Southern flounder are found in coastal waters of the western Atlantic Ocean, from North Carolina to the mouth of the Rio Grande River and southward into Mexico. In the Gulf, they’re usually found west of the Mississippi River. Southern flounder is mainly an inshore species but lives in a variety of habitats, depending on gender, life stage, and environmental factors. Larvae hatch offshore in the water column; currents transport them inshore to shallow estuaries and tidal rivers. Juveniles settle in shallow, grassy areas of estuaries where food is abundant. Adults spend the warmer months over muddy bottoms in upper estuaries and the fall and winter offshore (for spawning).
Small flounder grow rapidly and can reach one foot in length by the end of their first year. Males seldom exceed this size, but females can grow up to nearly three feet long and 20 pounds. Most flounder harvested in the fishery are one to five pounds. Southern flounder can reproduce at two years of age. When waters start to cool in the fall, they migrate out to offshore Gulf waters to spawn. Between November and January, females spawn every three to seven days, producing thousands of eggs each time. Male southern flounder rarely live past age three; females can live up to about seven years.
With flat bodies and camouflage coloration, adult southern flounder are able to lie on the bottom and ambush their prey. They primarily feed on other fish (striped mullet, spot, and mummichog) but also eat crustaceans, including shrimp and blue crabs. Larvae feed on microorganisms in the water column; juveniles prey on various invertebrates.
Southern flounder are a flat, oval-shaped fish. They spend most of their life lying and swimming along the bottom on their side. Their right side (underbelly) is white, and their left, or top, side is brown with dark and light spots. The coloration on their left side can change to match their habitat, making them nearly invisible. Both eyes are on the left side of its body—when flounder larvae hatch, they have an eye on each side like other fish, but when they develop into juveniles, their right eye moves across the top of the head to the left side. Juvenile southern flounder have large spots that gradually disappear as they grow older, giving them their scientific name Paralichthys lethostigma, meaning parallel fish with forgotten spots.