Sockeye salmon, Oncorhynchus nerka are anadromous fishes, which hatch in freshwater streams, migrate to sea, and later return to their natal stream to spawn. Correspondingly, they undergo vast changes in behavior, morphology, and environment throughout ontogeny. However, the sensory systems that mediate these migratory patterns are not yet fully understood, and no study to date has explored changes to the nervous system across their full ontogeny at these key life history stages, which may provide additional insights into shifts in sensory specialization. This study investigated the changes in brain size and brain organization of O. nerka, across 5 different life stages (fry, smolt, maturing adult, migrating adult, and spawning adult). The relative size of 6 major brain regions (olfactory bulbs, telencephalon, diencephalon, optic tectum, cerebellum, and medulla) was assessed using the ellipsoid method. As documented in other species with indeterminate growth, brain size increases significantly with body mass throughout ontogeny in O. nerka, with a steeper period of allometric growth during fry and smolt life stages, before tapering off at sexual maturity. Trends show allometric scaling of major brain regions varies throughout life, which may reflect the varying sensory requirements at key life history stages. These findings aid in better understanding of the development of the brain throughout life, highlighting that critical ontogenetic shifts in behavior and habitats may coincide with shifts in central development.