Inner Ear and Otolith Morphology of Climbing Perch Anabas testudineus (Anabantidae)

Abstract

The inner ear position and structure, related parts of the brain and neurocranium, as well as the morphology of the lapillus, sagitta, and asteriscus, are described in climbing perch, an obligate air-breathing fish capable of terrestrial movements. The olfactory bulbs and telencephalon are well developed. The dorsal protrusion with two symmetrical lobes is observed on the dorsal posterior surface of the telencephalon. The almost triangular rear part of the brain capsule and a narrow posterior region of the neurocranium represent the border of the suprabranchial chamber. The pars superior of the inner ear is located along the internal triangular part of the brain capsule, and both crus communis and ductus semicircularis posterior are located close to each other in the narrow extreme rear region of the brain capsule. The sacculus is enclosed in the large oval bony capsule (saccular swelling), and the sagitta is large with the average otolith length–total body length (TL) ratio equal to 0.06. Linear growth of the lapillus and sagitta is characterized by negative allometry in relation to body length. Despite the slow growth rate of the lapillus, its shape substantially changes during the growth of the fish 36–205 mm TL that, most likely, reflects increasing locomotion complexity. Possible adaptations of climbing perch inner ear to terrestrial movements are discussed.