Natural History Notes of the Southern Flounder (Paralichthys lethostigma)—Elusive Inshore Catch
By: Marlee Hayes
Note: Both the Southern & Gulf Flounder are caught in the Gulf of Mexico. This article will focus mainly on the southern flounder.
The flounder may be the most elusive of the inshore slam fishes, with an unclaimed 3rd place prize at our most recent tournament, the 11th Annual Five Rivers Tournament. Flounders, along with other flatfish (halibuts, soles, and tonguefish) belong in the order Pleuronectiformes, which is group of fishes with extremely compressed bodies. The Southern Flounder is a member of the Bothidae family, or the left eye flounders, meaning both eyes will appear on the left side of the body after larval development. For flounder, at hatching, the eyes are present on both sides of the head and one will later migrate to other side. Interestingly, rare cases have been documented within Bothidae where eyes are on the right side of the body. The southern flounder (one of the species in the Gulf) is pale to dark brown and may have diffuse/patchy spots varying from pale to dark in coloration on the upper (eye side) of the body. The spots may seem to form lines along the body and oscillating spots are not present. Large adults may lack spots and look one overall color dorsally, with a light white to dusky underside . The lateral line arches over the pectoral fin and upper jaw extends past the eye. They may reach lengths of 3 feet.
The southern flounder is found from North Carolina to Florida, and the Gulf of Mexico to Texas. They inhabit estuaries and coastal areas over soft bottoms (up to 140 feet depth). Adults have been reported to enter rivers. Young are found in shallow areas and may be found in low salinity areas. During fall/winter adults migrate away from the bays and into the open Gulf to breed. Males and females are sexually dimorphic (external differences in males and females), with males having greater distance between the eyes and longer pectoral fins and front dorsal rays. Additionally females reach larger sizes at maturity, up to 25 inches while males rarely exceed 12 inches . Like other flounder, this species will rest along the bottom, eye side up. Their small body cavity and lack of swim bladder allow flounders to rest along the bottom. Southern flounder are able to camouflage themselves to the surrounding bottom extremely well. Chromatophores in their skin can be aggregated together or dispersed, effectively allowing the flounder to adjust to match its surroundings. This is same process that allows cephalopods (squids, octopi, and their relatives) to change colors or flash fluorescent colors. This ability combined with their flat shape make the flounder, an ambush predator, nearly invisible on the ocean floor, as it waits from some unsuspecting fish or crustacean to wonder by . Flounder can consume up to eight percent of their body weight daily with a large portion of that consisting of fish . Interestingly, it seems as flounder get larger they do not consume larger fish relative to their own body size, instead they just consume more small fish of a similar size that they consumed as smaller adults .
Southern flounder are popular in both commercial and recreation fisheries. These flounder have been coined the mud flounder, based on their preference for muddy/sandy bottoms. Larger flounder are nicknamed “doormats” . Flounder can be caught on hook and line and by gigging . Artificial lures and live bait have proven successful methods when fishing via rod and reel with light tackle. Flounder are more often caught with live bait, when compared to dead; minnows and shrimps pulled slowly along bottom are often an efficient method. In heavily vegetated areas, shallow-running spoons work well .
Flounder are very popular fish food prepared whole or fileted with dishes consisting of fried, baked, broiled, sautéed, stuffed, and raw, as sashimi, varieties. Both the southern and Gulf flounder appear relatively stable from a conservation perspective. Research for further developing flounder aquaculture is underway in some states  . It would seem flounders, despite their popularity in the fisheries, will continue to be a sportsman’s favorite for years to come with well managed regulations.
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- Texas Parks and Wildlife. Southern Flounder (Paralichthys lethostigma). https://tpwd.texas.gov/huntwild/wild/species/flounder/
- The University of Southern Mississippi Gulf Coast Research Laboratory. 2017. Southern Flounder and Gulf Flounder. http://gcrl.usm.edu/public/fish/flounder.php