Aspects of the early life history of the Japanese eel Anguilla japonica determined from otolith microstructure.

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Otoliths (sagittae) of 22 elvers of Anguilla japonica which were collected in southern Kyushu, Japan, in December 1981 and January and March 1982, and in northern Taiwan in November 1981, and of two artificially hatched larvae were examined using scanning electron microscopy. Otoliths of five elvers of A. marmorata from the same places were also observed. The arrangement and other characteristics of otolith rings in both species were similar to those of the daily rings known for other species. The total number of rings in A. japonica for the November, December, January and March samples averaged 130.8, 155.2, 163.7 and 169.8, and that in A. marmorata for the November and January samples was 146.3 (mean) and 133, respectively. The otolith of 6 day old larvae indicated that the first ring in the elvers was not formed at hatching. The spawning time was estimated to be June-October 1981 for A. japonica, and May-August 1981 for A.marmorata, respectively. The three samples from southern Kyushu differed with each other in the time of spawning, the location of and/or the route from the waters they were spawned. The December elvers may have grown faster than the March elvers.