Flounder are any of numerous species of marine flatfish belonging to the families Achiropsettidae, Pleuronectidae, Paralichthyidae, and Bothidae. Flounder can be found in all major oceans with region differing by species. Many species like the Leopard flounder are widespread throughout the Indo-Pacific. They live in the shallow waters of bays, estuaries, coastal marine areas, rivers and lakes. The substrate may be sandy, muddy or rocky.
When flounders are born, they have bilateral symmetry with one eye on each side of their head, and swim near the surface of the sea. After only a few days though, the fish begins to lean to one side. This triggers a metamorphosis where the eye on that side will migrate to the top side of the fish eventually while staying at the front. The fish’s previous left or right side is now their new top side. Adult fish eventually live on the bottom with their new double-eye side up. The side with theirs eyes is called the “ocular” side. Their eyes can rotate 180 degrees, acting like periscopes to view their surroundings. The family Pleuronectidae consists of approximately 100 different species of flounder. Flounders of this family typically have their eyes and coloring on their right sides. The families Bothidae and Paralichthyidae contain more than 240 different species of flounder. These flounders will typically have their eyes and coloring on their left sides.
Flounders lose the color on their underside as they mature. Some flounder species can grow as large as 3 feet in length. As anguilliform swimmers, flounder swim using only their bodies and caudal fin. Younger flounder feed on small fish and small invertebrates including shrimp, insects, worms and crabs. An adult flounder’s diet consists mainly of small fish such as mullet, anchovies and menhaden. They will still consume the occasional invertebrate as a supplement. Southern flounder are near-top predators in shallow water environments that control the populations of other shallow water species. Some species like the southern flounder can change their color pattern to mimic the substrate. They may also partially buries themselves like the Leopard flounder. This helps with camouflage and ambushing unsuspecting prey while lying flat and still against the bottom.
Flounder are a popular catch fish both due to their tasty flesh and the ease of catching them. However, the populations are well maintained due in part both to management practices as well as the species’ reproductive biology. Southern flounder females will lay more than 9,000 eggs at once. Summer flounder will lay anywhere between 460,000 and 4 million eggs. Fish and Wildlife Conservation (FWC) regulations as of March 1st, 2021 for Gulf flounder, Southern flounder, summer flounder and fringed flounder include a minimum size limit of 14” in total length, 5 bag limit per person and no fishing from October 15 through November 30th. The FWC allows the use of spears, gigs, hook and line, seine and cast nets. Snatching is prohibited, as is the use of any multiple hooks in conjunction with live or dead natural bait.