Two high school students … took on a freelance science project in which they checked 60 samples of seafood using a simplified genetic fingerprinting technique to see whether the fish New Yorkers buy is what they think they are getting. They found that one-fourth of the fish samples with identifiable DNA were mislabeled. A piece of sushi sold as the luxury treat white tuna turned out to be Mozambique tilapia, a much cheaper fish that is often raised by farming. Roe supposedly from flying fish was actually from smelt. Seven of nine samples that were called red snapper were mislabeled, and they turned out to be anything from Atlantic cod to Acadian redfish, an endangered species.
This is a huge fraud rate. Will diners continue to tolerate it? Probably, yes – I suspect diners care more about affiliating with impressive cooks and fellow diners than they do that fish is correctly labeled.
I saw an investigative report that said here in Florida fish labeled Grouper on restaurant menus is grouper less than half the time. I once had a fish that was supposed to be grouper but did not taste like grouper but I was afraid to make a fuss. I will not go there again because even if it was grouper it was not good grouper. On the other hand if you buy it because you like the flavor and you cannot tell the difference you do not have much to complain about.
1) Although this particular study may be questionable, there are good reasons to believe fish is sytematically mislabeled. My mother-in-law worked at a fish counter for 15+ years and routinely catches restaurants making cheaper substitutions (and shocked when she calls them on it); in NYC a few years ago it was shown that the vast majority of "wild" salmon sold in specialty stores was in fact farmed; etc.
2) There's a difference between not being able to tell the difference because you can't tell the difference and not being able to tell the difference because you've never or rarely had the good stuff.
3) Environmental and health issues are one key to why fish labeling matters. Many disapprove of farmed seafood (usually the cheaper choice) on these grounds. (Imagine I was labeling factory-farmed, hormone-and-antibioticked-up meat as "free-range organic.")