Flounder is a common name applied to a diverse group of marine fish known for their remarkably flattened bodies and unique appearance. The fish are recognizable by their distinct asymmetry, which develops early in their life cycle. This specialized body structure allows them to live a life primarily on the ocean floor, blending seamlessly with the seabed. As a highly valued seafood, flounder is globally distributed across various marine and estuarine environments.
Defining Characteristics of Flounder
The most striking feature of the flounder is its compressed, disc-like body shape, which is an adaptation for its bottom-dwelling, or benthic, lifestyle. When a flounder first hatches, it looks like a typical fish, swimming upright with an eye on each side of its head. Within a few weeks, a process called metamorphosis begins. One eye migrates over the top of the head to join the other on the opposite side, resulting in an adult fish that lies on its side, with both eyes facing upward.
The side facing the seabed, known as the blind side, is typically pale white. The eyed side is pigmented and capable of remarkable color changes. This ability to instantly alter its coloration and patterning, known as camouflage, allows the flounder to perfectly mimic the substrate, whether sand, mud, or gravel. Flounder often burrow slightly into the sediment, leaving only their two independently moving eyes exposed to ambush prey and hide from predators.
Biological Classification and the Flatfish Order
Flounder belongs to the order Pleuronectiformes, the group of ray-finned fish commonly known as flatfish. This order is unique among vertebrates because its adult members lack bilateral symmetry, a direct result of the eye migration that occurs during development. The term “flounder” is not a formal scientific classification but a general common name used for several families within this order.
Within Pleuronectiformes, flounder are divided into two main groups based on which side their eyes migrate to. The family Pleuronectidae is often called “righteye flounders” because the eyes are typically on the right side of the body. Conversely, the families Bothidae and Paralichthyidae are known as “lefteye flounders” because their eyes are positioned on the left side of their head.
Common Species and Geographic Distribution
Flounder species are distributed across temperate and tropical marine waters worldwide, inhabiting the continental shelf in depths mostly under 200 meters. The Summer Flounder, also known as Fluke (Paralichthys dentatus), is found along the Atlantic coast of North America, ranging from Nova Scotia to Florida. This lefteye flounder often migrates seasonally, moving to shallow coastal waters and estuaries in warmer months and offshore to deeper water during winter.
Another well-known species in the North Atlantic is the Winter Flounder (Pseudopleuronectes americanus), a righteye flounder also known as blackback flounder. The European Flounder (Platichthys flesus) is widely distributed along the coasts of Europe, from Norway down to the Mediterranean. This species is notable for being one of the few flatfish that can tolerate and inhabit freshwater, often traveling significant distances up rivers from the sea.
Flounder in the Seafood Market
Flounder is a popular fish in the global seafood market, prized for its delicate, white, flaky meat and mild flavor. The fish is sold whole or in fillets and is suitable for various culinary preparations, including broiling, steaming, and sautéing. In the marketplace, the common name “flounder” is often used interchangeably with other flatfish names like “sole” and “plaice,” which can create confusion for consumers, although these names refer to distinct species.
Sustainability is a growing concern, prompting an increased focus on responsible sourcing and fishing methods. Some flounder stocks, such as those in the U.S. Atlantic, are rated as having moderate or serious environmental concerns depending on the location and gear used. Conversely, flounder and sole species from Alaska, often certified by the Marine Stewardship Council (MSC), are considered highly sustainable choices due to healthy populations and effective management.