Early life history and recruitment dynamics of an amphidromous goby Sicyopterus lagocephalus as inferred from otolith microstructure and microchemistry

寬頰瓢鰭鰕虎(Sicyopterus lagocephalus)為兩棲洄游型(amphidromy)魚類，在淡水與海水之間洄游，其中，初期生活史的階段一直是個謎。本研究於2008年9月至2009年11月期間，每月於臺灣東部秀姑巒溪河口處(測站1)及河口往上兩公里處(測站2)採集樣本，同時於臺灣南澳及蘭嶼採集數量不等的標本。利用耳石微細結構(日週輪、變態輪、輪寬)及微化學(鍶鈣比)的分析，配合外部形態變化，以探討該種仔稚魚在溯河過程中的初期生活史特徵，和回推其產卵期，並探討海洋浮游期(pelagic larval duration)的地理差異及其可能的擴散路徑。 結果顯示，秀姑巒溪的寬頰瓢鰭鰕虎為全年產卵型，且每個月皆有個體加入。其上溯行為俱日行性，主要集中於白天的12:00 – 15:00時段。依照外部型態，捕捉的樣本個體可分為五個發育階段：分別為後期仔魚的第一期(PL1)和第二期(PL2)、以及稚魚的第一期(J1)和第二期(J2)以及成魚(A)，上溯中的個體其最明顯的外形變化包括口部位置由前端位(terminal)轉變成次端位(inferior)；尾部形狀由叉型尾(fork-shape)改變為圓型尾(round-shape)。測站1以PL1期為主(93%)；測站2則以J1期為主(78%)。仔稚魚加入河口的平均體長為27.7 mm (範圍25.6-29.8 mm, n = 99)，平均日齡為115天(範圍84 – 162天, n = 49)，平均體成長率為0.23 mm/天 (範圍0.20-0.27 mm/天, n = 49)，兩測站間的個體長有顯著性差異(p0.05)。初期階段的耳石日成長率呈現先升後降的趨勢並持續到變態輪，輪後的成長率才再度回升，且最大成長軸由耳石後端轉換至其他軸。而耳石鍶鈣比在核心部分與變態輪後有顯著較低的現象，其PLD與加入體長在臺灣東部有南低北高的地理傾斜現象存在。本研究對於臺灣寬頰瓢鰭鰕虎建立基礎的生態資料，有助其物種與棲地保育的政策制定提供參考。Sicyopterus lagocephalus (Gobiidae: Sicydiinae) is an amphidromous goby and the basic details about its early life history like the duration of pelagic larval stage is still a mystery. In this study, we have used of the otolith microstructure (daily growth increments, metamorphosis check, and increment width) and microchemistry (Sr/Ca ratio) of S. lagocephalus collected from 2 stations in the lower reaches of Hsiukuluan River and from Nanao and Lanyu in eastern Taiwan to understand its early life history, dispersal ,and recruitment dynamics. The results showed that S. lagocephalus has a whole-year spawning and recruitment period. Recruitment time occurs mostly during the day with the peak at around 15:40. Based on external morphology, the specimens were characterized into five stages: post-larval stages PL1, PL2; juvenile stages J1, J2 and adult stage (A). PL1 stage individuals were mostly found in station 1 (93%) while J1 stage individuals in station 2 (78%). The total length of S. lagocephalus at recruitment to the estuary of Hsiukuluan River were 27.7 mm (range 25.6-29.8 mm, n = 95) with daily age at about 115 days (range 84-162 days, n = 49), and somatic growth rate at about 0.23 mm/d (range 0.2-0.27 mm/d, n = 49). No significant differentiation among seasons were observed (p>0.05). The growth rate was slow at the beginning of larval life; it increased first and then decrease until recruitment to the freshwater. It increased again after the deposition of the metamorphosis check but exhibited asymmetrical growth afterwards. The otolith Sr/Ca ratio in the core was low at the beginning of larval life and it then drastically increase as the fish migrates toward the sea. It will start to decrease as soon as the fish migrates back to the freshwater. Also, there was a geographic decline in the length at recruitment and PLD of S. lagocephalus larvae from south to north in eastern Taiwan. This study has allowed us to improve our knowledge on the early life history and recruitment dynamics of this species, and help managers to implement conservation methods