美國地質調查局USGS去年5、6月間在密西西比河上游採樣，2周前科學家竟在北至威斯康辛州Lynxville村附近水域的樣本中，發現外來種亞洲鯉魚的卵，以及即將孵化的晚期胚胎。
亞洲鯉魚現蹤 北至威斯康辛州
肉眼辨識出亞洲鯉魚的卵和晚期胚胎後，科學家開始檢查其他密西西比河水樣本，並發現愛荷華州第19池到密西西比河上游Lynxville村主要水道的第9池間的7個地點，都有亞洲鯉魚卵存在。
Lynxville村位於威斯康辛州南部，密西西比河東岸，在已知的亞洲鯉魚群北方250哩。「這個現象表示亞洲鯉魚產卵的範圍比過去的紀錄更北邊。樣本中出現魚卵顯示確實有產卵行為，但我們不知道蛋是否會孵化和存活，未來是否還會有產卵的行為出現。」USGS中西部區域主任Leon Carl說。
人為引進 外來種恐危害密西西比河生態
「外來種亞洲鯉魚一旦建立了穩固的族群，可能在密西西比河上游造成環境風險和經濟衝擊。需要更深入的研究，以瞭解亞洲鯉魚的棲息地條件和訂定控管措施。」
樣本中的亞洲鯉魚的卵和晚期胚胎，經進一步目視分析其特徵，初步判斷是鳙魚或鰱魚其中一種。USGS進行了基因分析，試圖辨識出確切物種，但結果仍難下定論。基因辨識仍在進行中，預計1至2周內會有結果。
1970年代，為製造水產養殖飼料、控制養殖池和汙水處理池內的藻類數量，鳙魚和鰱魚被引進美國。10年內，這些亞洲鯉魚就逃離且散佈至密西西比河盆地和其他更大的水域。
亞洲鯉魚和原生水生物種直接競爭食物和棲息地。因族群成長太快，擾亂了中西部大河的生態和食物網。
Eggs of invasive Asian carp, including late-stage embryos nearly ready to hatch, were recently identified in samples collected by U.S. Geological Survey scientists in 2013 from the Upper Mississippi River as far north as Lynxville, Wisconsin.
Lynxville is on the east bank of the Mississippi in southern Wisconsin. The eggs and late-stage embryos were 250 river miles upstream of previously known reproductive populations in the river. Spawning would have occurred upstream from this site.
“This discovery means that Asian carp spawned much farther north in the Mississippi than previously recorded,” said Leon Carl, USGS Midwest Regional Director. “The presence of eggs in the samples indicates that spawning occurred, but we do not know if eggs hatched and survived or whether future spawning events would result in live fish.”
“Invasive Asian carp could pose substantial environmental risks and economic impacts to the Upper Mississippi River if they become established,” Carl said. “Further research will help us to better understand their habitat requirements and inform integrated control efforts.”
During the 1970s, bighead and silver carp were imported into the United States for use in aquaculture production of food fishes and biological control of plankton in aquaculture ponds and sewage treatment lagoons. Within 10 years, the carp escaped and spread to the waters of the Mississippi River basin and other large rivers.
The carp are in direct competition with native aquatic species for food and habitat. Their rapid population increase is disrupting the ecology and food web of the large rivers of the Midwest.
The Asian carp eggs and late-stage embryos were discovered two weeks ago while processing samples that were collected in mid-May and mid-June 2013.
Once the scientists visually identified the eggs, they examined other samples taken from the Mississippi River and found Asian carp eggs at seven locations between Pool 19 near Keokuk, Iowa, and Pool 9 of the main channel of the Upper Mississippi River near Lynxville.
The eggs and late-stage embryos were identified as bigheaded carps – either bighead carp or silver carp – through visual analyses of specific features of the eggs and embryos. The USGS attempted genetic analyses to definitively determine which species of Asian carp the eggs belong to, but the results were inconclusive. Genetic confirmation is still underway, with results are expected in one to two weeks.
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