A two-year study of more than 1,200 seafood samples by Oceana, an environmental advocacy group, found that a third of seafood sold in grocery stores and restaurants is mislabeled, the group announced Thursday.
DNA testing of seafood samples between 2010 and 2012 found that 33% were mislabeled according to U.S. Food and Drug Administration guidelines.
The most commonly mislabeled fish were snapper and tuna.
Of the samples labeled as snapper, 87% were mislabeled. More than 30 different species of fish were found to be substituted for snapper, but the most common were rockfish and tilapia.
Oceana said the most egregious substitution for red snapper was tilefish, one of four fish the federal government warns has high mercury levels.
Tuna was mislabeled 59% of the time and most commonly swapped with escolar, a type of mackerel that contains gempylotoxin, a toxin that can cause gastrointestinal problems.
"Our findings demonstrate that a comprehensive and transparent traceability system – one that tracks fish from boat to plate – must be established at the national level," Oceana said in a statement. "At the same time, increased inspection and testing of our seafood, specifically for mislabeling, and stronger federal and state enforcement of existing laws combating fraud are needed to reverse these disturbing trends. "
The group collected samples from grocery stores, restaurants and sushi venues nationally and found that the highest mislabeling rate -- 52% -- occurred in Southern California.
Of the three retail outlets, sushi venues most frequently mislabeled fish at a rate of 74%.
Oceana advises consumers to ask questions about the seafood they purchase and to be skeptical of low prices. "If the price is too good to be true, it probably is, and you are likely purchasing a completely different species than what is on the label," the group warns.