"Channel catfish have a deeply forked tail and dark spots. The spotting, however, diminishes with age. Consequently, older channel cats are frequently mistaken for as blue catfish. But the anal fin on blue cats has a flat outer edge and channels have a rounded edge. If that doesn’t tell them apart look into the gut. A channel catfish has an air bladder that’s divided into two sections. The blue catfish’s air bladder has only one chamber. Young channel catfish are silvery blue-gray and their coloration darkens with age."
