I would do a 50% wc right now, and every other day for at least a week. Clean the mech media in your filters, raise the temp to 83-85 and add 1.5 tbps of salt for every 5 gallons of water. You may want to try to find a dedicated catfish forum, sign up and post there. Maybe hit up the bottom dwellers section and post there too. Whatever it is (something I've never seen before) doesn;t look good. Any other symptoms? Is he bloated at all? How's his poo look, brown/tan or white?