Abstract
Background:
Olfaction regulates animal behavior; hence its organs are seen early in fish development. Due to their aquatic lifestyle, fish employ olfaction to communicate chemical signals during gustation.

Aim:
In this study, we investigated the morphogenesis and ontogeny of the seabass's (Dicentrarchus labrax, Linnaeus, 1758) olfactory organ.

Methods:
SEM is used to study these organs' development in fries, fingerlings, juveniles, and adults.

Results:
Both placodes thickened and invaginated, generating simple olfactory pits with undifferentiated cells. Nonsensory and sensory olfactory cells emerged after the first day of hatching. Apart from occasional mucous goblet cells, ciliated receptor cells (CRCs) are more common than microvillous receptor cells. Long, thin, disordered kinocilia (KC) and small microvilli of ciliated and microvillous supporting cells cover some of the pit floor. The SEC-lined pit bottom deepens at 45 days from hatching. Fries develop tube-shaped anterior incurrent and broader posterior excurrent nostrils by the 75th day post-h, along with a broad epidermal nasal bridge. In this stage and after fingerling formation 90 days post-hatching, the bottom olfactory epithelium lining each chamber forms a multilamellar rosette of lamellae (OL) that radiate equally from a median raphe (MR). Fully mature seabass have 38–40 lamellae. The pseudostratified epithelia surrounding each lamella are sensory and nonsensory. The first one, scattered in islets between the second, has receptor (ciliated, microvillous, and rod-tipped) and supporting (ciliated and microvillar) cells, while the nonsensory epithelium has ciliated and microvillar supporting cells and masses of superficial epidermal cells. Goblet mucous cells and basal stem cells on the epithelium's basal lamina are abundant in nonsensory areas but rare in sensory parts.

Conclusion:
These findings underscore the functional specialization of olfactory cells, reflecting the organ's pivotal role in chemical communication and environmental adaptation throughout the European seabass's development.

Key words: Olfactory ontogeny, Olfactory placode, Olfactory receptor cells, Olfactory supporting cells