創(chuàng)作內容
閃電會打死魚嗎?Conventional wisdom says to get out of the water when a storm approaches. However, while people are scrambling for shore, the fish and whales of the sea stay right in the water. Considering sea creatures still exist in the ocean it would seem they are unaffected by lightning. This is only mostly true and a look at how lightning and the ocean work will explain whether or not lightning strikes kill fish.傳統(tǒng)的觀念告訴我們如果風暴靠近時要遠離水體. 人們可以爭相上岸但是海中的魚跟鯨豚只能留在水中. 從海洋生物還能生存下去這點來看他們沒有受到閃電的影響. 這種說法很可能是對的, 我們來看一下閃電跟海洋是怎麼在雷擊時作用的, 這可以解釋閃電會不會打死魚.How Often Does Lightning Hit the Ocean?閃電常會打到海面上嗎?Fortunately for fish, lightning does not often strike the ocean, relatively speaking. NASA uses satellites to track storms and lightning around the world and reports in its December 2001 article “Where Lightning Strikes” how Florida and Central Africa are more likely to get hit than the open ocean. One of water’s special properties is its high heat capacity, which means air above the ocean won’t heat as much as air above land. Since hot low-lying air is necessary for thunderclouds to form, the open ocean doesn’t see too much lightning. Hurricanes of course do form over the ocean however these storms rarely have lightning, reports NASA in "Electric Hurricanes".對魚來說真是慶幸, 相對來說閃電並不常擊中海洋. NASA使用衛(wèi)星追蹤全世界的風暴跟閃電之後在2001年的 " 閃電會擊中哪兒" 的報告書說明佛羅里達跟中非洲比開放性的大洋更容易遭到雷擊. 原因之一是水本身有極高的熱容量, 意思是說在海洋上的空氣會比在陸地上的加熱慢. 由於底層有熱空氣是閃電雲(yún)形成的必要條件, 所以在開放性的大洋不太常看到閃電. 當然了, 颶風/風暴/颱風是從海洋上形成但是這些風暴很少帶有閃電, NASA在 "閃電風暴" 的這報告書中如此說道.What Happens When Lightning Strikes the Ocean?那如果閃電打到海上會怎樣?Although lightning is less likely to strike the ocean, these bolts of electricity do on occasion make it to sea. As lightning hits the ocean the electric current spreads along the surface of the water, rather than downward says April Holladay in her March 5, 2004 USA Today “Wonder Quest”. Since the lightning bolt does not continue down into the depths of the ocean it is less likely to affect fish. However, people on the surface can be affected. Holladay goes on to quote National Severe Storms Laboratory (NSSL) scientist David Schultz as saying lightning strikes have killed people at the ocean’s surface more than 30 yards from the hit. This is due to how water conducts electricity.即使閃電很少打中海洋, 這些電流偶然還是會打到海上的. 當閃電擊中海洋時電流會延著表面散布開來, 而不是像在April Holladay在2004年3月5日的USA Today "Wonder Quest" 專欄所說的往下打. 因為閃電不會在海洋繼續(xù)往下延伸所以這不太可能影響到魚類. 然而停留在海面上的人類就有可能受到影響. Holladay 所引用的 Nationa Server Storms Laboratory (NSSL) 的科學家 David Schultz 說雷擊點30碼半徑內會殺死人, 這要視水的導電性而定.Why Doesn't Lightning Strike Deeper into the Ocean?那為什麼閃電不會深深打進海洋?Lightning spreads across the surface of the ocean due to a phenomenon called the skin effect which simply refers to an electric current's tendency to stay at the surface of a conductor. Meanwhile, skin depth refers to how deeply an electric current can penetrate a conductor. Richard Fitzpatrick, a professor of physics at the University of Texas at Austin, explains on his page "Propagation in a conductor" how in good conductors skin depth decreases as wave frequency increases. Salt water is a good conductor, so when lightning hits it has a fairly low skin depth.閃電會在海洋的表面散布開來是因為一種叫做 "集膚效應" 的現(xiàn)象, 意思是說電流會傾向在導體的表層流動. 而這個集膚的厚度要看電流容不容易穿過導體而定. 德州大學的物理教授 Richard Fitzpatrick在他的文章 " 在導體中的傳送 " 說明了當頻率提高時在良導體中的集膚深度會降低, 鹽水是良導體, 所以閃電擊中時它的集膚深度相當?shù)販\.Do Fish Die From Lightning Strikes?所以魚會被閃電打死?Since lightning tends to spread along the surface of the ocean, where humans swim, it’s best for people to leave the water. Fish are generally found deeper in the ocean where the electric current is less likely to catch them, however a fish unfortunate enough to be at the surface close to a lightning bolt would most certainly be fried. NOAA’s National Severe Storms Laboratory notes in its “About Lightning…FAQ” page that lightning can penetrate a short distance into the water and kill fish nearby. Martin Uman of the University of Florida’s electrical and engineering department says the danger zone for fish is 10 to 20 feet down, as referenced in the MSN Encarta column “Martha Talks Back” by Martha Brockenborough. Ultimately, the answer to the question “Does lightning kill fish?” is – occasionally, but not often.因為閃電傾向在海洋的表面散布, 就是指人們在游泳的那層, 所以人們最好離開水體. 魚兒通常會停留在閃電電流接觸不到的深度, 但是如果有隻不幸的魚靠近到雷擊的海面表層那它當然就會被炸熟了. NOAA的國家強烈風暴實驗室在它的 "關於閃電" FAQ頁面中指出閃電可能穿透短短的距離然後殺死附近的魚. 佛羅里達大學電機系的 Martin Uman 說對魚來講所謂的危險區(qū)是10~20呎深. 在微軟的 MSN Encarta 數(shù)位多媒體百科全書中 Martha Brockenborough 在她的 " Martha Talks Back " 專欄中引用了這段話. 總結來說這個 "閃電會打死魚嗎" 問題的答案是: 偶而會打死, 但是不常見.
