"Fake" fish (cheaper fish sold as something more expensive) is apparently fairly common in restaurants and grocery stores.
https://www.cnbc.com/2018/09/21/the-...r-seafood.html
For years, Long John Silvers and Red Lobster were selling "lobster" that was really langostino, which is also known as a squat lobster, but actually isn't a lobster. Now they have to call it "langostino lobster," which is still misleading since it really isn't lobster.