If you're picky about the fish you eat—and, let's face it, you should be—then buying fish just got fishier. Actually, the problem has been around for a while, but a new report just confirmed that much of the fish for sale (both at stores and in restaurants) is mislabeled. The problem is most rampant in Los Angeles, where 55 percent of the seafood sampled by Oceana was mislabeled. But Boston (48 percent), New York City (39 percent) and Miami (31 percent) all are plagued by the problem.

Certain varieties were more likely to be incorrectly labeled, including wild salmon, red snapper, white tuna, cod, halibut and sole. What's most troubling about the report is that fish are often substituted by varieties that people are often urged to avoid. For instance, high-mercury tilefish for red snapper, GI-distress-causing escolar for white tuna or less-healthy farmed Atlantic salmon for wild.

Buy fish from larger grocery chains, rather than small independent ones and be wary about sushi restaurants—76 percent of them had fish fraud.