Roughly three-fifths of the tuna sold in US groceries and restaurants is
not tuna.

In 2013, a sampling of the fish sold and used across the United States was
genetically tested to determine what percentage of the "fish" was actually
fish. The test was done by the nonprofit ocean protection group Oceana. Out
of the 1,215 samples, Oceana found that roughly three-fifths of tuna sold
in US grocery stores and restaurants was not actually tuna.

Oceana also found that sushi restaurants were more likely to mislabel their
fish than restaurants or grocery stores. A shocking 74 percent of fish at
sushi restaurants was mislabeled, compared to 18 percent at grocery stores
and 38 percent at other restaurants.