Age,Growth and Reproduction of the Tile Fish Branchiostegus Japonicus in the Waters Around Guei-Shan Island,Northeastern Taiwan

Abstract

為瞭解日本鰻之降河洄游行動，1994年1月26日～29日將超音波發射器裝在5尾經人工催熟之種鰻（平均體重1，044 g，全長83.3 cm）體上，於台灣西南部之小琉球海域放流後追蹤其洄游行動。其中2尾游向東南方，另2尾則游向西北方，洄游之方向與放流點當時之海流流向幾乎一致。剩餘1尾在放流後的5分鐘內即失去信號。追蹤結果，發現其游動距離為490 m～750 m，平均為658 m。平均游泳速度為0.48～40.1 m/sec，但個體間之差異不大。由上述之結果推測種鰻在放流後可能立即潛入海底之洞穴中藏匿，然後再慢慢進出洞穴活動。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.