||Paralichthys lethostigma Jordan and Gilbert, 1884
Doormat and halibut
Other Taxonomic Groupings
P. lethostigma is one member of a large family of distinctive benthic flatfishes that inhabit continental shore waters in the tropical and temperate
zones of the Atlantic, Pacific and Indian oceans. Flatfishes such as the flounders are unlike most other fishes in that they begin life as bilateral animals, having equal right and left sides, and swim as do other fishes.
However, toward the end of the larval period, flatfishes settle to the benthos and take up a cryptic, somewhat sedentary lifestyle, lying on one side of the
body, and swimming laterally to the substratum. Metamorphosis to the juvenile
stage involves complex modification of the skeletal structure of the head, and
rearrangement of the nervous system and muscle tissues. Additionally, the eye on
the side which faces the substratum (termed the blind-side eye) begins to
migrate to the upper side of the body. P. lethostigma is a left-eye
flounder, thus it lies on its right side, and at metamorphosis, the right eye
migrates to the left side of the head. Lefteye flounders sometimes exhibit
sexual dimorphism, with females having eyes that are closer together than in
males, and males having somewhat longer pectoral fins (Rogers and Van Den Avyle
Body color is light to dark brown with diffuse non-ocellated dark spots and
blotches. The blindside is white or dusky. P. lethostigma are
characterized by the following meristic (number of structures per body part)
|Dorsal fin Rays:
|Pectoral Fin Rays:
|Upper Gill Rakers:
||2-3 (Upper Limb)
|Lower Gill Rakers:
||8-11 (Lower Limb)
|Lateral Line Scales:
Potentially Misidentified Species
Paralichthys lethostigma is sometimes
confused with P. albigutta, the gulf flounder. The two are easily
distinguished based on the much smaller size of the gulf flounder, which grows
only to 15 inches (38 cm). Additionally, the gulf flounder has 3 ocellated
spots: 2 vertically placed posterior to the pectoral fins, and 1 placed inside
the base of the tail.
HABITAT AND DISTRIBUTION
The southern flounder, Paralichthys lethostigma, occurs from North
Carolina south through Florida and the Gulf of Mexico to Texas.
The southern flounder occurs throughout the Indian River Lagoon.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Southern flounder attain a size of up to 3
feet (91 cm) in length, and can weigh as much as 9 kg (24.1 lbs.) (Smith et
al. 1999). The von Bertalanffy growth model predicts a maximum age for summer
flounder of approximately of 20 years (Reagan and Wingo 1985).
P. lethostigma is one of the largest
and most commercially valuable flounders in the western North Atlantic (Burke
et al. 1991).
Adults migrate to offshore spawning grounds
during late fall and winter, though some remain in estuaries year-round.
Spawning migrations are usually preceded by a drop in water temperature of
4 - 5 °C. Males move
seaward earlier than females, with few remaining in estuaries after November
(Reagan and Wingo 1985). In North Carolina, southern flounders begin migration
in the fall; in Texas, they migrate from October through December (Reagan and
Laboratory experiments from Texas indicate that
approximately 3 weeks before spawning takes place, male southern flounder
begin following gravid females. In tank experiments, the first spawning was in
December and occurred at midday. Females swam to the surface and released eggs
that were immediately fertilized by attending males. Fertilization was 30% to
50% successful, and 6% to 35% of the eggs hatched within 61 - 76 hr (Reagan
and Wingo 1985).
Females become sexually mature at 2 years of age in
Texas, while the youngest mature female southern flounder in northern Florida
was 4 years old (Reagan and Wingo 1985).
Thirteen southern flounders examined in the
laboratory, produced a total of 120,000 eggs (approximately 9,230 eggs per
female) (Reagan and Wingo 1985).
Eggs of P. lethostigma range from 0.85
- 0.95 mm in diameter (Powell and Henley 1995), with a single oil globule.
