Ok, you should really provide us with more info. Tank size, water temp, water paramaters, everything that rallysman mentioned before. Also what do you try to feed your cat? How long have you owned your catfish? Have you tried feeding him after lights out? How long has your tank been established? How often do you clean/do water changes? The more info the easier it is to help you. If you don't have test kits of your own simply take a bottle of it to your lfs and they should do a free full range test or very cheaply. After you find the results post them here for us to help you. For your info my catfish bang each other up all the time in fights for territory, and also on the large stones I use for their substrate. That brings another question to mind what decorations do you have in the tank and what's your substrate and filtration like? Avoid carbon if at all possible. One of my hybrids had half his tail ripped off by my larger one and it grew back in 2 weeks most of the way.
must have paramaters
wonder if he'll ask what to do again without params!
JK good luck on getting the cat healed up!