You might think twice before you eat that slab of tuna sashimi. A recent study revealed widespread fraud in sushi labeled as “tuna,” finding that oftentimes restaurants sold sushi made from endangered species or from species dangerous to human health.

In fact, the study found that sometimes that “tuna” isn’t tuna at all.

“A piece of tuna sushi has the potential to be an endangered species, a fraud, or a health hazard,” wrote the authors of the study, which was recently published in PLoS ONE. “All three of these cases were uncovered in this study.”

Scientists from Columbia University and American Museum of Natural History conducted the study by genetically testing samples from sushi they ordered at various sushi joints. 

According to the report, which took 68 samples from 31 restaurants in New York City and Denver, 19 restaurants were unable to clarify, or misrepresented, the type of tuna they were selling.

Five out of the nine samples sold as “white tuna,” were actually escolar, a species banned for sale in both Italy and Japan for health concerns. 

Nineteen of the samples were northern bluefin tuna, which is a critically endangered species. Half of the restaurants selling this type of tuna did not specify it on their menu.

The study not only illustrated the lack of transparency in the sushi marketplace and exposed potential public health risks, but it will also help scientists build a database of fish genes. According to Wired, a coalition of labs has been uploading genetic information to a database called FISH-BOL.

In August 2008, two high school students gained significant media attention for conducting similar tests. They found that 25 percent of sushi was mislabeled, half of the sushi from restaurants, and 60 percent of grocery store sushi had DNA that did not match up to the species on the label.

Correction: This story originally miscited PLoS ONE as PLUS One.