|Abstract: ||四絲馬鮁(俗名午仔魚)為台灣西部沿岸重要經濟性魚種，包含多鱗四絲 馬鮁(Eleutheronema rhadinum)及四絲馬鮁 ，為 了解四絲馬鮁漁業資源結構並嘗試分辨養殖放流個體，本研究利用外部形態(側線有孔鱗、側線上方鱗列數、側線下方鱗列數、鰓耙數、胸鰭膜顏色及側線末端分岔情形)，以及應用耳石核心微化學分析(鍶/鈣、鋇/鈣、鎂/鈣、鐵/鈣及鉛/鈣比)，探討台灣西部海域四指馬鮁漁業結構組成。本研究自 2015年至 2018 年於淡水、苗栗、雲林港口共計蒐集 1316 尾四絲馬鮁生物樣本，每尾樣本皆測量體長、體重、外部形質以及耳石半徑及耳石重量;另為鑑別 MicroMill○R 高精確感應耦合電漿質譜儀測定耳石元素，以瞭解初期生活史環境特徵 與野生及放流個體間的差異。 研究結果顯示四指馬鮁外部形質特徵為胸鰭膜黃色，側線末端為分岔， 側線有孔鱗為 65-79，側線上方鱗列數為 8-12，側線下方鱗列數為 11-16， 鰓耙數為 9-12;測得多鱗四指馬鮁之外部形質結果為胸鰭膜黑色，側線末端 無分岔，側線有孔鱗為 80-98，側線上方鱗列數為 9-14，側線下方鱗列數為 10-18，鰓耙數為 8-12。本研究發現多鱗四指馬鮁之體長體重關係式、耳石 半徑與尾叉長關係式、耳石重與魚全重關係式經由最大概似法(likelihood ratio test)檢驗結果顯示，上述三者關係於地區間均無顯著差異，養殖與野生 個體之肥滿度比較結果顯示養殖個體肥滿度較高，多鱗四指馬鮁之耳石半徑 比例在各地區間無顯著差異，然而多鱗四指馬鮁耳石重量比例在不同地區間 則有顯著差異。 以高精確感應耦合電漿質譜儀分析耳石核心元素濃度比結果顯示，多鱗 四指馬鮁於地區間均無顯著差異，元素比例結果如下:Sr/Ca (1.72-2.71 mmol/mol)、Ba/Ca (10.52-21.25 mmol/mol)、Mg/Ca (0.17-0.50 mmol/mol)， 可作為往後判斷四指馬鮁地區耳石元素差異指標;本研究進一步使用此三種 元素濃度比及肥滿度、耳石半徑比例與耳石重比例，利用判別函數分析辨別 野生或養殖放流個體，結果顯示判別成功率為 90%，可作為往後區分之有效 工具。|
Both two species of fourfinger threadfin (Eleutheronema tetradactylum and E. rhadinum) are commercially important fishery resources in coastal waters off western Taiwan. However, they are rarely separated in the catches of coastal gillnet and set-net fisheries, preventing the understanding of their population dynamics. Fish samples of the two species were collected from the Tamsui, Miaoli, Yunlin, and Kaohsiung fishing ports in this study. External morphometric characteristics (the color of pectoral fins, lateral line squamation on the caudal-fin membrane and different scale counts of pored lateral line and those above and below the lateral line) and microchemistry of otolith core (trace elements including Sr/Ca, Ba/Ca, Mg/Ca, Fe/Ca and Pb/Ca ratios) were used to identify the two species of E. tetradactylum and E. rhadinum. Yellow pectoral membranes were found for E. tetradactylum, with branch lateral line on caudal fin base, scale counts of pored lateral line from 65 to 79, and scale rows above and below lateral line ranging between 8-12 and 11-16, respectively, while black pectoral membranes and un-branch lateral line on caudal fin base were identified for E. rhadinum, with scale counts of pored lateral line from 80 to 98 and scale rows above and below lateral line ranging between 9-14 and 10-18, respectively. The relationships between fork length and body weight, fork length and otolith radius, and body weight and otolith weigh were insignificant among sampling locations for E. rhadinum based on likelihood ratio tests. All the trace element ratios of otolith core were statistically insignificant among sampling sites, but otolith weight to body weight and the condition factor of reared E. tetradactylum were statistically higher than those for wild individuals. The trace element ratios of otolith core were found insignificant among sampling sites, but statistically differed between the released reared samples (Ba/Ca: 18.83±1.66 mmol/mol) and wild individuals (4.78±1.04 mmol/mol). In addition of trace element ratios, condition factors, otolith radius ratios and otolith weight to body weight were demonstrated to separate wild and released reared fish successfully. Results derived from this study suggest that external morphometric characteristics and trace element ratios of otolith core were considered useful tools to identify the two species of fourfinger threadfins.