M. GOSWAMI & ANIRBAN ROY RTICLE A EATURE F An understanding of the evolution of the electric organ from muscle cells in electric fi shes can open a new horizon in synthetic biology. Muscles in other vertebrates or invertebrates may be manipulated for generating electrical power in human organs such as heart, brain, and spinal cord. Since the last few decades, the the resting state, the internal potential development and working of electric amounts to -70mV to -80mV (depending organs inside the fi sh’s body has been upon the type of cell). This is termed as a sublime topic of interest for many resting potential or Nernst potential. The researchers. The scientifi c world is of negative sign in the membrane potential the opinion that the electric organs from signifi es the presence of the non-diffusible which electric discharges are produced anions and unequal distribution of ions have evolved half a dozen times in the across cytosol. HILE we humans have to generate environment. Variations of ionic concentration electricity to take care of many W inside and outside the cell as well as activities, there are fi shes that produce difference in the permeability of cell their own electricity. Electric fi shes and Bioelectricity membrane to diverse ions are responsible A fi sh capable of generating electric fi elds Within the aquatic world, there for the existence of resting potential. is said to be electrogenic while a fi sh are hundreds of electric fi shes. Charles Usually K+, Na+, Cl-, Ca2+ ions are that can detect electric fi elds is said to be Darwin had recognised electric fi shes as widely available in the intracellular and electroreceptive. Almost all electrogenic critical examples of convergent evolution. extracellular fl uid. A nerve impulse is fi shes possess the ability to detect The phenomenon where unconnected an electric signal that self-propagates electric fi elds. Teleost freshwater fi shes animals independently evolved parallel along the membrane of a neuron, thus, belonging to orders Mormyriformes and traits to adapt to a particular environment changing the state of resting potential (or Gymnotiformes are both electroreceptive or ecological niche is called convergent resting state). On receiving an adequate and electrogenic whereas fi shes such as evolution. stimulus, the sensory cells induce a nerve sharks are only electroreceptive because Electric fi shes, placed in the orders impulse that carries information signals they cannot produce electricity. Now, Mormyriformes and Gymnotiformes, to brain. The brain again commands back why are some fi shes electrogenic while are usually spotted in the Amazon River response signals through nerve impulse others are not? and its tributaries. Ecologically, Amazon to the muscle cells. Upon reaching a inhabits the world’s most dreadful There exists a striking potential muscle fi bre, the nerve impulse invokes aquatic animals and it is considered that difference between the interior and similar potential changes that are the electric fi shes evolved this signifi cant exterior of most animal cells, including subsequently promoted along the muscle trait to safeguard themselves from being piscine cells. This is more pronounced fi bre, initiating the contraction of muscle killed by such cruel predators. in nerve and muscle cells, where in fi bre. Science Reporter, MAY 2016 38 FEATURE ARTICLE Electrophorus electricus Glass knifefi sh Therefore, electricity serves as an the series connection of electric cells and Electric Organ Discharges imperative tool in the neuromuscular batteries. Electric organ discharges can be widely organization of animals, including fi shes. In most fi shes, the electric organ is categorized into two types: pulse type However, in the course of evolution, restricted to the tail region of the fi sh. In the and wave type. A pulse can be defi ned muscles of certain fi shes lost their ability Electric ray (Torpedo), the electric organ as a single vibration or a concise burst, to contract and those muscles were is located at the proximal head region. whereas a wave means a series of periodic modifi ed for extensive production of The Electric eel (Electrophorus electricus) pulses. Some fi shes liberate short electrical electric potential. These modifi ed muscles carry electric organs along the ventral pulses intermittently whereas some and nerve cells meticulously function in surface of their body. There is a jelly-like others discharge wave-like continuous accordance with the internal physiology subcutaneous electric organ (probably of AC electricity. for creating a bioelectric fi eld. These epidermal origin) in freshwater Electric Based on intensity and effi ciency bioelectric fi elds are more intense than catfi sh (Malapterurus). of EODs, the electric fi shes are classifi ed those produced by normal nerves or Biologists describe the electric output as strongly electric fi shes and weakly muscles. The clusters of such muscles and of this organ as Electric Organ Discharge electric fi shes. Fishes that harvest EODs nerves are called Electric Organs. (EOD), which is mustered because of hefty enough to stun their