Flounder are saltwater fish. These diverse flatfish are found globally in marine environments. This article explores their typical habitats, the biological adaptations that allow them to thrive in salty waters, and the variety of species within this intriguing group.
Flounder’s Aquatic Home
Flounder are demersal fish, meaning they spend their lives on or near the bottom of bodies of water. They primarily inhabit a variety of marine settings, including shallow coastal waters, estuaries, and bays. These areas provide optimal conditions for flounder, often characterized by soft, muddy, or sandy substrates where they can effectively conceal themselves from both predators and prey.
Many flounder species also extend their range to deeper ocean floors, including the continental shelf, at depths reaching up to 100 meters. These environments are defined by particular salinity levels, consistent currents, and suitable bottom compositions.
Estuaries, where freshwater mixes with saltwater, are particularly important habitats for many flounder species. These brackish areas are rich in nutrients and serve as significant feeding grounds and nursery habitats for young flounder. Juvenile flounder frequently prefer the shallow waters within these estuaries, utilizing locations like salt marsh creeks and seagrass beds for essential shelter and abundant food sources.
Seasonal migrations occur between inshore and offshore waters, reflecting their responses to changing environmental conditions, particularly water temperature. This movement ensures they remain in optimal conditions throughout the year for foraging and successful reproduction.
Unique Adaptations for Saltwater Life
Flounder possess biological adaptations that enable them to thrive in marine environments. Their distinctly flattened body shape allows them to lie almost completely flat on the ocean floor, a crucial feature for their bottom-dwelling existence. This morphology aids in their survival by making them difficult for both predators and prey to detect within their chosen habitats.
One of their most recognized adaptations is their camouflage ability. Flounder can rapidly change the color and pattern of their skin to match the surrounding seabed, a feat accomplished through specialized pigment cells called chromatophores. This dynamic color change allows them to blend seamlessly with various substrates like sand, gravel, or rocky bottoms, effectively vanishing from view.
A developmental adaptation is the migration of their eyes. Larval flounder are born with one eye on each side of their head, resembling typical fish. As they mature, one eye gradually moves over the top of the skull to the other side, resulting in both eyes being positioned on the upward-facing side of their flattened body. This allows them to maintain a wide field of vision while lying flat on the seabed, observing their surroundings for opportunities and threats.
Flounder also exhibit osmoregulation, maintaining their internal salt and water balance in a hypertonic (saltier) environment. As marine fish, they continuously lose water to their saltier surroundings through osmosis and gain excess salt from the water they drink. To counteract this, flounder drink large quantities of seawater and actively excrete excess salts, primarily through specialized cells in their gills, while producing minimal, concentrated urine. This mechanism is crucial for their survival in a high-salinity environment.
Varieties of Flounder
The term “flounder” encompasses a diverse group of flatfish within several families, primarily Pleuronectidae and Bothidae. These families are often distinguished by which side their eyes migrate to: Pleuronectidae are known as “righteye flounders,” while Bothidae are “lefteye flounders.”
Examples include:
- The Summer Flounder (also known as fluke) along the Atlantic coast of North America, from Nova Scotia to Florida.
- Winter Flounder in similar North Atlantic coastal waters.
- The European Flounder in European waters.
- The Gulf Flounder in the Gulf of Mexico.
- The Olive Flounder in the North Pacific.