This color adaptation allows halibut to avoid detection by both prey and predator. Spawning takes place during the winter months with the peak of activity occurring from December through February. Most spawning takes place off the edge of the continental shelf in deep waters of 200 to 300 fathoms. Male halibut become sexually mature at 7 or 8 years of age, and females attain sexual maturity at 8 to 12 years. Females lay two to three million eggs annually, depending on the size of the fish.
Fertilized eggs hatch after about fifteen days.
Free-floating eggs and larvae float for up to six months and are transported up to several hundred miles by currents of the North Pacific. During the free-floating stage, many changes take place in the young halibut, including migration of the left eye to the right side of the fish. During this time the young halibut rise to the surface and are carried to shallower waters by prevailing currents. In the shallower waters, young halibut then begin life as bottom dwellers. Most young halibut ultimately spend from five to seven years in rich, shallow nursery grounds as in the Bering Sea.