Abstract
Early formation of otolith was studied on artificially hatched larvae of the Japanese eel, Anguilla japonica. Newly hatched larvae had a pair of sagittae which were flat and subelliptical with 8.3μm in mean diameter. The diameter of the sagitta increased linearly with age. No growth increments were observed in the sagitta at hatching, while larvae which were 2, 4 and 6 days old had on average 2.1, 3.6 and 6.0 increments, respectively. The number of the increments (Y) and the age in days after hatching (X) showed a close linear relationship (Y=0.96X+0.06, r=0.913, n=40), suggesting daily deposition of sagittal increments. In 95% of the field-caught elvers of this species, a distinct dark ring (check) with the diameter of 6-12μm was found around the nucleus of the sagitta. This seems to be a “hatch check” deposited at hatching, since its diameter roughly agreed with that of the sagitta in the newly-hatched larvae. Possibly, the number of the increments outside the hatch check represents the age of the fish in days.
