Info > Southern Flounder
common fish is found Gulfwide, on mud, and to a lesser degree,
sand bottoms, from shallow, low-salinity estuaries to nearshore
and shallow offshore waters. Southern flounders commonly enter
fresh water and have been found 100 miles up rivers.
body is very compressed laterally and right side is white
and eyeless. The left side has both eyes and is olive brown
in color with dark and white spots. Flounders, like other
fish, hatch with one eye on each side of their head. Movement
of the right eye to the left side of the head begins when
the fish is a to ½ inch in length and is complete when
the fish is ¾ inch to 1 inch in length. At this same
time, the left side develops its dark color and the right
side turns white.
Male and female southern flounder are almost like two different
species of fish. Males grow slower and have a short life span,
almost never living over 3 years old or growing over 14 inches
long. Females live longer and can grow to 28 inches. Also,
after their first year of life, males live mostly in offshore
waters. This means that most of the inshore catch consists
of females. Southern flounder, both male and female, spend
their first year after hatching in shallow, low-salinity estuary
and even river waters. As they grow, they tend to use slightly
deeper waters, but still within inshore estuaries. As temperatures
cool in the fall, mature southern flounders move to the lower
portions of the estuaries near the Gulf of Mexico, where they
stage in large numbers. Between mid-October and mid-November
they begin a mass migration into Gulf offshore waters to spawn.
This migration can be slow if water temperatures cool gradually,
or it can happen all at once with the passage of a strong
cold front. Between this period and February/March, very few
large southern flounders are found inshore. Once offshore,
spawning activities take place between November and January,
with a peak in December. During the two months each female
spawns, they will spawn every 3 to 7 days, producing an average
of 44,225 to 62,473 eggs per spawn. After spawning, the females
move back into the estuaries between January and April to
start the cycle over again. The seasonal spawning movement
cycle is the key to understanding southern flounder biology.
Tagging studies in several southeastern states indicate that
between spawning migrations, southern flounders move only
short distances, usually within the same bay system. The spawning
migration, however, reshuffles the deck and some fish move
considerable distances. A Georgia study showed maximum movement
of 334 miles. South Carolina research showed 243 miles. One
North Carolina study had a southern flounder move 257 miles
and another 444 miles. In the last study, a fish moved 387
miles in 131 days, which is an average of 3 miles a day.
Southern flounder are well adapted for ambushing quick-moving
prey such as fish or shrimp. Their flattened shape allows
them to become nearly invisible on the bottom. Their brain
has large optic lobes to serve their large eyes, and they
have large mouths and strong teeth. Typically, they remain
motionless on the bottom and wait for their prey to come within
striking distance before attacking. While waiting, flounder
show rapid eye movements as they track their prey. Research
indicates that flounders will eat from 4 to 8 percent of their
body weight in food each day. Feeding activity is heaviest
at water temperatures of 61 to 77º F and during the 3-day period
following a first quarter moon and the 3-day period before
a new moon.
Southern flounders eat a wide variety of food items, including
shrimp, mullet, anchovies, croakers, and menhaden (pogies).
One research project in Texas reported southern flounders
to be the dominant fish predator on brown shrimp during the
spring in Galveston Bay. The researcher also noted an increase
in the predation rate on brown shrimp in muddy water. This
may have been due to murky water giving the flounder a feeding
advantage or to a change in shrimp behavior. When southern
flounder feed on fish, they seem to prefer smaller fish. Unlike
most predatory fish which eat larger fish as they get larger,
flounder just eat higher numbers of small fish.
Up to 3 feet in length and 20 pounds, but most fish caught
are 1-5 pounds.
very lean, white flesh.
Facts (fact sheet)
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