Abstract
Upper jaw teeth of Sicyopterus japonicus are examined regarding their shape, development and replacement.The fish has a row of functional teeth and ca. 23 rows (31 mm SL) to ca. 40 rows (85 mm SL) of replacement teeth on their upper jaw. Replacement teeth shift their position in the gum with development, and at the last stage of their development a small bone is formed at the base of each tooth. Replacement teeth with the small basal bones completed move downward in the gum and set firmly on the premaxillary to become functional teeth. Old functional teeth replaced by new ones are gradually resorbed in the tissue of the upper jaw in the process of entering into a crevice of the premaxillary, and finally completely disappear. This resorption suggests that there is a possibility of the reuse of their components to produce new teeth. This replacement occurs every 9.2 days when the fish size (SL) increases 0.12 mm per one day (1.1 mm per 9.2 days). The fish probably needs tooth replacement frequently and resorption of the teeth because the upper jaw teeth wear out rapidly when feeding by scraping algae from the surface of stones with its teeth.
