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Evolution Of The Elephant Fish

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Elephant fish, (Family: Mormyridae), able to navigate in total darkness, finding food, and distinguishing a mate, all with the help of evolution. Elephant fish, also know as Mormyrid’s, make up a rare family of freshwater fish found in Africa. Over the course of millions of years, a single animal has divided into more than 200 different species.

Perhaps the most dynamic change in the evolution of the fish is the development of an electric organ. Located at the bridge between the fish’s tail, and body, the electrical organ produces a small amount of electrical discharge known as an Electric Organ Discharge (EOD). Elephant fish “see” by way of this discharge, known as electro-location. Electro-location works similarly to a bats echolocation. The electric organ can emit an extremely low voltage, generating a small electrical field that surrounding the fish. Elephant fish are always emitting pulses into their environment electrically. They constantly examine the conductivity of the water surrounding them. The elephant fish can locate animals and objects when variations occur in their electrical field. Any object that enters the electrical field in the surrounding water distorts the electric field and alters the pattern. Electroreceptor’s in the fish’s exterior monitor the electrical field and produces a “presence” of any object near the fish. Not only does this help keep the fish from bumping into anything, elephant fish can distinguish prey from predator, whether it is alive or dead, distance to, and how big the object is, all by using their electrical field.

Along with producing an electric field, the electric organ emits electrical pulses that are used to communicate with other electric fish. Each electrical pulse is emitted in wavelengths, similar to a heartbeat. Every species of Elephant fish produces a slightly different electrical pulse wavelength. These pulses also work to attract a mate. Scientists believe that other electrical fish can understand a separate species electrical pulse, but the species choose to mate only within its own species. Thanks to evolution, these electrical organs have given these fish a chance to survive in a new environment, darkness.

It is believed that after the appearance of the electrical organ, that it still continued evolved to suite the needs of the species. Electric organs have evolved with mechanisms for controlling the fine structure of the fish’s electric discharge waveforms. This allows the fish to produce a stronger wave, and electrical field in less conductive water. This does have some drawbacks. When the fish must constantly emit stronger electrical pulses, the fish is quickly drained of energy. To make up for this, the fish is able to change the number of pulses per minute, second, hour and so on. Doing this presents a major problem. During hours of daylight, the fish would be more susceptible to an attack from other animals. Normally, in the majority of most species, the interval between discharges is very long compared to the duration of discharge itself.

Evolution also left its mark on the elephant fish, specifically, the “elephant” part. The Elephant fish derives its name from the “elephant trunk” which extends from the lower part of the fish’s head. In some species the "trunk" is wobbly, and moveable, while in others it may be held straight out from the head. This slender, snout has been perfectly evolved for detecting and grasping small prey that hides in vegetation or amongst rubble or mud on the base of streams and lakes. At the end of the nose of the fish, there are more than 500 specialized electrical sensor cells which are able to detect the slightest changes in the electrical field caused by small crustaceans under the surface, the fish’s



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