兩棲洄游型蝦虎魚日本禿頭鯊的初期生活史及加入動態之研究

Abstract

日本禿頭鯊（Sicyopterus japonicus）是台灣東部溪流中常見的兩棲洄游型 ( amphidromy）蝦虎科（Gobiidae）魚類，洄游於海洋和淡水之間，而洄游的目的和生殖無關。本研究於1995年9月至1997年4月，於台灣東北部隆隆溪及其河口域採集日本禿頭鯊之標本。利用耳石的微細構造（日周輪、變態輪及鹽度輪等）及耳石微化學（鍶鈣比）所提供之訊息，配合環境因數，來研究日本禿頭鯊之初期生活史及加入動態。 由耳石鍶鈣比之變化以及耳石微細構造之特徵，發現稚魚進入淡水之後 2 星期左右形成變態輪，之後耳石的成長速率急速變快。上顎結構之改變可能是造成成長加速的原因。日本禿頭鯊稚魚到達河口時的平均體長為 33.95mm （範圍 30－38mm 、 n = 384 ) ，平均日齡為 163.72 天（範圍 125 －212 天， n = 277 ）。其加入期與回推之產卵期似乎和降雨量及水溫有關。經週期性迴歸分析（ periodic regression analysis ）結果顯示，日本禿頭鯊加入時的體長和日齡有一季節性之週期變化，兩者週期性之相位相反。加入期稚魚的體長和日齡之週期性變化可能與其後期仔魚階段的海洋浮游期的餌料生物量的季節性變化有關。

Sicyopterus japonicus, a common species of amphidromous Gobiidae fish, widespread in the stream of eastern Taiwan. In this study we used the information achieved from otolith microstructure and microchemistry (Sr: Ca) of the fish collected in the Long-Long brook and its estuary from September 1995 through April 1997 as well as environment factors to investigate the early life history and recruitment dynamics. Changes in otolith microchemistry and microstructure suggest that metamorphosis check is deposited at the time approximately two weeks after migration form sea water into freshwater. The growth of otolith dramatically increases after metamorphosis. The change of jaw structure of the fish may contribute to the dramatic growth. The total lengths of Sicyopterus japonicus juveniles at recruitment to the Shung-Chi River estuary were 33.95 mm in average (range 30-38 mm, n=384 ) and daily age were 163.72 days ( range 125-212 days, n=277 ). The timing of recruitment of the juvenile fish and their spawning season back-calculated from sampling date are correlated with precipitation and water temperature. Both length and age of the juvenile at recruitment to the estuary show a periodic change and the peak phase of change is reverse between length and age. The periodic change in both length and age depends on the seasonal change of productivity during their postlarval stage in the ocean.