日本一個研究小組在新一期英國《生物學(xué)通訊》雜志網(wǎng)絡(luò)版上發(fā)表文章說,，他們通過基因分析發(fā)現(xiàn)，鰻魚的祖先很可能是深海魚,。
鰻魚生活在河川,、湖泊等淡水中，但成年鰻魚會不遠(yuǎn)千里到深海產(chǎn)卵,。鰻魚這種獨(dú)特的洄游行為一直未得到很好的解釋,。
東京大學(xué)海洋研究所等機(jī)構(gòu)的研究人員以包括鰻魚科在內(nèi)、親緣關(guān)系較近的19科56種魚類為對象進(jìn)行了研究,。通過比較它們的全基因序列,，研究人員繪制出表示它們進(jìn)化軌跡的系統(tǒng)樹。結(jié)果顯示,，鰻魚科魚類與生活在熱帶海洋深處的線鰻科和鋸犁鰻科魚類的親緣關(guān)系非常近,。屬于線鰻科和鋸犁鰻科的一些魚類擁有巨大的嘴或者像喙一樣的顎，之前人們認(rèn)為它們與鰻魚的親緣關(guān)系較遠(yuǎn),。
據(jù)此,，研究人員推斷鰻魚科和線鰻科等科魚類擁有共同的深海魚祖先,。研究人員說,，在鰻魚科魚類祖先所棲息的熱帶和亞熱帶，淡水區(qū)域比海洋擁有更豐富的食物和營養(yǎng),。為了保證獲得充足食物和營養(yǎng),，鰻魚科魚類的祖先選擇在淡水中生活,，但產(chǎn)卵場所依然是深海，這一習(xí)慣一直延續(xù)到今天,。（生物谷Bioon.com）
生物谷推薦原始出處：
Biology Letters January 6, 2010, doi: 10.1098/rsbl.2009.0989
Deep-ocean origin of the freshwater eels
Jun G. Inoue1,*, Masaki Miya2,*, Michael J. Miller1, Tetsuya Sado2, Reinhold Hanel3, Kiyotaka Hatooka4, Jun Aoyama1, Yuki Minegishi1, Mutsumi Nishida1 and Katsumi Tsukamoto1
1Ocean Research Institute, The University of Tokyo, Tokyo 164-8639, Japan
2Natural History Museum and Institute, Chiba, Chiba 266-8682, Japan
3Johann Heinrich von Thünen-Institut 22767, Hamburg, Germany
4Osaka Museum of Natural History, Osaka 546-0034, Japan
Of more than 800 species of eels of the order Anguilliformes, only freshwater eels (genus Anguilla with 16 species plus three subspecies) spend most of their lives in freshwater during their catadromous life cycle. Nevertheless, because their spawning areas are located offshore in the open ocean, they migrate back to their specific breeding places in the ocean, often located thousands of kilometres away. The evolutionary origin of such enigmatic behaviour, however, remains elusive because of the uncertain phylogenetic position of freshwater eels within the principally marine anguilliforms. Here, we show strong evidence for a deep oceanic origin of the freshwater eels, based on the phylogenetic analysis of whole mitochondrial genome sequences from 56 species representing all of the 19 anguilliform families. The freshwater eels occupy an apical position within the anguilliforms, forming a highly supported monophyletic group with various oceanic midwater eel species. Moreover, reconstruction of the growth habitats on the resulting tree unequivocally indicates an origination of the freshwater eels from the midwater of the deep ocean. This shows significant concordance with the recent collection of mature adults of the Japanese eel in the upper midwater of the Pacific, suggesting that they have retained their evolutionary origin as a behavioural trait in their spawning areas.
