The terms “flounder” and “fluke” often cause confusion, though fluke is actually a specific type of flounder. While both are flatfish, they represent distinct species. This article clarifies their shared characteristics and unique features.
Shared Traits of Flatfish
Flounder and fluke belong to the biological order Pleuronectiformes, encompassing all flatfish. These fish share a unique flattened, oval body plan, adapted for their bottom-dwelling lifestyle. They lie on one side, camouflaging themselves against the ocean floor to ambush prey. As larvae, one eye migrates to the other side of their head, allowing both eyes to remain on the upward-facing side. This repositioning provides a wide field of vision while they rest on the seabed. Their ability to change coloration also enhances their predatory and defensive capabilities.
Distinguishing Features
The most definitive way to distinguish a fluke from other flounders is by eye placement. Fluke, scientifically known as Summer Flounder (Paralichthys dentatus), are “left-eyed” or sinistral. This means both eyes are on the left side when viewed with its dark side up and head pointing left. Conversely, many other flounder species, such as Winter Flounder, are “right-eyed” or dextral, with both eyes situated on the right side when oriented the same way.
Beyond eye placement, physical differences extend to their mouth structure and body shape. Fluke possess a larger mouth with sharp, noticeable teeth, indicating a more aggressive predatory nature. Other flounder species tend to have smaller mouths with less prominent teeth.
Fluke have a more elongated, oval body with a noticeable arch in their lateral line above the pectoral fin. Their coloration is often a lighter brown or gray, sometimes featuring distinct ringed, eye-like spots. In contrast, some flounders, like Winter Flounder, may have a more rounded body and a darker, uniform brown coloration. Fluke also grow larger than other flounders, often reaching 20-30 pounds.
Geographic Distribution and Naming
The term ‘flounder’ broadly refers to diverse flatfish species found worldwide. However, ‘fluke’ is the specific common name for the Summer Flounder (Paralichthys dentatus). This species is most abundant along the Atlantic coast of the United States, ranging from Nova Scotia to Florida, with significant concentrations from North Carolina to Massachusetts. Other flounder species, like Winter Flounder, inhabit colder waters further north, extending from Maryland into Canadian waters.
Regional naming conventions contribute to the confusion between these fish. In some areas, particularly the Northeast United States, ‘fluke’ became popular because the Summer Flounder’s left-eyed nature was considered an “anomaly” or a “fluke” compared to more common right-eyed flounders. Consequently, while all fluke are flounders, not all flounders are fluke, as the latter refers to one specific species within the larger flatfish family.
Preparing and Eating
Both fluke and various flounder species are highly regarded for their mild, delicate flavor and lean, white flesh. They are versatile fish, prepared using various cooking methods like grilling, baking, pan-frying, or steaming. Despite similarities, subtle differences in texture and taste can be noted.
Fluke is prized for its slightly sweeter taste and firmer, smoother texture. This firm texture makes it suitable for raw preparations like sushi or sashimi, where its delicate qualities are appreciated. Other flounder species, while equally delicious, may offer a different texture, sometimes described as slightly softer or having a unique flavor profile. Both fish provide a healthy source of protein and beneficial nutrients.