For many years, eating fish has seemed like a no brainer: it's "healthy" and abundant. It turns out that factory raised fish is unhealthy (ever seen photos? they are as ghoulish as the photos of factory farm chickens and beef), and that many wild fish are being overharvested. It's hard to know which fish are sustainable and which are not. A few quick fixes for lack of knowledge/understanding include:
1. Go to the Monterey Aquarium's Seafood Watch site. I myself picked up a nifty wallet-sized guide to carry around with me as I shop and eat out.
2. Check out Slow Food USA's most recent issue of the Snail, all about this topic. www.slowfoodusa.org
3. Read the book "The End of the Line: How Overfishing is Changing the World and What we Eat," by Charles Clover.
4. Read this recent NY Time Editorial: http://www.nytimes.com/2007/06/27/opinion/27weds4.html and think twice about how and how much sushi you are eating. Fashionable, yes. Sustainable, no.