It’s hard to find a largetooth sawfish in some tropical waters in the Pacific and Atlantic. This long-snouted ray is critically endangered, its numbers dropping fast.

But that hasn’t stopped fishermen from catching them illegally in Brazil, and it hasn’t stopped vendors from mislabeling them as shark, which is legal to sell. In fact, it’s not uncommon for threatened and endangered fish to end up at markets all over the world labeled as another species, according to a new report from the marine conservation group Oceana.

That means that when it comes to fish, going green may be no easy feat. You might think you’re buying a sustainable species for dinner when in reality that fish may be swimming