In the United States and several other countries, tilapia (catfish) are farmed. The product retails at low prices and it’s promoted as a healthy food. For some reason, I’ve never seen it here in Britain. I’m not expert enough to judge whether or not the ways of farming this species are sustainable. But this New York Times article suggests that it’s not always so.
[Edit] I was wrong to equate tilapia with catfish, as petrel41 points out in a comment below.