This morning's Boston Globe has a front-page headlining series of articles on the problem of mislabeled - - shell game, bait and switch [the punning possibilities are endless] - - fish on Boston restaurant menus and in stores.
I think that URL should get you past the pay per view barrier. Otherwise Google it.
Some time ago the NYTimes ran a similar expose of the practice in New York City.
Clearly the problem is endemic to the marketing of fish. So endemic in fact that the popular expressions for this kind of fraud are drawn from fishing, as demonstrated in the opening lines.
For many years I have followed a simple practice that reduces the risk. If more consumers demanded this method, not only would they less likely be defrauded, they would also get better tasting and cheaper fish.
The simple solution is to boycott filets. Only buy whole fish. If you want a filet, cut it yourself or have the waiter do it in front of you.
Once a fish is cut and sliced there is no simple way of knowing what you are getting. And the lower down the marketing chain of fish transmission the cutting occurs, the more likely that products will be switched. Obviously a lot of consumers get too squeamish too look a fish in the eyeball, or to see the entire carcass, bones and all, laid out on a plate, but that may be the only way to reduce the chances of getting ripped off, and possibly running a risk to your health as well as your wallet, e.g. escolar sold as white tuna.
Some imaginative restauranteurs could establish a niche market, if they specialized in whole grilled or roasted fish. And as for the fillets and steaks that necessarily have to be served because some varieties are simply too large for a single portion, dramatically cut the fillet from the whole fish in front of the diner as part of the restaurant experience.
Otherwise fillet customers are just like pigeons in a poker game.
Of all the major markets in the country Boston is one of the closest to regular supplies of fresh fish. The New England fishing industry has been hurt badly not only because of overfishing, but also because of fraudulent mislabelling that encourages cheap frozen imports. If local restauranteurs committed themselves to whole fish service, they would help reduce fraud and help an important New England industry.