This explains why the most successful flathead anglers do most of their fishing after dark. Blues, like channel catfish, abound in tailrace areas because of the ample food supply usually found there. They roam about in large schools, feeding at any depth. Adults feed mainly on fish but also will take insects, crayfish and clams. Throughout much of the South, the blue's diet consists almost entirely of gizzard and threadfin shad.
Blue cats feed at any time of the day or night.
But in contrast to other catfish species, they're more likely to continue feeding when water temperatures dip into the 40s. Blues also differ from other catfish in that they are more migratory. They usually swim upriver during the pre-spawn period, congregating in huge schools below dams that block their spawning run. Some remain in the tailwaters through the summer, but as the water cools in late fall, they move downriver and seek out deep holes.