Description: 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 scale less.
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 paddle like 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 112-pound fish taken
from the Grand River behind Grand Lake. 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
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 6 and 7.
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
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 tail water areas below Oklahoma lake dams.