PlanetCatfish.com

Big stomach.
<img src="http://images.yuku.com/image/jpeg/ed225 ... 9964b2.jpg" alt="image"><img src="http://images.yuku.com/image/jpeg/caa15 ... 0b3be6.jpg" alt="image"><img src="http://images.yuku.com/image/jpeg/29515 ... db1f29.jpg" alt="image"><img src="http://images.yuku.com/image/jpeg/fc415 ... 3cc6c0.jpg" alt="image"><img src="http://images.yuku.com/image/jpeg/48c25 ... dbad93.jpg" alt="image">

Could be any number of things: gravid, gut blockage, or even bacteria infection. Keep up the water changes and watch the fish closely.
-Shane

I would fast it for 3 days, and watch to see if it begins to go down. If it does, I would try some shelled peas. To most fish, peas are a laxative.