Appearance. Named for its large, paddle-shaped snout known as a rostrum, the paddlefish is one of Minnesota's largest native fish species. An adult paddlefish in the state is typically 50 inches long and weighs about 40 pounds, though some can exceed 7 feet in length and weigh more than 60 pounds. The paddlefish has a skeleton made of cartilage rather than bone. It has a bluish to dark gray back and sides and a white underbelly.
Range and Habitat. Paddlefish are native to the Mississippi River watershed from Minnesota to the Gulf of Mexico. They also swim in the Yellowstone and Missouri river drainages as far west as Montana and in the Ohio River drainage as far east as Pennsylvania. In Minnesota, paddlefish were historically present in the Mississippi River to St. Anthony Falls, the Minnesota River to Granite Falls, and the St. Croix River to Taylors Falls. Today the state's primary populations are found in the St. Croix and the Mississippi, particularly in deep areas with sluggish current, oxbow lakes, backwaters, and river lakes such as Lake Pepin.
Life Cycle. Male paddlefish in Minnesota reach sexual maturity at 7 to 9 years old; most females mature between 9 and 12 years of age. Spawning occurs in early spring over gravel bars and in flooded tributaries when water temperatures are about 50 degrees. Eggs hatch in seven days or less. Minnesota paddlefish can live longer than 20 years. Adult paddlefish have no predators, but prop strikes from recreational and towboats can kill adult paddlefish. Paddlefish are also hosts to native lampreys and frequently show lamprey scars.
Diet. Paddlefish feed by swimming through masses of zooplankton and straining them out of the water with gill appendages known as rakers. Fisheries biologists think special sensors in the rostrum allow a paddlefish to detect faint electrical currents emitted by clouds of these aquatic microorganisms. In addition to zooplankton, paddlefish will eat aquatic invertebrates and even small fish as they filter feed.
Status. Paddlefish are listed as a threatened species in Minnesota, so recreational and commercial fishing are prohibited. Decline of paddlefish populations, primarily in the early 1900s, was due to habitat loss, overharvest, and other factors. Navigational dams on the Mississippi River restrict movement to spawning habitat. Today, based on observations of fisheries biologists and commercial netters, populations may be increasing. Because silver and bighead carp also feed on zooplankton, paddlefish could face competition for this food source if these invasive species become established here in the Mississippi and St. Croix rivers. By using implantable ultrasonic transmitters to track paddlefish movements, DNR researchers aim to get a better picture of the home ranges of these magnificent native fish.
Michael A. Kallok, online editor