Tilapia and catfish are good fish to be eating over their carnivorous cousins (food input vs. food output), but the specifics of farm raising have something to do with an individual fish's greenness.

In the end, I hope that we push up production of tilapia here in the US, and I'm excited by programs that blend simple aquaculture with more traditional green growing: http://www.youtube.com/watch?v=9qZPwBPAqks (Will Allen is a boss!).