Paddlefish

Paddlefish

Members of the primitive Polyodontidae family of bony fish, paddlefish are distant relatives of sturgeon, whose closest living relatives are gar (see) and bowfin. They are large, slow-maturing, and long-lived freshwater fish of large inland rivers. They have a distinctive appearance and a prehistoric lineage that dates back hundreds of millions of years. They are not related to catfish.

There are only two known species of paddlefish. The American species (P. spathula), which is profiled here, is commonly referred to simply as paddlefish, lives only in the United States in the Mississippi River system and is a threatened species, although it is pursued in some areas by both commercial fishermen and recreational anglers. The other species is the Chinese paddlefish (Psephurus gladius), which is native to the Lower Yangtze River in China.

Paddlefish have been steadily declining in numbers, due to overexploitation in the late nineteenth and early twentieth centuries, habitat degradation (e.g., construction of dams, locks, and other migratory obstructions), and pollution. The life history of this species and its slow-maturing and intermittent spawning have contributed to its vulnerability to these activities.


Paddlefish are protected in some states, and restricted fisheries exist in others. Populations of North American paddlefish that can sustain fishing pressure exist in only a few localities, and poaching is a continued threat. Poaching occurs for the purpose of securing eggs, which are substituted for sturgeon eggs and valuable when made into caviar.

Identification

The paddlefish is almost sharklike in appearance, and if its long paddle extension were cut off, it would look even more like a shark. Unlike sharks or other fish, the paddlefish has a unique, long, paddle- or spoonlike snout. The function of the snout has not been completely determined, although it is highly enervated. Paddlefish are suspected of using their snouts to locate prey, perhaps to stir sediment on the bottom. There are two small barbels on the snout, and the underside is dotted with sensory pits.

The paddlefish also has a greatly elongated operculum flap, an extremely large basketlike mouth, long gill rakers, and a deeply forked tail with a high dorsal fin that resembles a shark fin. Adult paddlefish are toothless, but juveniles have teeth on their jaws. The color is slate gray to purplish above. They have almost white bellies, and the skin is smooth, like that of a catfish, with the only scales being on the caudal peduncles.

Size/Age

Paddlefish may live to be 25 to 30 years old. They often grow to 100 pounds, although the average fish is much smaller. Literature from the past contains reports of paddlefish that grew to more than 200 pounds. World records are not kept for this species by the International Game Fish Association (IGFA) because they are not hooked in the mouth but snagged. Nevertheless, state records show that Montana produced a 142-pound, 8-ounce fish in 1973 in the Missouri River. A 134-pounder from Missouri was over 20 years old.

Life history/Behavior

Adults migrate upstream to gravel bars in the spring, spawning in high currents with temperatures between 50°F and 60°F. They are commonly found in tailwaters below dams, which impede their upstream migration. In rivers where they are able to travel unimpeded, paddlefish may migrate significant distances.

Spawning occurs in midstream, and the adhesive eggs attach to the gravel on the bottom. When hatched, the fry are moved downstream by swift currents into deep pools with lower water velocities. Where oxbows occur, they may serve as alternate spawning sites and important nursery areas for young paddlefish, whose early growth is rapid.

Food and feeding habits

Paddlefish eat zooplankton, microscopic plants and animals that live in open water. They swim through the water with their large mouths open and strain out the zooplankton with numerous (hundreds) gill rakers. They are not bottom feeders and move about in shallow water or near the surface of slow-moving currents with favorable foraging conditions.

Other Names

spoonbill, spoonbill catfish, spoonbill cat, American paddlefish, Mississippi paddlefish, shovel-billed cat, duckbilled cat, spadefish, shovelfish.

Distribution

The American paddlefish ranges throughout the Mississippi River drainage, from the Missouri River in Montana southward. Some populations are self-sustaining, whereas others are maintained with stocking. American paddlefish have been sent to Russia (50,000 paddlefish eggs were shipped from Missouri in the mid-1970s) in an attempt to establish the species there and to augment caviar production, which has suffered due to dwindling sturgeon populations.

Habitat

Paddlefish prefer low-gradient rivers, pools, backwaters, and oxbows; they also exist in flood-plain reservoirs as a result of dam building. When not spawning, they are pelagic and are found in open water.
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