Catfish biology and identification

Flathead catfish: The flathead, also called the "mud cat" or "yellow cat," lives in Minnesota's large, slow rivers: the Mississippi below the Coon Rapids Dam, the St. Croix below Taylors Falls, and the Minnesota River. Its name aptly describes its anatomy, which also includes a dark back and brownish mottled sides and a broad, slightly notched tail. It is the largest catfish native to Minnesota; commercial fishermen have reported fish larger than 100 pounds.

The flathead occupies deep pools with dense cover, such as log jams. It feeds primarily on other fish, using its sense of smell and ability to detect vibration through its lateral line to hunt. At night it may more actively feed or even forage in shallow riffles.

On rare occasion a flathead will grab an artificial lure, but usually they are caught on large live bait fish or gobs of nightcrawlers lowered into deep pools or heavy cover. Flathead generally shun the dead baits and "stink baits" so popular for channel cat.

The flathead catfish spawns in summer when the water reaches 72 to 75 degrees. It nests in cavities, such as hollow logs, root wads or log jams in quiet water. After spawning, the male drives the female from the nest - violently if necessary. The male guards the eggs and fans water over them until they hatch and may tend the swarm of young until they disperse.

Though the flathead tolerates turbidity and temperatures in the low 90's, it requires reliable flows of well-oxygenated water.

During the winter, flatheads seek deep waters, where boulders or logs provide refuge from current. There they remain through the winter, so torpid that they may be covered by a fine dusting of silt.

Because flathead catfish eat great numbers of other fish and are good sport fish as well, fish managers have tried stocking them in lakes to control undesirable fish. In one Minnesota experiment, flathead appeared to control carp and black bullhead populations.

Channel catfish: Small channel cats are steel gray and peppered with dark spots; older fish are darker and lack spots. Distinguished from the flathead by its deeply forked tail, a channel cat ranges from 1 to 10 pounds and rarely exceeds 20 pounds.

Though channel cat and flathead coexist in large, slow rivers, the channel cat takes to smaller waters as well, sharing many riffly streams with the walleye and smallmouth bass. The channel cat ranges throughout the Mississippi, Minnesota, St. Croix, Red and St. Louis rivers and many of their tributaries. (The channel cat originally inhabited the Mississippi only below St. Anthony Falls but recently has been introduced as far upstream as St. Cloud. It apparently gained access to the St. Louis River by a connection with the St. Croix River that existed in the waning millennia of the Ice Age.)

The channel cat spawns in early summer when the water reaches 75-80 degrees. Like the flathead, it uses nesting cavities, such as hollow logs, log jams and undercut banks. It requires reliable flows of well-oxygenated water but can tolerate turbid water and temperatures in the high 90s. Murky water, in fact, protects newly hatched channel catfish from sight-feeding predators. During the winter, the channel cat seeks deep water and protection from the current. In big-river wintering areas, channel cat and flathead may be found side by side.

The channel cat is more wide ranging than the flathead. In spring it may move many miles upstream, often into smaller tributaries. It moves downstream again in late fall. Over the course of several years it may move more than 100 miles, even through locks or over dams.

The channel cat feeds on snails, crayfish, aquatic insects, other invertebrates, and small fish. The presence of grasshoppers and other terrestrial insects in its craw indicates it occasionally feeds at the surface. Like the flathead, the channel cat can feed in the dark or in murky water, finding food by smell, touch or sensing vibration. It is much more likely than the flathead to feed on carrion or to take dead bait. On the other hand, it is also far more likely to strike a spinner, plug or jig.

The channel cat is much easier to raise in a hatchery than the flathead. While the flathead eats only live fish, including other flatheads, the channel cat thrives on hatchery pellets. Each year the DNR raises about 30,000 yearling fish at two hatcheries. It is stocked primarily in lakes, where it can become a trophy, growing much larger than it does in streams. Though the channel cat can reproduce in still water, in many lakes numbers are maintained solely by stocking.

Bullhead: Minnesota has three species of bullhead. All are closely related to the larger channel cat, but are better adapted to sluggish creeks and oxygen-poor ponds and lakes. Bullheads tolerate pollution and common fish toxicants better then other fish. The black bullhead, in particular, is "incredibly hardy," said one fish biologist. "All it needs is wet grass. They're one step above rocks."

Bullheads of all three species spawn in late spring and summer, nesting in shallow depressions in sand or mud bottoms. Soon after the eggs hatch, hundreds to thousands of black young swarm near the surface as the parents patrol the margins of the school against predators. Bullheads are omnivorous, feeding on invertebrates and vegetation and some small fish. Bullheads of all species are important prey for walleyes and largemouth bass.

The yellow bullhead is distinguished from other bullhead species by its whitish lower barbels, long anal fin, and rounded tail. It has 24 to 27 anal fin rays, including rudimentaries. It occasionally exceeds 2 pounds. The yellow bullhead lives in many clear, relatively deep, weedy bass-panfish lakes and ponds in central and southern Minnesota. It also occupies slow, southern streams. It requires clearer water than other bullhead species. The yellow bullhead is perhaps the most popular species because of its size and taste.

The brown bullhead is similar in size to the yellow bullhead but has dark lower barbels and a squarer tail. Its anal fin rays total 21 to 24. It has a much more mottled pattern of brown and green than the more evenly colored black bullhead. It also lives in the Mississippi, Minnesota, St. Croix and Red rivers and their tributaries.

The black bullhead has dark barbels like the brown bullhead, but is more uniformly dark rather than mottled. Anal fin rays total 15 to 21. Also, it has a light bar across the base of the tail. Because the black bullhead is more tolerant of oxygen-poor water than any of its relatives, it dominates in warm, eutrophic waters, where other game fish are winter-killed. The black bullhead rarely reaches 15 inches; most are 6 to 10 inches. Nonetheless, black bullhead are often fished for, if only because they are common throughout their range, which includes shallow lakes and muddy streams in central and southern Minnesota as well as the St. Louis River and tributaries of the Red River. It is also common in the Rock River, a tributary of the Missouri, in far southwest Minnesota.