Atlantic Halibut

The Atlantic halibut (Hippoglossus hippoglossus) is the largest of all flatfish species, a member of the family Pleuronectidae found in the cold waters of the North Atlantic. Like other flounders, it begins life symmetrical but undergoes metamorphosis so that one eye migrates, leaving both eyes on the right side of the body as an adult right-eyed flatfish. Atlantic halibut inhabit sandy, gravel, or muddy bottoms of the continental shelf and upper slope, ranging from the Barents Sea and Iceland to the eastern coast of North America. Historically heavily fished and slow to mature, the species is now considered depleted in parts of its range and is subject to conservation attention and stock management.

Atlantic halibut are identified by their large size and classic diamond-shaped flatfish outline.

• Body: broad, elongated diamond shape, thick and muscular compared to other flatfish
• Eyes: both on the right side (right-eyed flounder)
• Coloration: dark olive-brown, greenish, or blackish upper side, sometimes mottled; pure white underside
• Tail: slightly concave (lunate) rear edge, a trait distinguishing it from many other flatfish with rounded tails
• Size: among the largest bony fish, reaching well over 2 m Its combination of great size, concave tail, and dark uniform upper coloration separates it from smaller flounders like plaice or dab.

Atlantic halibut live on the continental shelf and upper slope of the North Atlantic, typically at depths from about 50 to 2,000 m, though most individuals are found between 100 and 700 m over sand, gravel, or clay bottoms. Water temperatures in their preferred range are cold, generally between 3 and 9°C. Their range spans from the eastern seaboard of North America, including the Gulf of Maine and Canadian waters, across to Greenland, Iceland, the Barents Sea, and the coasts of Norway and the British Isles. Juveniles tend to use shallower coastal nursery grounds before moving to deeper offshore waters as they mature.

Atlantic halibut are solitary, bottom-dwelling ambush predators that lie partially buried in sediment, using camouflage to surprise prey such as smaller fish, squid, and crustaceans, which they capture with a swift lunge. Unlike most flatfish, they are also capable of active mid-water swimming and can pursue prey more aggressively. They are slow-growing and long-lived, reaching sexual maturity only after several years, which makes populations vulnerable to overexploitation. Spawning occurs in deep offshore waters during colder months, with females releasing large numbers of buoyant eggs that drift and develop in the water column before larvae settle and metamorphose into bottom-dwelling juveniles.