I haven't 'seen' them eat anything, but assume they are eating them because when I bait a hook with trout heads, tails, etc. they hit pretty quickly. Usually what is left when I get the trout is the head, caudal fin, some belly fat portions, etc. Essentially whatever is left after the filets are removed. The gill section is pulled out when the whole fish is left for marketing. And the catfish love to eat that section, so I frequently use that for bait.
