Channel catfish, blue catfish and white catfish are generally larger than yellow, black and brown bullhead catfish. Bullheads differ from other catfish in that bullheads have straight or rounded tails, whereas other species of catfish have forked tails. Coloring between species differs as well.
Channel catfish reach maximum lengths of 30 inches or more, white catfish reach up to 20 inches and the blue catfish is one of the largest catfish species in North America. Yellow bullheads reach a maximum length of 14 inches, black bullheads attain full size at 11 inches and brown bullheads get up to 12 inches long. When these fish reach full size, catfish are longer than bullheads.
Tail shape is another differentiating factor between catfish and bullheads. Channel catfish have deeper forks in their tails than white catfish and blue catfish, and white catfish have slightly forked tails. Yellow, black and brown bullheads have straight, rounded or slightly notched tails, but these fish do not have pronounced forks in their tails.
As their names indicate, bullheads tend to have yellowish, brownish and black markings with lighter colored undersides. Channel catfish are brownish-gray, blue catfish are gray with blue coloring and white catfish appear greenish and gray.