BETHGE: Once you get the hang of it, differentiating between the two is simple. Winter flounder are right-eyed fish, while fluke are left-eyed. Now, if you are anything like me, you'll have forgotten which is which by the time you are done with this sentence. I've come to rely on a more dependable system. Fluke have a large mouth that's full of teeth, whereas winter flounder have a small, soft mouth suited for eating seaworms.