看到這邊對電魚有了初步的瞭解, 可惜 wiki 沒有提到它的電耐性/承受度. 所以再次搜尋網路, 找到了這個:An electric fish is a fish that can generate electric fields. A fish that can generate electric fields is said to beelectrogenic while a fish that has the ability to detect electric fields is said to be electroreceptive. Most electrogenic fish are also electroreceptive.[1] Electric fish species can be found both in the ocean and in freshwater rivers of South America (Gymnotiformes) and Africa (Mormyridae). Many fish such as sharks,rays and catfishes can detect electric fields and are thus electroreceptive, but they are not classified as electric fish because they cannot generate electricity. Most common bony fish (teleosts), including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.電魚是指會產生電場的魚類. 能夠製造出電場的魚稱作 beelectrogenic (可生體發(fā)電), 另外如果這種魚能夠偵測電場則叫做 electroreceptive (可感應電的). 大部份的生體發(fā)電魚也可以感應到電. 電魚的品種從海中到像是南美洲( Gymnotiformes )跟非洲( Mormyridae )的淡水河中都有發(fā)現(xiàn). 許多魚像是鯊魚, 鰩魚跟鯰魚可以偵測到電場因而歸類成 electroreceptive (可感應電的), 但是牠們因為無法發(fā)電之故所以不歸類到電魚之中. 大部份的硬骨魚( teleosts ;包括在水族館中看得到的大多數(shù)魚跟食用魚)都無法感應電或生體發(fā)電.Strongly and weakly electric fish 強電魚以及弱電魚Electric fish produce their electrical fields from a specialized structure called an electric organ. This is made up of modified muscle or nerve cells, which became specialized for producing bioelectric fields stronger than those that normal nerves or muscles produce (Albert and Crampton, 2006). Typically this organ is located in the tail of the electric fish. The electrical output of the organ is called the electric organ discharge (EOD).電魚使用牠們身上一種叫做電力器官的特化組織來產生電場. 這是由特化過的肌肉或者神經細胞所組成來製造出比一般的神經/肌肉電流強得多的生物電場( Albert and Crampton, 2006). 基本上這器官位於電魚的尾部. 這種由器官產生的電力叫做生物器官放電(EOD).Fish with an EOD that is powerful enough to stun prey are called strongly electric fish. The amplitude of the signal can range from 10 to 600 Volts with a current of up to 1 Ampere. Typical examples are the electric eel(Electrophorus electricus; not a true eel but a knifefish), the electric catfishes (family Malapteruridae), and electric rays (order Torpediniformes). Strongly electric marine fish deliver low voltage, high current electric discharges while freshwater fish have high voltage, low current discharges. This is because of the different conductances of salt and fresh water. To maximize the power delivered to the surroundings, the impedances of the electric organand the water must be matched. In salt water, a small voltage can drive a large current limited by the internal resistance of the electric organ. Hence, the electric organ consists of many electrocytes in parallel. In freshwater, the power is limited by the voltage needed to drive the current through the large resistance of the medium. Hence, these fish have numerous cells in series.