Sole and flounder are both types of flatfish, and because the texture is similar, they are considered interchangeable in recipes. However, they are two separate species with slightly different looks and tastes.
Sole is a type of flatfish. Dover sole, the most common type, is a member of the Soleidae family. Flounder is also a type of flatfish categorized under Heterosomata.
Both fish are flat, with both eyes on one side of their face so they can hide on the ocean floor and watch for prey. While both are oval in shape, flounder is more rounded.
Sole are most commonly found in the eastern Atlantic Ocean and the Mediterranean Sea, while flounder is found in the northern Atlantic Ocean and the Pacific Ocean.
Both sole and flounder have delicate, flaky flesh and a mild, sweet taste. There are several types of each fish, each with a slightly different flavor, generally considered discernible only by more experienced palates.
Dr. Ben Kim of Health & Beyond recommends you choose both sole and flounder from the north Atlantic Ocean, as this area is less likely to be polluted and the fish will contain lower levels of mercury.