Laboratory rearing of southern flounder shows that eggs hatch after 3 days at
18°C and 30‰ salinity (Denson and
Smith 1997). Larvae begin to feed when 4 -6 days old, and show signs of
becoming premetamorphic by day 14. By day 16, larvae begin to settle out of
the water column and congregate on the bottom. By day 21, larvae show signs of
adult pigmentation, and begin to rest on their left sides, though their eyes
remain in position. By day 23, metamorphosis is initiated and the left eye
begins to migrate to the right side. Most animals had completed metamorphosis
by day 36 (Denson and Smith 1997). In culture experiments, yolk-sac larvae
began metamorphosing to postlarvae at 40 - 46 days, when they were
approximately 8 - 11 mm in length. Metamorphosis to the
juvenile stage was complete by 50 - 51 days (Reagan and Wingo 1985). Data from
Powell and Henley (1995) show that larvae complete metamorphosis when they
reach approximately 8.7 - 9.0 mm SL. By this time, the migrating eye has
reached the dorsal midline, and the larval stage is complete.
Powell and Henley (1995) examined egg and larval
development in both P. lethostigma and P. albigutta. Results
from their study show that fins begin to develop when larvae reach
approximately 5.4 mm notochord length (NL). The dorsal fin is generally the
first to begin development, followed by the caudal, anal, pelvic, and pectoral
fins (Powell and Henley 1995). Development of the caudal fin in P.
lethostigma can begin when larvae are approximately 5.5 mm NL, but fin
rays are not observed until larvae attain 8.2 mm SL. Dorsal fins begin to
develop when larvae are in the preflexion stage, at approximately 6.5 mm NL.
The dorsal fin is first observed in the head region, with development
proceeding posteriorly. By the time larvae reach 8.4 mm standard length (SL)
the dorsal fin is fully developed. Following postflexion, when larvae reach
approximately 7.3 mm standard length (SL), anal fin rays begin to develop,
with the full adult complement of fin rays reached at a body size of 8.4 mm
SL. Pelvic fins are first observed on larvae at approximately 8.2 mm SL, and
are fully developed by the time larvae attain 9.7 mm SL. Pectoral fins first
begin formation when larvae are approximately 8.4 mm SL, and are fully formed
when larvae exceed 11.0 mm SL.
Pigmentation is first observed in middle-stage eggs,
following blastopore closure. In larvae, pigmentation is more pronounced in
the caudal area, being less developed overall in P. lethostigma than in
its close relative P. albigutta, the gulf flounder (Powell and Henley
Larvae spawned offshore in the Atlantic Ocean make
their return to estuarine habitats by passive transport on nearshore and tidal
currents from November through April, with a peak in recruitment occurring in
February (Burke et al. 1991). In the gulf of Mexico, Southern flounder
postlarvae are caught along the Gulf of Mexico coast during winter and early
spring. At Galveston Island, Texas, southern flounder postlarvae
18 - 34 mm in total length (TL) were captured during February,
March, and May. Fish 25 - 51 mm TL were caught in the Mississippi River during
the spring. In Aransas Bay, Texas, the peak movement of postlarvae flounders
into estuaries is in February, when water temperature is 16.0 - 16.2 °C (Stokes 1977).
Temperature influences the migration of
postlarval and adult southern flounders (Reagan and Wingo 1985). In Louisiana
coastal waters, adult southern flounders have been collected at temperatures
ranging from 5 - 35 °C.
Southern flounder are highly euryhaline,
and withstand fluctuations in salinities ranging from 0- 35‰ or more. Data
from Smith et al. (1999) indicates that salinity tolerance in this species
increases with age.
Adult P. lethostigma make extensive migrations
from estuarine habitats in order to spawn in offshore waters. Eggs of P.
lethostigma are buoyant at 32 ‰, and sink at 29‰, though data indicate
that eggs that sink may still hatch. Experiments conducted by Smith et al.
(1999) showed that eggs incubated in water with a salinity between 0-5 ‰ all
died within a day. Eggs incubated at 10 ‰ had greater hatching success
(82%), but all larvae moved sluggishly and died shortly after hatching. Eggs
incubated in water of salinities between 15 - 35 ‰ were normal in appearance
and were active. However, larvae reared through metamorphosis to the juvenile
stage showed greater mortality at 15‰ salinity than at either 25‰ or 35‰.
Further, recently metamorphosed juveniles showed less tolerance to freshwater
conditions than did older fish (Smith et al. 1999).
