Want to make sure that the fish we love is around the next time we want it?  Lead by example.  Check out the websites below to make conscious food choices.  For the heck of it, check to see if the info on the sites is supported on other sites.  

Though few of us can personally vouch for the validity of what appears on websites, I once read that striving to be virtuous, responsible beings is virtuous enough.  Just being conscious and aware may be a step in the right direction.

Sushi

http://www.montereybayaquarium.org/cr/cr_seafoodwatch/sfw_sushi.aspx

look on the right side of the page where it says "Sushi Guide".  Click on Best choice, Good alternative, and Avoid for a quick guide as to which choices are eco-friendly.

Seafood search 

http://www.montereybayaquarium.org/cr/SeafoodWatch/web/sfw_factsheet.aspx

Seafood recommendations

http://www.montereybayaquarium.org/cr/cr_seafoodwatch/sfw_recommendations.aspx

recommendations on what to buy and eat at restaurants.  includes links for downloading USA-specific guides on ocean-friendly fish choices.  Check to see about similar guides for countries and regions around the world.

2009 Culinary chart of alternatives (to fish on the avoid list)

http://www.montereybayaquarium.org/cr/cr_seafoodwatch/sfw_alternatives.aspx

fish marked with red stars are said to have high amounts of mercury...treat them as if they're DANGEROUS!...in my humble (yet emphatic) opinion.  i'm joking yet a bit serious.  in all cases, i advocate us all to do our own research and trust our instincts...even if i say something is "DANGEROUS!", in jest or otherwise.

Lastly, click around the site to see the other goodies of information housed there...including a list of restaurants in the Monterey Bay area of California that serve mostly eco/ocean-friendly fish.  Buen Provecho! (that a Spanish version of "Bon appétit".