Halibut and flounder are both flatfish, belonging to the Pleuronectiformes order. While halibut are a specific type of flounder, not all flounder are halibut. They are distinct in several ways.
Key Physical Distinctions
A primary way to differentiate these flatfish is by their size. Halibut are notably larger, with Pacific halibut reaching over 400 pounds and Atlantic halibut capable of growing up to 710 pounds and 15 feet in length. In contrast, most flounder species are considerably smaller, typically weighing between 2 to 3 pounds, and seldom exceeding 20 to 30 pounds.
Their body shapes also offer clear distinctions. Halibut tend to have an elongated, diamond-like shape, characterized by pointed dorsal and anal fins and a concave tail. Conversely, flounder typically exhibit a rounder or more oval body with tails that are usually rounded or straight-edged.
Halibut are almost exclusively “right-eyed,” meaning both eyes are on the right side of their head, while flounder species can be either “right-eyed” or “left-eyed.” Halibut generally have smooth scales, whereas some flounder species possess scaly skin that can feel rough.
Habitat and Lifestyle
Halibut prefer the colder, deeper waters of the North Pacific and North Atlantic Oceans. They are typically found on sand, gravel, or clay bottoms at depths ranging from 50 to 2,000 meters, though they may move to shallower areas seasonally. Their geographic distribution spans from Alaska and California to Labrador, Greenland, and the Barents Sea.
Flounder, however, inhabit a broader range of environments, including coastal waters, estuaries, and even freshwater rivers. They generally prefer shallower depths, often less than 100 meters, though some species migrate to deeper offshore waters during colder months.
Halibut are predatory fish; their adult diet includes other fish like pollock, cod, and rockfish, as well as octopus, herring, crabs, and clams. Younger halibut feed on plankton and small crustaceans. Flounder are opportunistic bottom feeders, consuming zooplankton and small crustaceans as juveniles, and progressing to baitfish, shrimp, and other small invertebrates as adults.
Halibut have a longer lifespan, often living up to 50-55 years, with females growing larger and faster. Flounder typically have shorter lifespans, averaging 7 to 11 years.
Culinary and Nutritional Comparisons
Both halibut and flounder are prized in culinary applications, though they offer different experiences. Halibut is known for its mild, sweet flavor, often compared to cod or haddock. Its flesh is firm, thick, and meaty with large flakes, providing a steak-like texture that holds up well to various cooking methods. This firm texture makes halibut an excellent choice for grilling, baking, roasting, broiling, and pan-searing. However, its leanness means it can dry out if overcooked.
Flounder, in contrast, offers a mild, delicate flavor with a slightly sweet undertone, and is generally considered not “fishy.” Its texture is soft, delicate, and flaky, with thinner fillets. This delicate nature makes flounder well-suited for pan-frying, baking, or steaming, as it can be too fragile for grilling. It also requires careful cooking to prevent it from becoming dry.
In terms of availability and cost, flounder is typically more common and budget-friendly, while halibut usually commands a higher price. Nutritionally, both fish are good sources of protein and beneficial omega-3 fatty acids. Halibut is particularly lean, providing around 22.5 grams of protein per 100 grams, and is rich in B vitamins, potassium, selenium, and phosphorus. Flounder is also a lean protein source, containing vitamin B12, niacin, phosphorus, selenium, and vitamin D, with a lower fat content than halibut.