The word "halibut" comes from the Middle English "haly-butte," meaning "fat fish to be eaten on holy days." Today, one of the most researched and fished species of flatfish is the Pacific Halibut (Hippoglossus stenolepis). The Pacific Halibut is a large predatory member of the flatfish family, sometimes reaching three meters in length. The largest of all flatfish, halibut have extensive life spans. The oldest recorded female was 42 years old; the oldest recorded male 27 years. The largest Pacific Halibut ever caught by a sport fisherman weighed 495 pounds.
Physically, the Pacific halibut can weigh up to 800 pounds. It has an elongate, highly compressed, diamond shape, with both eyes on the right side. The eye side is dark brown and covered with fine mottling, with the color blending into the sea bottom. The opposite side (kept against the sea bottom) is lighter in color. It has a moderately sharp snout that contains a medium sized mouth. In the upper jaw there is a double row of sharp teeth. The fish's pelvic fins are symmetrically placed; the dorsal fin starts over the middle of the eye, with softer dorsal and anal fins at the middle.
Pacific Halibut spawning takes place in the winter, with peak activity occurring between December and February. Most spawning takes place off the edge of the continental shelf in deep waters between 200 and 300 fathoms. A male halibut become sexually mature in 7 or 8 years, with the females maturing between 8 and 12 years. A female halibut, depending on its size, can lay between two and three million eggs annually. The fertilized eggs hatch after about 15 days. The eggs and larvae fish free-float for up to six months, being transported several hundred miles across the North Pacific. When halibut are born, their bodies are "normal." They soon roll over onto their side, and the eye on the down turned side soon migrates to the top of the head, twisting the entire cranium. Young halibut soon rise to the surface currents, where they migrate into shallow waters, taking up life as bottom dwellers. They will then spend the next five to seven years in these nursing grounds, such as the Bering Sea.