Ma. Salem et Y. Omura, LIGHT AND ELECTRON-MICROSCOPIC STUDIES ON THE DEVELOPMENT OF THE INNER-EAR AND OTOLITH OF THE AYU PLECOGLOSSUS-ALTIVELIS, Fisheries science, 64(2), 1998, pp. 259-264
The development of the inner ear, especially sensory maculae and otoli
ths, was studied in the ayu Plecoglossus altivelis, using light and el
ectron microscopy. Light microscopy indicated: 1) The auditory vesicle
first appears by 3 days after fertilization, The saccular macula over
lain by a round otolith appears and possesses apical hairs by 4 days,
while the utricular macula appears by 5 days after fertilization. 2) 9
days after fertilization (hatching day), both the saccular and utricu
lar maculae are well differentiated: composed of hair cells and suppor
ting cells, and overlain by saccular and utricular otoliths, respectiv
ely. Electron microscopy revealed: 1) By 5 days after fertilization, s
ensory hair bundles and bud-like microvilli protrude from the apical s
urface of the saccular and utricular maculae into the endolymphatic lu
men. 2) Secretory materials, such as electron dense cytoplasmic extrus
ions, vesicles containing spherules, and dense granules, seem to occur
from the apical surface of sensory epithelium, probably supporting ce
lls, and to contribute to the formation of the otolith and/or otolith
increments. 3) By 9 days after fertilization, the saccular otolith pos
sesses an inner incremental layer around the central nucleus and a thi
ck belt of peripheral incremental layer. Consequently, it was suggeste
d that the hearing mechanism in the ayu may be established earlier com
pared with other fishes.