Southern flounder eggs and larvae from wild
populations develop in offshore waters, with late stage, premetamorphic larvae
(stage 4b - 5), likely returned to estuarine habitats via passive transport on
nearshore and tidal currents. Once returned to estuaries, larvae settle on the
substratum and metamorphose into juveniles. In one North Carolina study,
comparative data from Burke et al. (1991) suggests that settlement in P.
lethostigma is influenced by salinity. These authors reported that though
larvae of both summer and southern flounder begin to recruit into estuaries
during February, southern flounder larvae concentrated on tidal flats near the
heads of estuaries where salinity ranged from 9 - 25‰, and the substratum
had a low sand content (4 - 50%). Conversely, summer flounder larvae settled
more downstream, in the middle reaches of estuaries where salinity ranged from
24 - 35‰ and the substratum had a much higher sand content (53 - 95 %).
Burke et al. (1991) also reported that juvenile
southern flounder moved further upstream to more riverine environments later
in the spring, while juvenile summer flounder tended to remain in higher
salinity tidal areas near Spartina saltmarshes. Catch comparisons
showed that approximately equal numbers of southern flounder were caught in
sandy versus muddy substrate types in low salinity waters; while summer
flounder were most abundant in sandy substrata in higher salinity waters.
Burke et al. (1991) concluded that southern flounder settlement is more highly
correlated with salinity, while summer flounder settlement is more highly
correlated with substratum type.
Other Physical Tolerances
P. lethostigma tolerates low dissolved oxygen concentrations (less than 5 mg/l). However, in a laboratory study, postlarval southern flounder attempted avoidance when dissolved
oxygen concentrations in culture vessels fell
below 3.7 mg/l (Reagan and Wingo 1985).
Southern flounder are carnivorous fishes that
are generally considered to be top or near-top predators. Larvae reared under
laboratory conditions begin feeding on rotifers 4 - 6 days posthatch. By 8 -
13 days posthatch, larvae begin to feed on newly hatched Artemia
nauplii (Denson and Smith 1997).
Small southern flounders consume a wide variety of
invertebrate prey, but upon reaching approximately 20 mm total length (TL),
they become primarily piscivorous (Reagan and Wingo 1985). Based on
differences in morphology and behavior between summer flounder and southern
flounder in North Carolina, Burke (1995) compared prey distribution and
feeding ecology between the 2 species following metamorphosis to the juvenile
stage. Southern flounder juveniles have generally larger mouths, larger,
inwardly curved teeth, and fewer, heavier gill rakers than do summer flounder.
They also tend to remain still on the bottom, waiting for prey to come within
striking distance (Minello et al. 1987; Burke 1995). Small southern flounder
primarily consumed amphipods and mysid shrimp, followed by copepods, insects,
fish and invertebrate parts. In this study, summer flounder 20 - 60 mm SL
consumed spionid polychaete worms, followed by clam siphons, mysid shrimp,
calanoid copepods, the blue crab, Callinectes sapidus, and small
fishes. From this data, Burke (1995) concluded that post-settlement
differences in feeding habits developed between the 2 species, with southern
flounder shifting to more mobile prey which could be attacked from below, and
summer flounder continuing to feed upon benthic prey organisms.
The adult diet of P. lethostigma consists
primarily of fish, but is augmented by crustaceans depending upon regional
location. In Louisiana, adult southern flounders eat shrimp and fish; though,
Fox and White (1969) reported that the primary prey species for southern
flounder was striped mullet (Mugil cephalus). Also included in the diet
are fat sleepers (Dormitator maculatus) and anchovies (Anchoa spp.).
Larger flounders (150 mm long) ate primarily anchovies, menhaden (Brevoortia
spp.), sciaenids, and mullet (Reagan and Wingo 1985).
Adult P. lethostigma spend the warmer
months in coastal embayments and riverine habitats in the upper reaches of
estuaries (Rogers and Van Den Avyle 1983). Many adults migrate to offshore
spawning grounds during late fall and winter, though some do remain in
estuaries year-round. Larvae spawned offshore make their return to estuarine
habitats by passive transport on nearshore and tidal currents. In a study
conducted in North Carolina, Burke et al. (1991) reported that peak
recruitment into estuaries by late stage (stage 4b and 5), premetamorphic
larvae occurred in February, though larvae were collected from late November
through mid-April. These larvae settled into tidal mudflats near the head of
the estuary, however, in spring, southern flounder apparently migrated
upstream into riverine habitats. Spring through summer, southern flounder
prefer the silt and mud substrata of coastal bays and river systems, and
become most common in the upper reaches of estuaries, sometimes entering
freshwater (Burke et al. 1991; Smith et al. 1999).
