利用生命條碼進行台灣周邊海域柳葉鰻之分類研究

Abstract

柳葉鰻(leptocephalus)為海鰱總目(Elopomorpha)的幼生，分類位階為條鰭魚綱、新鰭亞綱，海鰱總目包含鰻形目(Anguilliformes)、囊咽目(Saccopharyngiformes)、海鰱目(Elopiformes)、狐鰛目(Albuliformes)，其中台灣產鰻形目共有62屬157種，囊咽目有1屬1種、海鰱目有2屬2種、狐鰛目有5屬5種。柳葉鰻頭型狹長，且有著幾近透明、極側扁的身體，外覆一層薄薄的肌肉組織，身體肌節明顯，許多種類有色素斑分佈，與其成魚形態相差甚多。目前台灣附近海域柳葉鰻的描述尚未健全，因此本研究希望能藉由DNA生命條碼(barcode)輔助形態鑑定，將台灣附近海域柳葉鰻建立一個較為正確的檢索表。本研究之鰻形目仔稚魚樣本，分別在2007年7月到2009年11月間利用中層拖網(Isaacs-Kidd Midwater Trawl)，櫻花蝦中層拖網及浮游動物網於東北、西南及東海海域採集；2009年11月於東港下雜魚堆採集。共採集到528尾樣本，有效樣本為142尾，利用形態分出32個類型，鑑定出22個分類單元，共有6個科，3個亞科，10個屬，3個種；從142尾樣本中成功取得86條COI序列，將COI序列利用BOLD資料庫及冷凍遺傳資料庫進行比對，可將分類單元數目提升至24，包含5個到科，3個到亞科，7個到屬，9個到種及2個未知形態，其中1科2屬4種為台灣海域首次描述。由於柳葉鰻形態特徵較少，利用形態鑑定時大多僅能鑑定到科或屬的分類階層，故利用生命條碼比對則可將原本僅能鑑定到科或屬的物種鑑定至較低的分類階層；且原本以形態鑑定為線鰻科的柳葉鰻經由生命條碼比對後，修正為海鰻科的台灣絲尾海鰻。因此利用生命條碼進行仔稚魚鑑種不僅能補足形態特徵上的不足，亦能檢驗其形態特徵的有效性，與形態鑑定結果之正確性，有助於柳葉鰻的分類研究。然而由於生命條碼資料庫尚未健全，鰻形目成魚物種之生命條碼數目相對較少，涵蓋的比例較低，導致比對到的最相近的物種，與樣本的序列相似度皆不高。未來若能將成鰻生命條碼資料庫及柳葉鰻形態資料收集並建立完整，則可提供柳葉鰻鑑種的良好依據。

Leptocephalus is the larvae of the Superorder Elopomorpha which consist of four orders: Anguilliformes, Saccopharyngiformes, Elopiformes, and Albuliformes. Leptocephali are distinguished from other fish larvae by their extremely compressed and transparent body; they are also very different from their adult fish. Since leptocephali are not well described in the Taiwan area, this study aim to use barcoding to identify them in order to give better descriptions. For the morphological and COI identifications, a total of 528 leptocephali were collected by IKMT, shrimp trawl, and ring net in July 2007, June 2008, May-July 2009, and July 2009. Based on the morphological characters, 142 specimens could be classified into 32 types, and further identified to 22 taxa, including 6 families, 3 subfamilies, 10 genera, and 3 species, whereas, barcoding identified the specimens to 24 taxa, including 5 families, 3 subfamilies, 7 genera, and 9 species. Because leptocephali lack significant morphological characters, most of the specimens could only be identified to the family or genus level by morphology. DNA barcoding provides an efficient way to identify fish species: the number of species identified by the barcoding approach is more than that by morphology. It can also evaluate the morphological identification of fish larvae and improve the accuracy of identification. However, the BOLD database is not perfect as it still hasn’t included all the eel species. Therefore, it is necessary to make the COI database more complete for adult eels so that the barcoding identification of leptocephali can be carried out more thoroughly.