channel cats have a longer fin on the underside that runs in front of the tail,are light in color. flatheads have a flat head and a larger mouth, flathead feed mostly at night and are sometimes called a yellow cat and have a more rounded anal fin. the bullhead is shorter, has a bull head, has a rounded anl fin and is darker

I don't know much about flatheads but I can always tell by the tail. Channel cats have a forked tail and bullheads have a round tail. If you look at my profile you can see the two. The little ones are bullheads and the bigger one on the ground is a channel.