Look at the color and markings, the fin shapes and sizes, and the construction of the head to identify the species of a catfish. The primary catfish species found in North American waters include the channel, blue and flathead catfish.
Channel catfish are typically olive brown to grey in color and often have dark spots. Blue catfish can range from white to dark blue but rarely have spots, and flathead catfish have a mottled brown, yellow and black coloring. The anal fin on a channel catfish is long and curved with between 24 and 29 rays. A flathead has a short rounded anal fin with less than 30 rays. Blue and channel catfish have a deeply forked tail while a flathead's is only slightly notched.
Flathead catfish have broad flat heads with a protruding lower jaw. Channel catfish heads are less flat and the upper jaw protrudes, and blue catfish jaws align on its more symmetrical head.