Species Spotlight: Paddlefish
The paddlefish is a primitive fish--a survivor of an ancient fish fauna whose earliest fossil records date from the Late Cretaceous period (70-75 million years ago). Paddlefish were erroneously believed by many North American fishermen to be a kind of catfish. Its nicknames reflect the misidentification--duck-billed cat, shovel-billed cat, spoonbill, spoonbill cat, oarfish, or spatula fish. Early taxonomists described it as a "singular new genus of sharks" due to its tail and mostly cartilaginous skeleton. Pere Marquette, an early Illinois explorer, described it as ". . . a remarkable fish resembling a trout with a large mouth. Near its nose is a large bone shaped like a woman's busk, three fingers wide and a cubit long, at the end of which is a disc as wide as one's hand." Paddlefish are among the most primitive living ray-finned fishes and are related to the sturgeons. Five species are known: three extinct species from western North America, Polyodon spathula in North America, and Psephurus gladius in China.
The paddlefish, Polyodon spathula, is native to the Mississippi River basin and several Gulf Slope drainages where it occurs in warm, medium to large rivers with long, deep sluggish pools. It is also found in backwater lakes and bayous. By the early twentieth century in Illinois it could still be found in the seines of commercial fishermen on the Mississippi and Wabash rivers. On the Illinois River, however, it had already become rare. The paddlefish was formerly of great commercial importance in the state, not for its flesh, which was considered tough and inedible, but for its roe (eggs). Its roe were used in the making of caviar.
Paddlefish are bluish gray to olive-gray above and silvery underneath. They are long and have stout bodies, which are entirely naked or covered with tiny imbedded scales. They have large mouths and elongate and flattened snouts, which are in the shape of a long oar or spatula and are one-third the total length of the fish. Early accounts in the Fishes of Illinois (1908) state that paddlefish attained a weight of more than 150 pounds. At present most adults weigh less than 40 pounds and are around 40 inches in length. Paddlefish eat microorganisms by cruising open water with the lower jaw dropped while water is filtered across their large gill rakers, which strain out the plankton and insects.
There is some speculation on the purpose of the fish's unique snout. An early myth was that it was used for stirring up organisms on the bottom of the river. In reality the snout is covered with sensory structures so it may aid in the detection of food. Or perhaps the snout's broadly flattened form may serve as a forward-positioned hydrodynamic plane, stabilizing the fish due to the drag created by vast amounts of water entering the gaping mouth when the fish feeds.
Paddlefish reach sexual maturity by 7-12 years. The fish assemble in fast water over submerged gravel bars and spawn in the spring when water levels are high. The eggs are nonadhesive until they are fertilized. Once fertilized, the now sticky eggs sink to the bottom and stick to the first object they touch. Hatching is within nine days. Early development is rapid and the larvae are soon swept into downstream pools. Their snouts do not begin to grow until two to three weeks after hatching.
Today the paddlefish has been extirpated in parts of its North American range and is severely reduced in other parts due to impoundments, channelization, siltation (particularly of spawning grounds), pollution, and overfishing. They are a "biological treasure of the past and survivor of a primitive family" and hopefully this unique fish will continue to survive in the twenty-first century.
Susan Post, Center for Economic Entomology
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