Paddlefish (Polyodon spathula) skull
17 3/4 inches x 3 3/8 inches (greatest width at tip)
Commonly referred to as spoonbill catfish, the paddlefish is not at all related to that group of fish. The paddlefish is a primitive fish whose only living relative is a large fish (Psephurus) that lives in the larger rivers of China. Only a few fossil paddlefish have been found.
Like another ancient group of fish, the sharks, paddlefish have a largely cartilaginous skeleton. They may attain a weight of 150 pounds, but in Minnesota 50 pounds is about the maximum weight recorded. The species has decreased in number, especially in the Upper Mississippi River, since it has been subjected to pollution and heavily exploited for its excellent flesh and roe. Although protected in Minnesota, the paddlefish is still taken under regulated fishing from the central Mississippi and Missouri Rivers.
The head of the paddlefish is very unique, the "bill" being a particularly extraordinary structure the function of which is not entirely understood. It is commonly believed that it is used for stirring bottom sediments in search of food; but its delicate structure suggests this is improbable. The "bill" is richly endowed with sensory organs, which most likely enables the fish to locate its prey (mainly plankton). When swimming, the paddlefish swims with its mouth wide open and moves its "bill" from side to side. Tiny plants and animals are filtered from the water by fine gill rakers in the process.
This particular specimen was kept by the Minnesota Department of Natural Resources and used for live exhibition at the Minnesota State Fair until it died in August of 1979. It was probably caught originally in the St. Croix River.