The southern flounder is one of approximately 130 American flatfish species. Southern flounder belong to the family Paralichthyidae. Flatfishes are compressed laterally (flat), with the dorsal side of the body pigmented in order to match their surroundings. Southern flounder are light to dark brown with darker spots and blotches that are not well defined. All flatfishes have eyes that migrate dorsally during larval development, so both eyes are found on the "ocular" side. The ocular side in southern flounder is the left side, but in other flatfishes it may be the right side. The underside of the fish, the ventral or "blind" side, is usually light in color. Maximum adult size in this species is 75 cm (30 in).
Habitat and Biology
Southern flounder are a benthic species found in coastal waters of the southeastern United States, from the Chesapeake Bay to Florida (except southern Florida), and along the Gulf of Mexico. They can tolerate a wide salinity range and commonly inhabit brackish and freshwater habitats. Females grow faster than males; each sex matures as they approach their second birthday (males are 20.3-25.4 cm or 8-10 inches long; females are 30.5-35.6 cm or 12-14 inches long). The average life span of a male is two years, and the oldest male southern flounder reported in South Carolina was age 3+. Females are dramatically larger than males at a given age and a three-year old female may weigh 0.7 to 2.7 kg (1.5 to 6 pounds).
Beginning in late September of each year, southern flounders that are older than one year begin to mature and leave the estuaries for offshore spawning grounds. The locations of these offshore spawning grounds are unknown at this time. Males leave the estuaries and move towards the spawning grounds earlier than females. Their migration coincides with a 4oC to 5oC drop in temperature. Only the young-of-year that are approaching age one remain inside South Carolina estuaries from December through April. After they spawn and water temperatures rise, mature fish re-enter the estuaries. After hatching, the larvae feed and grow near the ocean surface as they are transported toward shore by currents initially associated with the Gulf Stream. The swimming ability of the juveniles, coupled with the presence of tidal currents in near-shore waters, provides a mechanism for the transport of the young to the estuarine nursery habitat. Settling (affiliation with creek bottoms and attainment of adult pigmentation) of the southern flounder occurs in lower and moderate salinity areas of South Carolina estuaries from January through March of each year. This species utilizes the same shallow marsh habitat as the red drum and spotted seatrout as a nursery area. In the shallow tidal creeks they feed on small shrimps and fishes. As they increase in size, fish become the preferred prey. Southern flounder remain in these creeks until they attain a length of about 20.3-25.4 cm (8-10 inches), at which time they disperse into other available estuarine habitats. They can even tolerate fresh water and have been taken by electrofishing.
Southern flounder are ambush predators with the ability to change coloration so that they blend in with the substrate. They are frequently found in shallow water near oyster reefs or the mouths of small rivulets draining the high marsh as the tide ebbs. Food items include grass shrimp, mummichogs, spot, and striped and white mullet. These prey animals are commonly associated with edge habitats in the estuary such as the edges of oyster bars and along salt marshes. Southern flounder are widely distributed in the ACE Basin and frequently co-occur with red drum.
Southern flounder are popular in both the commercial and sport industries in the Southeast and Gulf of Mexico. In the latter, much of the commercial catch of southern flounder results from bycatch from the shrimp fishery. Recreationally, southern flounder are caught by nighttime gigging in tidal creeks and marshes, as well as by hook and line
Fernandez, E. 1991. The juvenile life history of the southern flounder (Paralichthys lethostigma) in South Carolina. M.S. Thesis. University of Charleston, Charleston, SC.
Murdy, E.O., R.S. Birdsong, and J.A. Musick. 1997. Fishes of the Chesapeake Bay. Smithsonian Institution Press, Washington, DC.
Reagan, R.E., Jr. 1985. Species profiles: Life histories and environmental requirements of coastal fishes and invertebrates (Gulf of Mexico)--Southern Flounder. U.S. Department of Interior, Fish and Wildlife Service, Biological Report 82(11.30). U.S. Army Corps of Engineers, Report TR EL-82-4. Washington, DC.
Wenner, C. 1998. Personal communication. South Carolina Department of Natural Resources, Charleston, SC.