Morphology of the Olfactory Organ in the Climbing Perch (Anabas testudineus, Anabantidae, Perciformes)

The structure of the olfactory organ in the climbing perch (Anabas testudineus) has been studied by light microscopy. The anterior nostril is a short and narrow tube directed forward. The posterior nostril in large individuals (TL > 8-10 cm) is almost completely overlapped by the skin valve fold originating at a fish body length of TL 6.0 cm and gradually increasing in size. The rostral part of the olfactory cavity is occupied by a parallel-type olfactory rosette. The number of lamellae in the rosette increases as the fish grow, but does not exceed 11 cm (TL 22 cm). The olfactory lamellae in the center of the rosette are the largest in size, these being reduced toward the medial and lateral edges of the rosette. Secondary folds on the lateral sides of the lamellae appear in fish that reach a TL length of 6.5 cm. The openings of two ventilation (accessory) sacs, i.e., a large lacrimal and a less voluminous ethmoidal, are located in the caudal part of the olfactory cavity. A diagram of olfactory cavity ventilation is proposed. The possible use of olfaction by the climbing perch for terrestrial orientation and navigation is discussed.