Artificially induced maturing Japanese eels,Anguilla japonica,were releasedin southwestern waters of Taiwan on 26-28 January 1994,and tracked with ultrasonic transmitter to collect informations on the spawning migration of this species.Among five eels tagged with identical transmitters,different type of signals,pulselength and frequency,two specimens moved southeastward(137.2 °),while theother two swam northwestward(328.4 °and 347.0 °).The direction of movement, except No.5 specimen,coincided with the tidal currents of release time andlocation.The last eel(No.5)was lost 5 minutes after release because of a rapidmovement.Northwestward movement of the eel might be explained as a preferencefor deeper waters,just as observed in European eel.The distance between therelease point and the end of tracking ranged from 490 m to 750 m.Mean swimmingspeed during tracking ranged from 0.5 to 40.1 cm/sec.The changes in strengthand direction of the signals indicated that the eels seemed to swim downward tothe sea bottom just after the release and might be moving in and out of a”shelter”or”hole”at the bottom.Once the eel dived and reached the bottom,theymight move little either horizontally or vertically.