slate-colored above, lighter below; greatly elongated snout, long gill covers and a shark-like mouth; scaleless with a skeleton of cartilage
Mississippi and Missouri Rivers as well as lower reaches of some larger tributaries of the Mississippi
zooplankton, insect larvae
107 pounds - Missouri River, Monona County , March 1981 - Robert Pranschke, Onawa, Iowa
almost all paddlefish are caught by snagging below a dam in the spring
These fish are most often collected and observed in the Great Border Rivers; however, it is not unusual for anglers to take them in the lower portion of the Des Moines, Cedar, Iowa and, Skunk rivers. It was formerly rather common but is now absent in East and West Okoboji Lakes and Spirit Lake.
The color of the paddlefish is slate-gray to gray-blue above, fading to somewhat lighter beneath. They can be easily distinguished from all other Iowa fishes by the immensely elongated snout, extremely long gill covers and shark-like mouth. The skeleton is largely cartilaginous. Jaws and palate of young specimens are covered with numerous fine teeth, but the jaws become large, feeble and toothless as the fish reaches maturity. The body is naked, or scaleless. Paddlefish are in many respects one of the most primitive of fishes but are highly specialized in others. It is a remnant of ancient life, differing from other fishes by its elongated paddlelike snout, long gill covers and shark-like body form. It was formerly abundant in the Mississippi valley, but over-exploitation, changes in environmental conditions, or both, have reduced its numbers to a point where it is no longer common except in certain places along the river.
The large size and bizarre shape have made paddlefish particularly interesting to the layman and scientist alike. Specimens over six feet long have been taken from the state, placing it at or near the top of the list for "big fish" honors. The current state record is a 107-pound fish taken from the Missouri River in Monona County during 1981. Early growth of paddlefish is rapid with the fish reaching 10 to 14 and 21 to 24 inches in their second and third years of life. Seventeen-year-old fish average nearly 60 inches in length and weigh about 37 pounds. Paddlefish are long-lived fish with 20 years being common and 30 years or more not unusual. The larger individual fish are females.
Paddlefish feed primarily on zooplankton and insect larvae. The food organisms are filtered from the water by the gill rakers as the fish swims about with its mouth agape. They have no apparent home range and move about freely in shallow water or near the surface in slow moving current, where foraging conditions are favorable.
Different theories have been forwarded regarding the function of the paddle-like snout. It has been suggested that it is used to stir up the bottom to facilitate feeding, serves as a "rudder" to guide the fish and/or is a sense organ for the detection of food organisms. The paddlefish is not a bottom feeder and the snout possesses an elaborate system of sense organs, making the latter theory appear logical as the primary function of the appendage.
Paddlefish spawn in April and May when water temperature is around 55-60 degrees F. The spawning run up the larger streams is closely associated with periods of high flow. Spawning activity takes place over flooded gravel bars. It is assumed that the female starts spawning in the deeper water and completes a spawning "rush" at the surface of the water at which time rapid agitation of the caudal fin can be seen above the surface of the water. The female is accompanied by one or more males on this rush.
Studies in Iowa indicate that most male paddlefish mature at age VI and VII. Females mature at a greater age and produce approximately 7,500 eggs per pound of body weight. The fertilized eggs are adhesive and attach to the first material they contact. Hatching success is highest on clean-swept gravel where siltation is least and aeration is good. Paddlefish eggs hatch in seven days or less at temperatures of 65-70 degrees F. The larvae begin swimming immediately after hatching and are swept downstream into pool areas.
Commercial fishermen harvest about 100,000 pounds annually in the upper Mississippi River, between St. Louis and the Iowa-Minnesota state line. This figure represents slightly less than one percent of the total commercial food-fish harvest. Sport angling for paddlefish has recently become popular, particularly in tailwater areas in the Mississippi River.