Flounder

Flounder is a common name for numerous flatfish species in several families, including Pleuronectidae and Paralichthyidae, with the summer flounder serving as a widely recognized representative. Flatfish undergo a striking developmental transformation, hatching with a symmetrical body and one eye on each side like typical fish, then migrating one eye to the other side as they mature and settle to a life lying on the seafloor. Flounders inhabit coastal sandy and muddy bottoms in temperate and tropical seas worldwide, where their mottled coloration provides excellent camouflage against predators and prey alike. Many flounder species are important components of coastal and estuarine ecosystems, and some support significant recreational fisheries.

Key identification features for flounder:

• Flattened, oval body with both eyes positioned on one (upper) side of the head
• Mottled brown, grey, or olive coloration on the eyed side, capable of subtle color matching to substrate
• Plain white or pale coloration on the blind (bottom) underside
• Long dorsal and anal fins running along most of the body's edge
• Eye placement (left-eyed vs right-eyed) helps distinguish between families and species

Size varies by species, with many common flounders reaching roughly 30-60 cm. Flounders are distinguished from soles by a larger mouth and more pointed head shape.

Flounders are demersal fish found lying on or partially buried in sandy, muddy, or mixed sediment seafloors in coastal marine and estuarine waters of temperate and tropical regions worldwide. Most species inhabit relatively shallow depths, from the intertidal zone down to around 100-200 m, with some species found deeper on the continental shelf. Many flounders use estuaries, bays, and river mouths as nursery habitat during their juvenile stages before moving to deeper offshore waters as adults. They favor areas with soft substrate suitable for burying themselves partially to avoid detection.

Flounders are ambush predators that lie still, often partially buried in sediment, waiting for small fish, shrimp, and other invertebrates to pass within striking range before lunging upward to capture prey. They are capable of rapid color and pattern adjustments to blend with the surrounding substrate. Most flounder species undergo seasonal migrations, moving between shallow inshore nursery habitats and deeper offshore spawning grounds. Spawning typically occurs offshore, with females releasing large numbers of pelagic eggs that drift and hatch into free-swimming, bilaterally symmetrical larvae before undergoing metamorphosis and settling to the bottom. As bottom-dwelling predators, flounders help regulate populations of small benthic and demersal prey species.