鰻魚屬體表花紋與棲地利用之關係：以日本鰻及鱸鰻為例

Abstract

目前全世界共發現了十九種淡水鰻魚，依據其體色及花紋可分為兩類：體色斑斕且具花紋的花鰻與體色均勻而不具花紋的灰鰻，成長時期的花鰻與灰鰻在世界地理分布上會有許多重疊的區域，他們雖然共同存在許多河川中，但經常會有分棲於不同河段的現象發生，因此我們想探究淡水鰻魚對棲地的選擇與其體表花紋之間的關連，此外，鰻魚體內也許存在某些分子機制用以調控或是適應牠們對棲地的選擇。首先，我們以整合分析的方式彙整過去文獻中對於各種淡水鰻的體色及棲地選擇的描述，找出淡水鰻魚對棲地的選擇與其體表花紋之間的規則，並且嘗試以台灣的日本鰻(代表灰鰻)及鱸鰻(代表花鰻)為例來驗證上述的棲地利用模式。再者，我們於台灣鳳山溪流域以電氣採捕法進行環境調查並且利用環境DNA的分析法加以佐證。在環境調查研究結果中，我們發現日本鰻通常會選擇在河川下游及河口棲息，而鱸鰻主要棲息於河川上游區域，並且在環境DNA分析法的結果中，我們也發現中下游區域能夠測得日本鰻以及鱸鰻的DNA的存在，而上游區域則僅能測得鱸鰻的DNA的存在，能夠推斷出日本鰻傾向於棲息在河川中、下游及河口區域，而鱸鰻則傾向於在河川上游區域棲息。淡水鰻於台灣的棲地分布狀況與十九種淡水鰻的整合分析研究得出的結論相符合，花鰻的體表花紋對於他們棲息在礫石底質的河川上游區域佔有優勢，而灰鰻的體色則可能促使他們選擇棲息於砂泥底質的河川下游，透過與棲底環境相似的花紋來偽裝，作為黃鰻時期的躲藏及掠食優勢。此外，我們還研究了可能與其往上游遷徙能力及傾向有關的基因，利用RT-qPCR的分析法比較玻璃鰻時期日本鰻與鱸鰻的腦內及肌肉的基因表現量差異，結果顯示較高的認知能力以及快速泳動力的肌肉纖維組成，可能是促使鱸鰻能夠向上游遷徙的關鍵。

There are 16 species and 3 subspecies of Anguilla being reported worldwide. The eels could be divided into two categories, skin marbled (marbled eels) or skin uniformly colored (plain eels), by surface coloration. The world geographical distribution of the marbles eels and plain eels overlapped in their growth stage. They coexist in the same rivers but grow in the particular region of the river. Therefore, we would like to explore the possible relationship between Anguilla eels coloration and their habitat usage. Additionally, we also explore the molecular mechanisms might be existed to regulate or adapt their choice of habitat. First, we reviewed the previous studies for the eels coloration and habitat tendency to find the relationship between Anguilla eels coloration and their habitat usage, and tried to use A. japonica (as skin uniformly colored) and A. marmorata (as skin marbled) in Taiwan as an example to verify the habitat usage model. Eel distribution in Taiwan was detected by field investigation and environmental DNA (eDNA) analysis. The results of field investigation demonstrated that A. japonica is dominant in the lower reach of the river and estuary, while A. marmorata dominates in the middle to upper reaches of the river. We also found that eDNA derived from A. japonica and A. marmorata was detected at lower reach to middle reach of the Fengshan River, but there was only A. marmorata detected at the uppermost sites in the results of eDNA analysis. The distribution of eels in Taiwan coincides with the results of meta-analysis of eel coloration and habitat choice, the marbled eels may dominate in the middle to upper reaches of the river because of the gravelly environment. In contrast, the sandy and muddy substrates of downstream region may be attractive to the plain eels. The skin pattern of eels would allow a closer match to the visual characteristics of the background, serving as camouflage on yellow eel stage. Moreover, the potent genes in glass eels which may associate with the potential of their upstream migration was also investigated. We suggest that cognitive processes such as learning and memory acquisition and swimming-related muscle fibers composition are involved in upstream migration of A. marmorata.