prey to death continuous ‘triggering’ of electrocytes are called strongly electric fi shes. Electric Electric Organ: Morphology and into the surrounding water. Apart from eel, electric catfi sh, and electric ray are Anatomy producing electricity, electric fi shes can strongly electric fi shes. The electric organ is composed of bunches sense the electric fi eld with a delicate The discharge voltage of strongly of modifi ed, non-contractile muscle fi bres and perceptive sensory organ called electric fi shes ranges from 10 volts to 600 arranged in a stack. This specially designed electroreceptors. volts with a current of 1 ampere depending structure bears electrically excitable cells Underlying in the skin, on the external surroundings. The called electrocytes. Electrocytes receive electroreceptors are employed to detect generation of such high voltage is due to simultaneous command signals from the a small perturbation or slight change in the notably large electric organ containing brain to ‘trigger’ electric discharges. At the electric fi eld created by nearby living numerous electrocytes. The fi sh varies moment of ‘triggering’, the electrocytes and non-living objects. Electric fi shes are, its electric discharge with respect to the are asymmetrically polarized resembling thus, able to locate aquatic animals or any conductance of its habitat (for example, other objects with an electrical salt-water and freshwater have different Torpedo Ray approach where vision is conductances). To enhance the electric deceptive particularly at night power supplied to the surroundings, the or in murky water. impedances (resistances for AC current) of the electric organ and the water must Electric Organs Since the fi shes rely upon be matched, which is called impedance the electricity generated from matching. their electric organs for the purpose of electrolocation, Weakly electric fi sh generate an this process is called active electric discharge whose amplitude electrolocation. On the is less than one volt. They employ contrary, fi shes like sharks EODs for navigation, object can detect unnoticeable preys detection (electrolocation), and deeply buried in sand by means communication with their companions of weak electricity generated (electrocommunication). Peters (Gnathon- by the prey. Since there is emus petersi) and black-ghost knifefi sh no participation of electric (Apteronotus albifrons) are typical Bottom side! organ in the spotting the prey, examples of such fi shes. An incredible Stacked battery-like muscle cells this mechanism is termed as behavior is observed in the male species from electric organ passive electrolocation. of Brachyhypopomus pinnicaudatus (a 39 Science Reporter, MAY 2016 FEATURE ARTICLE Knife fi sh - weakly electric fi sh Electric eel Within the aquatic world, there are hundreds of electric fi shes. The higher frequency fi sh raises its EOD Charles Darwin had recognised electric fi shes as critical examples frequency while the lower frequency fi sh of convergent evolution. lowers its EOD frequency. JAR is a complex phenomenon and nocturnal fi sh), that gives off big, long muscles in the course of evolution. Not a subject of curiosity for contemporary electric hums to charm and allure its mate. only humans, bats also follow the same ichthyologists (fi sh biologists). Among Pulse-type EODs are the principle of electric fi eld generation as higher vertebrates, bats are known to characteristic feature of all strongly these fi shes. employ JAR for electrolocation. Males electric fi shes. However, the EODs of of brown-ghost knifefi sh (Apteronotus weakly electric fi shes can be either of Jamming Avoidance Response leptorhynchus) are territorial in nature and the pulse-type or of wave-type. Species Weakly electric fi shes discharge electricity establish supremacy over other members classifi ed under order Mormyriformes at a fi xed frequency. Every individual fi sh by impounding EOD frequencies. and Gymnotiformes have evolved wave has its own distinct frequency of electric Individuals with highest EOD will discharges and pulse discharges with discharge. When two individual fi shes propose dominion over other fellow complex waveforms. with similar discharge frequencies come members. Behavioural observations on closer at the same time, their EODs tend this fi sh show that instead of performing Evolution of Electric Organ to interfere or superpose with each other JAR, they elevate their frequencies within the jamming range of corresponding rivals Extensive researches led by Michael causing obstruction in electrolocation. during aggressive and confrontational Sussman of the University of Wisconsin- This detrimental interference of two encounters to confi rm their competencies. Madison have recently revealed that all frequencies is called jamming. the six electric fi sh lineages have evolved To prevent jamming, the fi shes shift ‘Exotic’ organisms such as the independently. However, it is found that their frequencies away from one another electric fi sh are one of nature’s wonders they have used the same gene/genetic until they are separated enough for and a ‘gift’ to humanity.