Last year, the New York Times ran a great article on tilapia, the most-eaten farmed fish in America. Once totally unheard of, tilapia has come racing into the American diet because it is so easily farmed. From a theoretical point of view, fish farming is a perfect solution to many problems - fish are theoretically leaner than red meat or even chicken, farming fish reduces the pressure on wild populations, and the controlled environment means that the fish are less likely to be exposed to certain environmental pollutants. That said, this industry hasn't been without problems - there are concerns about the environmental effects of fish farming on this sort of scale, as well as the food fed to the fish.
I urge you to read the article, but more importantly, I urge you to check out this nifty little graphic they put together on the omega-3 content of fish. Tilapia, largely because of the diet they are fed in farming, rank extremely low on the list. Additionally, farmed tilapia have a relatively high amount of omega-6 fatty acids - a pro-inflammatory fat that is already extremely plentiful in the American diet. Many of us have been urged by our physicians (and especially our cardiologists) to start eating more fish, but it's looking like tilapia isn't the best choice. As you start eating more fish, I hope this chart helps guide you on your way.