Timing of metamorphosis and estuarine arrival across the dispersal range of the Japanese eel Anguilla japonica

Elvers of the Japanese eel Anguilla japonica Temminck & Schlegel were collected from 6 estuaries in Taiwan, China and Japan. The fish were aged by counting otolith daily growth increments. The time of metamorphosis from leptocephali to glass eels was determined from the otolith increments where the width and strontium:calcium ratios changed drastically. Age upon arrival at the estuaries (mean +/- SD) was 154.71 +/- 10.69 to 182.06 +/- 12.43 d, while age at metamorphosis was 115.8 +/- 8.13 to 137.85 +/- 11.28 d. Both ages showed a geographic dine that increased from south to north. The time from metamorphosis to arrival at the estuaries averaged 31.73 +/- 7.58 to 45.02 +/- 9.21 d. The lengthy duration of the leptocephalus stage and differences in the timing of metamorphosis are the principal factors in the long-distance dispersal of the eel.