Every once in a while, I will see white tuna on a sushi menu. The flesh is white, and is often served in a roll rather than served atop rice, and it's not as flavorful as good quality maguro. To my skeptical mind, it's a little gimmicky.
What exactly is white tuna? Is it a part of a tuna, or a species of tuna, or not even tuna at all? Stumped.