What are you trying to feed him? If he won't eat floating food then feed him sinking, if he won't eat that try frozen foods or live foods. Earthworms, small crayfish, frozen bloodworms, krill etc.
keep the lights off for at least 48 hours and get water movement on the top of the water.... put something like a log at the bottom he can hide under with the gravel. earthworms are a good bet along with fingers! lol.... good luck.
My bullhead started as a tiny fry, I didn't see him eat until he was 7". Drop some food in at night of the sinking variety, I don't believe there ever was a bullhead that starved to death.