Age and Birth Date of the Glass Eel, Anguilla japonica, collected in Taiwan

Abstract

Forty glass eels, Anguilla japonica, collected at the Giese shore and the Tanshui River mouth in Taiwan were aged with the otolith daily increments, and their birth dates were analyzed. The mean radius of sagitta was 153μm, and the mean width of increments was 1.3μm until about 50 days and 1.7μm during 50-90days. The mean age of the fish collected on January 3 was estimat-ed as 122d while that of March 9 sample was 120d. There were no significant differences in age and body length between the two samples The mean birth date of the January 3 samples was September 2, while that of the March 9 samples was November 9 of the previous year. They were significantly different, suggesting that fish born earlier in the spawning place migrated earlier to Taiwan with constant age and size. Spawning season of the Japanese eel might be summer-autumn contrary to the previous understanding (winter), and the time required for oceanic migra-tion would be only 4 months.