing rivers that have shallow pools with sandy, rocky bottoms. These types of areas are perfect for their spawning. Water must also be at the right temperature for the fish to be capable of spawning. Since today's rivers are constantly being modified by the construction of dams, dredging, and excessive water removal for farming purposes, these types of areas are hard for the paddlefish to locate. In some areas, free flowing lakes with reservoirs are sometimes able to provide paddlefish with the right breeding habitat. One such area like this 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 in violation of local fishing regulations in some states is a felony.
Fishing for paddlefish - In some states, paddlefish are abundant enough to allow for sport fishing. Taking paddlefish is done with a bow and arrow, a spear, or by snagging--because paddlefish are filter feeders, they cannot be caught with conventional lures. For snagging, typically, anglers use a large treble hook (2/0 to 4/0 in size), weighted heavily to pull the hook to the bottom. Heavy duty rods, 7' to 15' in length with a heavy duty reel and line, complete the rig, which the angler moves in a sweeping motion to hook the fish in the fins or tail.