The Small mouth electric catfish Malapterus microstoma.

 

​As humans, we tend to think that animals sense their world through the use of sight, smell, taste, touch and sound – and until recently we couldn’t appreciate the possibility of any animal using other means of sensing their environment.

​Now, the relatively recent development of specialised equipment has allowed us to begin to detect the presence of minute electrical charges in the environment and has enabled us to appreciate the importance of producing and receiving electrical charges within a range of fish species.

​Now, the relatively recent development of specialised equipment has allowed us to begin to detect the presence of minute electrical charges in the environment and has enabled us to appreciate the importance of producing and receiving electrical charges within a range of fish species.

​Quite a shock...

​Historically, our appreciation of fish using electricity has been limited to the small number of fish that are capable of producing a potentially lethal electrical charge.

​The Electric catfish Malapterus electricus, capable of producing a charge of up to 350 volts, was featured in Egyptian hieroglyphics as early as 2750 BC, and its formidable reputation is reflected when its name is translated from Arabic as meaning ‘father of thunder’.

​The flesh of the fish was even thought to confer an inner strength or power on those who ate it and became a popular dish. I suspect that the job of catching or preparing the dish was not quite as popular.

​The Romans were a little more subtle in their appreciation of electrical fish and used the 220 volts produced by the electric ray Torpedo torpedo as an early form of electrotherapy.

​The indigenous people of South America would drive large animals towards the haunt of the most powerful producer of electricity among fish, the Electric eel Electrophorus electricus.

​Any animal that fell into the lair of this formidable fish could provoke it into releasing a lethal charge of up to 650 volts.

Credit: Scotcat

​Current challenge

​Despite, or even because of, the formidable reputation and potentially dangerous capability of these fish, many fishkeepers will enjoy the challenge of keeping these fish within an aquarium.

​As a child, I remember being literally thrown across the room by the blast of an electric catfish that I had bought and smuggled into my home aquarium.

​Today, the sale of these fish is restricted to a small number of specialist suppliers who are prepared to ensure that any potential keepers are fully aware of the unusual ‘challenges’ of keeping this species.

​Electricity generation

​Those fish that are capable of producing electrical currents can be classified as either ‘strong’ electric fish or ‘weak’ electric fish.

​The ‘strong’ electric fish, such as the Electric eel, the Electric ray, the Electric catfish and the Stargazer Uranoscopus appear to use electricity to stun their prey and to discourage intruders or predators.

​Most of these fish exhibit the classical ‘sit and wait’ approach of an ambusher, stunning their prey as they approach within a safe striking distance.

​The ‘weak’ electric fish, such as the Mormyridae (elephant fish), the Gymnarchidae (knife fish) and the Rajidae (ray), appear to use the production of electricity as an aid to location or communication.

​The electrical charge is produced in specialised electrical organs. Each of these organs consists of stacks or bundles of specialised cells, known as electrocytes, and the location of these specialised organs will vary with the species of fish.

​The Electric eel has three separate electricity-generating organs that run along the length of its body, with the main organ consisting of over 100,000 electrocytes. Weakly electric fish tend to have one or more organs along each side of the caudal peduncle.

​The ability of fish to generate their own electrical fields is not only limited to those fish which possess the specialised muscle structures. A number of normal physiological processes appear to be responsible for producing a range of small electrical currents. A minute electrical charge is produced each time a muscle is contracted.

In fact, the effective function of most membranes within a fish relies upon a minute electrical charge being generated across their surface. Therefore each time a fish opens its gill cover to breathe, it will generate a minute electrical charge.

Even when a fish is wounded, the fact that a number of internal membranes are exposed will generate a weak electrical field.

credit: planet catfish

​Reception of electricity

​While the production of electrical currents associated with those fish such as the Electric eel or Electric ray has long been recognised, the importance and role of receiving electrical impulses ('electroreception') is an area that has only been able to be studied since the development of relatively sensitive detection equipment.

​The reception of electrical fields can be classified into those that are naturally present within the aquatic environment (abiotic fields) and those that are produced by the fish themselves (biotic fields).

​Although many freshwater and marine fish are electroreceptive, the most important exception to this particular sense is found within the bony fishes or teleosts.

​The teleosts, when based on sheer numbers and individuals, represent the majority of fish that are found within the aquatics industry.

​According to Nelson (1994), the group contains 42 orders, 431 families and 23,681 species. However, the ability to receive electrical signals has independently evolved within four teleost groups that the fishkeeper may come across, including the African Mormyriformes (elephant fish), the South American Gymnotiformes (knifefish and electric eels) and the Siluriformes (catfish).

​The abiotic, low frequency magnetic fields produced by natural seismographic or geochemical processes of the earth appear to be used as electrical landmarks by a number of fish.

​Sharks and rays appear to have the ability to generate their own 'internal compass' by measuring the minute changes in electrical fields that are produced by swimming through these natural electrical fields.

​Small magnetic particles have even been found in the snout of Yellowfin tuna and the lateral line of Atlantic salmon.

​These minute particles have been identified as a means by which these long distance migrators may use the earth's weak magnetic field to navigate across the expanses of the large oceans.

​Dogfish and rays have been shown to use electroreception to detect weak electric signals emitted by the muscle contraction associated with their prey, even when they are buried under several cm. of sand.

​Active male Stingrays have even been observed as detecting receptive females by the weak electrical field emitted by the rhythmic opening of the female's spiracles.

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