||Growth of the Medaka (V) – Formation and Development of Otoliths in the Inner Ear During Metamorphosis
55 , 2017-03-01 , 愛知教育大学
The purpose of the present study is to provide information on formation and development of otoliths in the inner ear during the period of growth of the medaka from larva to juvenile. Before hatching, there are already two kinds of otoliths i.e. utricular and saccular otoliths in the optic capsules. After hatching, lagenar otoliths newly form in the most posterior region of the membranous labyrinth. Lagenar otoliths in one side of the lateral inner ear appear first in larvae about 6 mm total length (TL). The first otoliths form morphologically as a conglomerate of small granules or spherules. Frequency of individuals with lagenar otoliths increases linearly in proportion to the body size from about 6 mm to 9 mm TL. In larvae more than about 5 mm TL each otolith increases in diameter proportional to body growth, although large saccular otoliths exhibit a slightly steeper rise in diameter in comparison with other otoliths. As a whole, otoliths also exhibit a slow increase in thickness proportional to body growth during metamorphosis.