[2]具有生物器官放電的魚如果其電力強度足以電暈要抓的獵物叫做強電魚. 其訊號振幅範圍從 10 到 600 伏特, 電流強度可上至一安培. 典型的例子就是電鰻 (Malapteruridae 科)跟電鰩魚 (Torpediniformes 目). 海棲的強電魚使用低電壓高電流的放電, 淡水的強電魚則使用高電壓低電流的放電. 這是因為鹽水跟淡水有不同的導電率所致. 如果希望傳導出去的電威力最大化那麼放電器官的抗阻必需配合水體. 在鹽水中只要用低壓就能驅動大電流, 這電流受限於魚內部的發(fā)電器官的內部抗阻, 因此其內的發(fā)電細胞會以並列方式來組成. 在淡水中電流的威力受限於電流要通過的導體抗阻所需電壓而定, 所以淡水魚的發(fā)電細胞以串列組成.By contrast, weakly electric fish generate a discharge that is typically less than one volt in amplitude. These are too weak to stun prey and instead are used for navigation, object detection (electrolocation) and communication with other electric fish (electrocommunication). Two of the best-known and most-studied examples are Peters' elephantnose fish (Gnathonemus petersi) and the black ghost knifefish (Apteronotus albifrons).對比之下弱電魚放出的電基本上低於一伏特, 這個太弱了不足以電暈獵物所以是用來偵測獵物的 ( electrolocation 電力定位), 以及用來跟別的電魚溝通( electrocommunication 電力傳達通訊). 最知名且最常被研究的例子是彼氏錐頜象鼻魚跟黑色鬼刀魚.The EOD waveform takes two general forms depending on the species. In some species the waveform is continuous and almost sinusoidal (for example the genera Apteronotus, Eigenmannia and Gymnarchus) and these are said to have a wave-type EOD. In other species, the EOD waveform consists of brief pulses separated by longer gaps (for example Gnathonemus, Gymnotus, Raja) and these are said to have a pulse-type EOD.這種生物放電的波形有兩種, 視魚種不同而定. 某些品種的波形是連續(xù)的而且近乎正弦波, 比方說是無背魚科( Apteronotus ), 艾氏鯷科( Eigenmannia) 跟裸臀魚科( Gymnarchus )就被稱為波形放電. 其它種類的生物放電則是使用較長間隔的短脈衝型態(tài),比方說是錐頜象鼻魚屬( Gnathonemus), 裸背魚科( Gymnotus )跟鰩科,就是使用稱為脈衝形放電的生物電流.
電鰻如何發(fā)電？為什麼不會電到自己？
烏拉圭蒙特維多市克勒門特伊斯特柏生物學研究所的整合暨計算神經科學部主任兼資深科學家卡布提（Angel Caputi）回答：
翻譯／陳儀蓁
電鰻之所以能產生大量電流，靠的是高度特化的神經系統(tǒng)，它能使特化電力器官中的圓盤狀發(fā)電細胞同步活化。這個神經系統(tǒng)利用一個指令核心，命令電力器官開火；複雜的神經序列會在瞬間活化上千個細胞。喔, 看到這邊可以知到電魚其本身的電耐性沒有想像中的好, 所以說如果這些電魚所在位置是雷擊區(qū)那也是被電死. 不過你先想想這些電魚的生存環(huán)境大部份都是底棲的, 不然就是雨林沼澤區(qū), 所以說牠們真正被閃電擊中而掛點的機率其實非常地小.每一個發(fā)電細胞外所攜帶的負電荷，與細胞內相差了將近100微伏特。當命令訊號到達的時候，神經末稍會釋放出微量的乙醯膽鹼（一種神經傳遞物）。這個釋放動作會使發(fā)電細胞的細胞膜上，開啟一個電阻較低的臨時途徑，連接了細胞內與細胞外。如此一來，每個細胞就像電池一樣，活化的一邊帶著負電荷，而另一邊則帶著正電荷。由於細胞在電力器官中的排列方向都相同，就好比手電筒中成串的電池，因此已活化細胞所產生的電流，會「電擊」鄰近任何一個尚未活化的細胞，並在短短大約兩毫秒內形成串聯(lián)。如果電鰻是棲息在空氣中的話，產生的電流將高達一安培，而且自身也將變成一個電壓500伏特的電池；然而水提供了其他出口，因此降低了電流強度。至於為什麼電鰻可以電擊其他動物，而不會電到自己，一種說法是，電擊的強度取決於電流通過生物體任何特定區(qū)域的流量和時間。為了方便比較，我們可以將電鰻的身體比做成年男性的手臂，兩者粗細相當。要使這樣一條手臂的肌肉產生痙攣，以200毫安培的電流來說，必須持續(xù)50毫秒。但電鰻發(fā)出的電流比這個數(shù)字要少得多，而且只會持續(xù)2毫秒。另外，電鰻所產生的電流，有很大一部份會透過表皮消失在水中；而進入小型獵物體內的電流在比例上則強得多。舉例來說，長度是電鰻1/10的獵物，體積將只有電鰻的1/1000，因此遭到電擊的是電鰻身旁的小動物，而不是電鰻自己。
Ever Quest 2 (32)