December Fish(es) of the Month: Gulf Flounder Paralichthys albigutta and Southern Flounder Paralichthys lethostigma

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December Fish(es) of the Month: Gulf Flounder Paralichthys albigutta and Southern Flounder Paralichthys lethostigma

Dr. Geoffrey Smith

NWFSC Biology Instructor

December 1st marks the reopening of harvest for these two species in Florida’s waters. The Gulf and Southern Flounder are very similar in appearance and life history characteristics, hence their management as a single species for recreational fishing harvest in most states where they co-occur.

Both species range in color from nearly white to tan to dark brown based on both water clarity/color and substrate (bottom sediment) coloration. Gulf Flounder can be recognized by their three ocellated (surrounded by a ring) spots that form a large triangle on the side of their body (Figs. 1 and 2). These spots can sometimes be difficult to make out on fish that are very uniform in their body coloration. Southern Flounder do not have any ocellated spots but have numerous small dark and light spots all along their side (Figs. 1 and 2).

Like all flounders, adult Gulf and Southern Flounder lay on the bottom of the sea floor most of the time. However, unlike sting rays and skates that are dorso-ventrally compressed (narrow top to bottom) and have the bottom of their bodies sitting on the sea floor, the flounders are laterally compressed (narrow side to side) and lay on the sea floor with one side of their body. Both of their eyes are on the opposite side of the body facing upward. This is not how flounders start out though. Recently hatched flounder swim upright like most fish and have an eye on each side of their body, but as they grow, one eye moves to the opposite side of the body before the flounder starts laying on the bottom. Flounder are classified as being either right- or left-eyed based on which side the eyes end up on in adults if you were to stand the fish upright, this is called the eyed side. The side that lays on the bottom and has no eyes is called the blind side, and this side is typically all white in coloration. Both the Gulf and Southern Flounders are left-eyed, but on very rare occasions there will be a right-eyed individual.

It is thought that both of these species spawn in offshore waters after adults migrate in large numbers from estuaries to ocean waters in the fall. The larvae are transported to inshore estuary waters where they reside until reaching maturity and migrating offshore. After migrating offshore for the first time, males of both species often remain there for the rest of their lives and typically only reach about 12 inches in length. Females on the other hand, generally migrate back inshore after spawning and reach considerably larger sizes (exceeding 25 inches on occasion). Both species are relatively short-lived with maximum ages ranging from 4-11 years depending on species and sex.

Both the Gulf and Southern Flounders are popular sportfish in the southeastern US. They are targeted during the day with traditional hook and line tackle in tidal creeks, channel edges, and around structure such as oyster reefs and dock pilings. At night, they will often move into shallow waters near the shore to feed where they are targeted with lights and gigs. Flounder regulations in Florida were recently updated (March 2021), largely due to evidence of decreased numbers and overfishing, particularly on the east coast of Florida. The new regulations include an increase in minimum size (from 12” to 14” total length), decrease in bag limit (from 10/person to 5/person), and a closed season of October 15 – November 30. Current flounder regulations for Florida can be found at https://myfwc.com/fishing/saltwater/recreational/flounder/.

Fig. 1: Gulf Flounder (left) with its three distinct ocellated spots and Southern Flounder (right) with a lack of any ocellated spots. Photo credits: J. Van Tassell and D. Robertson hosted on https://biogeodb.stri.si.edu/caribbean/en/pages (Gulf Flounder); https://ncfishes.com/ (Southern Flounder).

Fig. 2: Comparison of three common flounder species with ocellated spots (or lack of) highlighted. The upper left fish is a Gulf Flounder with its three ocellated spots forming a tringle. The upper right fish is a Summer Flounder, which has 5 ocellated spots in an hourglass pattern. This species is found along the east coast of Florida, but is not found in the Gulf of Mexico. The fish on the bottom is a Southern Flounder, which lacks any ocellated spots. Photo credit: North Carolina Sea Grant.

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