In a comparative study, Burke et al. (1991) reported
that larvae of both southern and summer flounder recruit into estuaries during
the same period, and for a time, show considerable overlap in distribution
within an estuary. However, segregation occurs quickly (Burke et al. 1991;
Burke 1995). Premetamorphic larvae of southern flounder tend to concentrate on
tidal flats in the upper reaches of estuaries where salinity ranges from 9 -
25‰, and the substratum consists of 4 - 45 % sand. Conversely,
premetamorphic larvae from summer flounder generally move into silt and
mudflat areas in the lower and middle reaches of estuaries where salinity
ranges from 24 - 35‰ and the substratum consists of 50 - 95 % sand (Burke
et al. 1991). Capture data following segregation of the 2 species within the
Newport River Estuary, North Carolina, showed that summer flounder were most
common on sand flats than on mudflats in the lower estuary, while there was
little difference in capture rates among southern flounder in sandy vs. muddy
substrates in the upper reaches of the estuary. Burke et al. (1991) concluded
that settlement in P. dentatus is most likely influenced by substratum
type, while that of P. lethostigma is influenced by salinity.
A tank study showed that southern flounder
tend to be more active at night than during the day (Reagan and Wingo 1985).
The southern flounder is a valuable sport and
commercial fish along the Gulf coast of the United States. Most of the commercial catch in the Gulf
of Mexico is incidental to the catch by shrimp trawlers. There has been
significant interest in utilizing southern flounder as an aquaculture species.
Studies in the southeastern U.S. and in the Gulf of Mexico are currently
underway to improve spawning techniques and develop larval rearing methods for
southern flounder in order to improve its attractiveness as an aquaculture
product (Jenkins and Smith 1999; Smith et al. 1999).
Flounders of all species are harvested annually from
waters in and around the Indian River Lagoon, and are especially prized by recreational
anglers. However, the commercial fishery is not of particularly high value.
For the years 1987 - 2001, 1.7 million pounds of flounders were harvested, with
a dollar value of over $3.1 million reported in the 5 county area encompassing
the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin Counties).
This ranks flounders nineteenth in commercial value within the IRL, and
twenty-ninth in pounds harvested.
Figure 1 below shows the dollar value of the flounder
fishery to IRL counties by year. Note that all species of flounders were
combined in the data presented. As shown, commercial catch ranged from a low of $77,149 in
1987 to a high of over $350,927 in 1999. Volusia County annually accounts
for the largest percentage of the flounder catch with 83% in total (Figure 2),
followed distantly by Brevard County, which accounts for 8% of the total.
Indian River, St. Lucie and Martin Counties account for 3%, 4% and 2% of the
total respectively. Note that the fishery's value brings in $125,000 -
$300,000 annually to Volusia County businesses, while in all other IRL counties,
the dollar value is typically less than $25,000.
Figure 1. Annual dollar value of the commercial catch of flounders to the 5-county area of the Indian River Lagoon.
Figure 2. Breakdown of total flounder dollar value by county for the years 1987 - 2001.
Table 1. Total dollar value of flounders to IRL counties between 1987 -2001.
||Value to IRL
Table 2. By-county annual and cumulative percentages of the flounder harvest for the years 1987-2001.
Table 3. By county cumulative dollar value and percentage of total for the IRL flounders harvested from 1987 - 2001.
flounder fishery in Florida accounts for 65 - 70% of the annual state-wide
harvest (Florida Fish and Wildlife Conservation Commission 2004). Landings on
the Gulf coast of Florida are somewhat lower than those on the East coast,
averaging approximately 198,015 pounds per year. On the Atlantic coast,
landings have averaged less than 300,000 pounds per year since 2001.
However, catch rates on both coasts are apparently stable, and have remained so
since the early 1990s.
Southern flounder are recreationally important in the
Indian River Lagoon on a seasonal basis, specifically during the late fall and
winter when large specimens may be landed as they migrate out of the lagoon for
spawning. This species was first regulated by the State of Florida in
1996, when a 10-fish bag limit and 12-inch minimum size limit was implemented.
