An important new DNA study by the Oceana Group has found that 60% of the tuna sold in restaurants and grocery stores in the United States is deliberately mislabeled. The fish normally substituted for real tuna is a far less expensive, oily fish, named escolar. This is a fish known to cause diarrhea in humans. But your chances of finding actual tuna when you order it is still better than the odds of receiving authentic red snapper. That fish is misrepresented 87% of the time, according to the study.