It sounds like you guys have written off this poor fish before it has had a chance
, what is the temp of your tank, ph and have you done any other tests?
If this action started two to five days after it arrived it maybe a simple case of "White spot" in its early stages.
Up the temp of your tank for starters, dont do any water changes until we find out what the water conditions are, if it is "White spot" a water change my help to spread the problem.
White spot is very curable, all water carry the desease, it is stress related bought on by moving or a sudden drop in water temp causing the fish to weaken and sucum to the desease, most aquriums in Australia carry "White spot Cure" of some kind on their shelfs as l am sure they do where you are, remember half strength treatment for catfish good luck
P.S When asking for help with a fish try to give as much detail about the tank conditions and occupants as possible