WARNING: Fish gore...It is okay NOT to view this tutorial if the depiction of animal processing for consumption bothers you.
Here is a quick and easy way to clean/skin bullhead or catfish. With a sharp knife cut along the dorsal (back of fish) to main dorsal fin. BE CAREFUL to not get finned by the side or this main fin. Catfish have strong and sharp barbs on this fin that are very painful if mis-handled.
At the base of the main dorsal fin cut downward at an angle towards the head to cut just through the spine. Bend the head down as you insert your finger(s) or pliers to grip the spine and back. Pull the head downward firmly. The innards and skin should pull away from the meat. Clean out any left over innards from belly cavity. Wash what is left, which should be nothing but meat.