Abstract
The writer observed the growth increments in recent and fossil fish otoliths. For this purpose, the polarizing microscopy, microradiography and staining were used. The season of hatch, age and season of death of fossil fish were determined from the observation of incremental layers of fossil fish otoliths. The pattern of incremental layers of recent fish otoliths was related to the depth under sea level in which their fishes had lived. Most of Pliocene fossil fishes investigated in this study are considered from the pattern of incremental layers of their otoliths to have lived in the same depth under sea level as the recent fishes of the same genus do. But it is considered that some fishes, such as Diaphus, which live in the deep sea now lived in the somewhat shallower sea than recent during Pliocene. The change in width of a pair of thin growth bands, 1 to 4 μm wide, consisting of a thin light band and a thin dark band in ground sections of recent fish otoliths coincides almost with the periodic change in height of the tide. An obscure thin dark band exists within a thin light band. The facts above-mentioned support the theory that a pair of thin growth bands is not a daily increment but one with an average period of 24 hours and 50 minutes. The writer could observe their tidal growth increments in ground sections of Pliocene fossil fish otoliths.
