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Halibut spawn between November and March. Though it is believed they spawn annually, there is evidence to suggest they may "skip spawn", or reproduce every other year. During the winter months, halibut will migrate from their relatively shallow feeding grounds to deeper waters along the edge of the continental shelf (180-450 meters).

Pop-up Archival Transmitting tag data have recorded periods where halibut swim up off the bottom and drift back down to the sea floor. They'll repeat this several times. While we're not certain what this behaviour is, it seems to conform with "spawning rises" witnessed in other flatfish, where females move up into the water column to release eggs while accompanying males fertilize them. This mechanism would allow for better egg dispersal. Numbers of eggs vary with the size of the female: a 50-pound (23 kg) fish will produce around 500,000 eggs while a 250 lb (113 kg) female may produce over 4 million.

Larva (Stage 1)


Approx. 9 mm in length
After about 15 days, the drifting eggs hatch. Halibut start off in an upright position, with eyes on either side of its head. The larva are neutrally buoyant and are transported by the ocean currents. Note the large yolk sac which will sustain the fish till the early post-larva stage.

Post-larva (Stage 3)


Approx. 16 mm in length
At this point, the yolk sac has been fully absorbed and the fish will begin feeding on planktonic organisms.

Post-larva (Stage 7)

mid post-larva

Approx. 21 mm in length
The young fish is still riding the currents. During its development, a post-larva can travel hundreds of miles in the Alaska Stream, which runs counter-clockwise in the Gulf of Alaska. Currents can run in excess of a mile (1.6 km) per hour in some coastal regions, but, typically, speeds are 3-5 miles (5-8 km) per day.

Post-larva (Stage 9)

late post-larva

Approx. 25 mm in length
The metamorphosis begins: the left eye moves over the snout to the right side of the head and pigmentation on the left side fades.

Young halibut

young halibut

Approx. 35 mm in length
Six months after hatching, the young halibut has developed the characteristics of the adult form and is ready to settle in the shallows of inshore areas.

Photo by Brooks

The Pacific halibut, or Hippoglossus stenolepis [from the Greek hippos (horse), glossa (tongue), steno (narrow), lepis (scale)], is one of the largest species of teleosts. Its scientific name was first proposed in 1904 by P.J. Schmidt, a Russian scientist who noted anatomical differences such as scale shape, pectoral fin length, and body shape which Schmidt thought distinguished it from the Atlantic halibut (Hippoglossus hippoglossus).


Max. length
8+ feet (2.5 meters)

Max. weight
approx. 500 pounds (230 kg)

Max. recorded age:
Female - 55 years
Male - 55 years

Santa Barbara, CA to Nome, AK
(N. American coast);
Gulf of Anadyr, Russia to Hokkaido, Japan (Asiatic coast)

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Advisory Bodies

Advisory Bodies Feature

The IPHC maintains an auxilary website for its Advisory Bodies at iphc.info.