Vol.2 No.3 -8 : Light and electron microscopic observations on the development and structure of the inner ear in the brown-spotted grouper Epinephelus chlorostigma (Serranidae, Teleostei).

By : Mostafa A. Salem

Abstract

The development and structure of the inner ear were studied in the brown-spotted grouper Epinephelus chlorostigma, using light and electron microscopy. Light microscopy indicated: 1) The auditory or otic placode first appeared at 18 hours after fertilization (hatching time). It excavates forming a small sac called otic vesicle at 20 hours after fertilization. 2) At 24 hours (one day) after fertilization, the vesicle enlarged in size having a wide cavity with thin walls. 3) At two days after fertilization, the anterior and posterior semicircular canals seemed to be the first formed , while, the horizontal canal, the utricular and saccular cavities are differentiated at four days after fertilization. 4) At six days after fertilization, the saccular macula covered by an elongated otolith and the neuromasts of the ampulla in the semicircular canals are well established. 5) The crista ampullaris in the semicircular canals and the sensory regions in the utricular and saccular maculae become well visible and differentiated at nine days after fertilization. It was suggested that the hearing mechanism in the E. chlorostigma may be established early compared with other fishes. Electron microscopy on the sensory areas of the inner ear revealed: 1) The saccular macula contained two types of hair ciliary bundles; type C1 bundles characterized by short graded stereovilli and kinocilium that was approximately three times longer than the largest stereovillus and type C2 bundles consisted of a series of long graded stereovilli and a kinocilium that was no more than two times longer than the longest stereovillus. 2) The utricular macula contained type C3 bundles and type C4 ones. The type C3 bundles had a limited number of graded stereovilli and a kinocilium that had the same length of the longest stereovilli or somewhat longer, while the type C4 hair bundles consisted of numerous stereovilli with the same length and without a kinocilium. Three types of connectors (links) between the stereovilli were observed. The different types of ciliary bundles and sites of connectors are possibly of functional importance.

8. Light and electron microscopic observations on the development and structure of the inner ear in the brown-spotted grouper Epinephelus chlorostigma (Serranidae, Teleostei).
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