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

Dr. Geoffrey Smith

NWFSC Biology Instructor

December 1^st marked 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.

The genus name Paralichthys is derived from the Greek para, meaning beside or parallel, and the Greek ichthys, meaning fish. Put together, this roughly translates to “beside fish” or “parallel fish,” referring to the fact that most flounder, like these fish, lie on the bottom on their sides. The species names for both are in reference to their overall appearance.

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. Their species name albigutta is derived from the Latin albus, meaning white, and gutta, meaning spot, in reference to the Gulf flounder’s generally light coloration with prominent dark spots. Southern Flounder do not have any ocellated spots but have numerous small dark and light spots all along their side (Figs. 1 and 2). Their species name lethostigma is derived from the Latin lehto, meaning death or forget, and the Greek stigma, meaning spot, essentially translating to “death of spots” or “forgotten spots” in reference to not having any large spots like the Gulf Flounder and a number of other related species.

Like all flounders, adult Gulf and Southern Flounder lie 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 lie 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 lying on the bottom. Flounders are classified as being either right-eyed 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 lies 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 structures 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), a 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 myfwc.com/flounder.