If we purchase a particular type of fish because we like its taste — say, lemon sole —does it really matter if it's actually summer flounder? Well, yes. Swapping one kind of fish out for another has several implications, some of which could be serious.
Since many forms of fish fraud are perpetrated to allow the fish-seller to increase his profit margins, someone is getting ripped off. It might be the middleman who buys the fish from the seller; it might be the restaurateur or the grocer; or it might be you, the consumer.
Fish fraud also can put all sorts of endangered or threatened species in trouble. Snapper, for example, is currently being overfished. But many swindlers will say their whitefish is snapper. With so much "snapper" in markets and on restaurant menus, people will think the species is thriving, when actually it's not. In addition, some consumers concerned about the health of our oceans carry wallet cards created by groups such as the Monterey Bay Aquarium's Seafood Watch; the cards list fish species to eat or avoid, based on sustainability. Someone trying to eat responsibly could end up downing the very fish she is trying to avoid eating [source: Barclay].
There are also health concerns with fish swapping. King mackerel, often labeled as grouper, is high in mercury; escolar, marketed as white tuna, can cause GI distress due to a naturally occurring toxin it contains. And some fish have allergenic proteins which certain consumers need to avoid. Experts say that such health concerns are generally minor. You might have diarrhea from accidentally eating escolar, but it won't kill you. However, even small risks can become large issues for certain at-risk populations, such as the elderly, children and pregnant women [sources: Barclay, Goetz].