The Olfactory Organ of the Barramundi Lates calcarifer (Latidae)

Abstract The olfactory organ of the barramundi Lates calcarifer has an anterior nostril in the form of a short forward-facing tube, a posterior nostril without a valve, an olfactory rosette of a arrow-shaped type located on the medial side of the olfactory cavity, and two ventilation sacs. The nostrils are separated by a nasal bridge without a veliform ridge, the relative width of the bridge decreases with age of the fish. The olfactory lamellae fill the entire olfactory cavity, in juveniles with a body length of 4.9–6.8 cm there are 15–19 of them, in males at first maturity with a body length of 59.0 and 60.0 cm—55 and 53 of them. A large number of lamellae indicates high functional capabilities of the olfaction. New lamellae are formed in the rostral part of the rosette, as the fish grows, they become larger and thicker, their shape changes. Secondary folding is absent. With age, the relative width of the septum increases. The lacrimal ventilation sac is larger than the ethmoidal one, the sac openings are located near the central part of the rosette, ventral and dorsal to it, respectively. When the jaws are opened and the ventilation sacs are expanded, water enters to the olfactory organ (upon the septum) through the anterior nostril, is divided into microstreams, passes between the lamellae and goes into the ventilation sacs. When the jaws are closed and the sacs are compressed, water is ejected through the posterior nostril. The protrusion on the caudal side of the internal opening of the anterior nostril is a morphological adaptation that ensures the separation of incoming and outgoing water flows. The study confirms the assumption that sensory specialization in barramundi is not expressed and different systems make similarly significant contributions to obtaining biologically important information about the environment.