Since 1997, the recreational
harvest in the 5-county area encompassing the Indian River Lagoon has remained
fairly consistent, with 1.3 million fishes harvested, an average of 166,500 per
year taken by recreational anglers between 1997 - 2001. The lowest harvest
was recorded in 2004, when 133,643 southern flounder were captured. The
highest harvest occurred in 1999 when 201,195 southern flounder were taken.
Approximately 45.8% of the catch was taken
in inland waters other than the Indian River Lagoon. Within the IRL,
anglers caught 379,472 southern flounder, 28.5% of the total. Coastal waters from the shoreline to 3 miles offshore
accounted for 23.2%, while offshore waters to 200 miles accounted for only 2.4%.
Figure 3. Survey data for the southern flounder recreational fishery showing the number of fishes harvested in East Florida waters from 1997 - 2004.
Figure 4. Summary of the southern flounder recreational harvest and percentage of total by area from 1997 - 2004.
Table 4. Summary data for the southern flounder, Paralichthys lethostigma, recreational fishery in Eastern Florida waters from 1997 - 2004. Data provided by National Marine Fisheries Service, Fisheries Statistics Division, NOAA.
||To 200 Miles
||To 3 Miles
Table 5. By-county annual and cumulative percentages of the southern flounder harvest for the years 1997 - 2001. Data provided by National Marine Fisheries Service, Fisheries Statistics Division, NOAA.
||To 3 Miles
||To 200 Miles
Table 6. Summary of the southern flounder recreational harvest and percentage of total fish captured in each area from 1997 - 2004. Data provided by National Marine Fisheries Service, Fisheries Statistics Division, NOAA.
||To 3 Miles
||To 200 Miles
Burke JS. 1995. Role of feeding and prey distribution of summer and southern flounder in selection of estuarine nursery habitats. J Fish Biol 47: 355-366.
Burke JS, Miller JM, Hoss DE. 1991. Immigration and settlement pattern of Paralichthys dentatus and P. lethostigma in an estuarine nursery ground, North Carolina, USA. Netherlands J Sea Res 27: 393-405.
Denson MR, Smith TI. 1997. Diet and light intensity effects on survival, growth and pigmentation of southern flounder Paralichthys lethostigma. J World Aquacult Soc 28: 366-373.
Florida Fish and Wildlife Conservation Commission. Recreational fisheries landings. Available online: http://myfwc.com/research/saltwater/fishstats/recreational-fisheries/landings. Accessed: 4 July 2016.
Fox LS, White CJ. 1969. Feeding habits of the southern flounder, Paralichthys lethostigma. Barataria Bay, Louisiana. Proc La Acad Sci 32: 31-38.
Jenkins WE, Smith TI. 1999. Pond nursery production of southern flounder (Paralichthys lethostigma) and weaning to commercial diets. Aquaculture 176: 173-180.
Minello TJ, Zimmerman RJ, Klima EF. 1987. Creation of fishery habitat in estuaries. In: Beneficial uses of dredged material: proceedings of the first interagency workshop, 7-9 October 1986, Pensacola, Florida. Final Report. 106-120.
Powell AB, Henley T. 1995. Egg and larval development of laboratory-reared gulf flounder, Paralichthys albigutta, and southern flounder, P. lethostigma (Pisces, Paralichthyidae). Fish Bull 93: 504-515.
Reagan Jr RE, Wingo WM. 1985. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (Gulf of Mexico) - southern flounder (Paralichthys lethostigma) (No. NP-5901733). Mississippi State Univ., Mississippi State (USA). Dept of Wildlife and Fisheries.
Rogers SG, Van Den Avyle MJ. 1983. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (South Atlantic). Atlantic Menhaden (No. FWS/OBS-82/11.11). Georgia Univ., Athens (USA). School of Forest Resources.
Smith TI, Denson MR, Heyward LD, Jenkins WE, Carter LM. 1999. Salinity effects on early life stages of southern flounder Paralichthys lethostigma. J World Aquacult Soc 30: 236-244.
Stokes GM. 1977. Life history studies of southern flounder (Paralichthys lethostigma) and Gulf flounder (P. albigutta) in the Aransas Bay area of Texas. Texas Parks and Wildlife Dept Technical Series 25. 37 p.
Report by: K. Hill, Smithsonian Marine Station
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Page last updated: July 9, 2005