Flounder are flatfish known for their distinctive flattened bodies. They inhabit various aquatic environments, and understanding their habitat provides insight into their biology and behavior.
Flounder Habitat Explained
Flounder are primarily saltwater fish, found in marine and estuarine environments. Most species reside on or near the seabed, often burrowing into soft substrates like sand or mud. Their habitats extend from shallow coastal waters and estuaries to the deeper continental shelf, with some species found at depths exceeding 100 meters.
Estuaries, where freshwater rivers meet the sea, are important habitats for many flounder species, especially during their juvenile stages. These brackish environments offer a mix of salinities, and flounder tolerate varying salt concentrations. For instance, Summer Flounder inhabit shallow coastal or estuarine waters, migrating offshore to deeper, colder waters during cooler months. Winter Flounder also utilize inshore bays and estuaries for spawning, preferring muddy, sandy, or pebbly bottoms.
While most flounder are marine, some species, like the European Flounder (Platichthys flesus), exhibit adaptability, tolerating a wide range of salinities and even moving into freshwater rivers for part of their life cycle. Southern Flounder can also move between freshwater and saltwater environments. This adaptability allows them to exploit diverse feeding grounds and nursery areas.
Diversity Among Flounder Species
The term “flounder” encompasses a diverse group of flatfish species belonging to the order Pleuronectiformes. This order includes families like Bothidae (left-eyed flounders) and Pleuronectidae (right-eyed flounders). The distinction refers to which side of their body both eyes migrate to during development.
Well-known examples illustrate this diversity. Summer Flounder (Paralichthys dentatus), also known as fluke, are left-eyed flatfish, with their eyes on the left side of their head. They are common along the Atlantic coast of North America, from Nova Scotia to Florida.
In contrast, Winter Flounder (Pseudopleuronectes americanus) are right-eyed flatfish, with both eyes positioned on the right side. They are prevalent in the Northwest Atlantic, ranging from Canada to North Carolina. The European Flounder (Platichthys flesus) is native to coastal waters of Europe and is right-eyed.
Remarkable Adaptations of Flounder
Flounder possess adaptations for their bottom-dwelling habitats. Their most striking feature is their flattened, disk-shaped body, which allows them to lie inconspicuously on the seafloor. When flounder larvae hatch, they resemble typical fish with an eye on each side of their head. During metamorphosis, one eye migrates to the other side of the head, resulting in both eyes being on the upward-facing side of their flattened body in adulthood. This eye migration provides them with a wide field of vision as they lie flat.
Flounder can rapidly change their skin coloration and patterning to match the surrounding substrate. This ability is due to specialized pigment cells in their skin, allowing them to blend with sand, mud, gravel, or even checkerboard patterns. This cryptic coloration helps them ambush prey and evade predators such as sharks and eels. Their bottom-dwelling behavior, combined with their camouflage, allows them to remain hidden and strike with sudden speed, making them effective ambush predators in their diverse environments.