However, when the larvae are approximately one inch long, they undergo an amazing transformation in which the left eye moves over the snout to the right side of the head and the pigmentation on the left side of the fish fades. The young halibut take on the features of adult fish approximately six months after hatching and settle to the bottom in shallow, nearshore areas. As halibut increase in size, fish make up a larger part of the diet. Besides pollock, sablefish, cod, and rockfish, large halibut also eat octopus, herring, crabs, clams, and smaller halibut. While halibut can live to be up to 40 years old, grow to over eight feet long, and weigh over 500 pounds, most halibut caught in the sport fishery will be 8-15 years old and weigh between 10 and 100 pounds.
Female halibut live longer and grow faster and larger than do males.
Few males exceed 80 pounds and generally all halibut over 100 pounds are females. The oldest halibut on record was a 42 year old female while the oldest male observed was 27 years old. The age of halibut is determined by a bony structure in the inner ear called an otolith. As the fish grows, annual growth rings are formed on the otolith, similar to rings on a tree. Halibut typically move to deeper waters as they grow older.