Flounder (also; fluke) are flatfish that live in ocean waters ie., Northern Atlantic and waters along the east coast of the United States and Canada, and the Pacific Ocean, as well. While flounders have both eyes situated on one side of the head, they are not born this way. Their life involves metamorphosis. During metamorphosis, one eye migrates to the other side of the body so that both eyes are situated on the upward-facing side of its body. After metamorphosis, flounder lie on one side on the ocean floor; either the left or right side might face upward depending on the species.
L. Brent Vaughan Hill's Practical Reference Library Volume II (NewYork, NY: Dixon, Hanson and Company, 1906)