comes close, the fish’s electric field is disrupted. Even a tiny distortion, possibly as small as a microvolt per centimeter (10-6 V/cm) [4], can be detected by the electroreceptors distributed throughout the fish's body, alarming the knifefish. Once the fish detects an object that resembles prey, it will enter a typical attack mode [5, 6]. It will first generate a doublet of high-voltage electric discharges which can cause a powerful involuntary twitch in the hidden prey. The ripples generated can be sensed by the knifefish and reveal the location of the prey. Then the fish will fire a volley of high-voltage pulses to paralyze the prey and then swallow it. To give an even harder shock, the electric eel sometimes seizes their prey in its mouth and curls its body to bring the prey closer to the tail, so that the prey can experience a much stronger electric field [5]. This fascinating ability comes with a mystery: How does a knifefish avoid shocking itself? A theory states that the relatively large size of electric eels (they can reach 2.5 meters in length!) helps them withstand the current that is unbearable to their much smaller prey [7, 8]. Meanwhile, the insulating fat layers surrounding the electric organs [8] and the dissipation of current into water [7] protect the fish’s central nervous system and heart from being directly shocked by the strong current they just produce. Yet, there is indeed much more to be studied and discovered. 在1800年，意大利科學家Alessandro Volta受電 鰻的啟發，創造了第一顆電池 [1, 2]。雖然名字中有個「鰻」 字，但電鰻在分類上並不屬於鰻魚的一種 [2]，儘管兩者外 形非常相似。這些有趣的淡水刀魚擁有獨特的放電能力， 能使其他動物暈眩甚至死亡。到底箇中原理是甚麼呢？ 首先，我們須了解電流這個概念，就是帶電粒子（例如 電子或離子）的流動。兩點之間的電荷差異產生電勢差，當 電路接通時就會導致放電現象，當中電流大小與電路的電 阻成反比。 在生物的神經系統中，信號是以電脈衝的形式傳遞。類 似於電池有正負極，我們的神經元會主動地維持細胞膜兩 邊離子的不同濃度，使細胞內外有著電勢差。透過有秩序 地開關細胞膜中的離子通道，離子就可以順濃度梯度穿越 細胞膜。離子的流動最終產生一波電脈衝，將信息從神經 一端傳遞至另一端。 然而電鰻將生物放電的潛能發揮到極致。牠們身體八 成均由與放電相關的特化器官組成 [3]，這三個器官分別 是石赫氏器官（Sach's organ）、亨特氏器官（Hunter's organ）和主器官（main organ），由稱為「發電細胞」的 特化扁平肌肉細胞組成。這些微小的電池同時以串聯和並 聯方式連接，分別使電壓和電流得以累加。當發電細胞接 收到指示它們放電的神經信號時，細胞膜中的鈉通道會打 開，使鈉離子（Na+）湧入細胞。這使一群群堆疊的發電細 胞內部積聚大量正電荷，將電鰻身體變成一條長長的電池 — 魚的頭部為正極，尾部為負極。這塊「活電池」的電壓可 以高達 600 伏特 [1]，幾乎是香港標準電壓的三倍！
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