The flathead catfish is one of the largest fish found in Illinois. Its scientific name comes from the Greek word for “mud fish” (Pylodictis) and the Latin word for “olive-colored” (olivaris), which is fitting because this darkly-colored fish prefers to live in deep streams, rivers, canals, lakes, and reservoirs where the water is cloudy and the current is slow.
Adult flathead catfish are solitary creatures and can usually be found near or under fallen trees, logs, and brush piles. They stay in deeper waters during the day and move into shallower water at night where they prey on other fish—their only food source.
Young flathead catfish usually prefer shallower water and primarily eat aquatic insect larvae. When the young reach around 4 inches in length, they also start to eat small fish.
Flathead catfish spawn from late May through August, when the water temperature is between 75 and 80 degrees. They build nests under cover, like logs, stumps, brush piles, or big rocks. Females lay around 1,200 eggs for every pound of body weight, meaning one nest can contain up to 100,000 eggs. Males protect the eggs until they hatch. Baby flathead catfish form tight schools for several days after hatching. Eventually they swim off, going their separate ways.
Flathead catfish can live to be almost 30 years old.
Flathead catfish are native to rivers and lakes in the lower Great Lakes and Mississippi River basin, but have been introduced for sportfishing opportunities in other parts of the United States.
Predatory fish like flathead catfish may actually become invasive if they are introduced into an ecosystem in which they become a new top predator. For instance, flathead catfish are invasive in Chesapeake Bay in the northeast, and compete with native fishes—including other ecologically and economically important fish like striped bass—for available food.
Flathead catfish are highly prized by recreational anglers throughout their range because of their large size and renowned fighting ability. The world record flathead catfish was caught in May 1998 from Elk City Reservoir, Kansas, and weighed 123.6 pounds. The Illinois record flathead catfish was caught in June 2016 from Lake Sangchris, and weighed 81.4 pounds.