Miscellaneous Freshwater Fishes
If you have read through the catfishes chapter you will already be aware of Malapterurus electricus (Electric catfish). There are, however, several other fishes that are able to produce electricity. Some use it to find their way around and others for defence and stunning prey, and all are aided by the fact that water is a good conductor. The electric organs are modified muscle cells; those fishes that stun their prey have large, powerful electric organs. Electrophorus electricus (Electric eel) is a good example of this), whereas those which use electricity for navigation have much smaller and less powerful organs. Interestingly electric fishes have very small eyes and inhabit silty waters with poor visibility where electro navigation is an asset.
A word of caution: THESE FISHES ARE NOT FOR BEGINNERS. Electric eels can deliver a shock of more than 500 volts and that is powerful enough to stun a horse. Even though you may fancy keeping one for its novelty value, please give the matter very careful consideration before proceeding. They are powerful creatures that require specialist handling, and if you have young children who may put their hands in the aquarium, do not even think about it.
Members of the African genus Mormyridae (Elephant noses fish) use electric pulses to find their way around, communicate with each other, and passively defend territory. The electric organ is small, weak, and situated near the caudal peduncle. These fishes are so sensitive to water quality that in Germany they have been introduced into a water supply to monitor drinking water purity; if their electrical pulses increase from the normal 800 per minute this indicates a deterioration in the water purity.
In the aquarium the most commonly kept species is Gnathonemus petersi (Peter’s elephant nose). If your aquarium has been established for a year or more, everything is going well, and it is not overstocked, you could try to keep one or two elephant noses. They are quite peaceful but if you are intending to keep more than one, make sure they are of similar size, as large specimens will sometimes bully smaller, weaker ones.
Elephant noses are nocturnal so ensure that there are caves or other suitable places for them to hide in during the day. If you are keeping more than one specimen it is important that the fishes can hide away in separate areas of the aquarium so that their electric fields are not permanently interacting with each other.
Feed them in the evening, offering flake, frozen, and live foods. They are particularly fond of frozen bloodworm. They use their soft “snout” to detect food in the substrate, and this organ can easily be damaged by sharp gravel, so fine sand is more suitable.
As we have already stated, they are sensitive to poor water conditions. In the aquarium regular partial water changes (with aged or conditioned water) are advantageous.
Another species of weakly electric fish, this time from South America, is Apteronotus albifrons (Ghost knife fish) whose common name stems from tribespeople in Guyana who believe it to be inhabited by a ghost or evil spirit. This fish grows large, up to 50 cm (20 in), much too big for a community aquarium. It is mentioned here because it too has a weak electric organ near the caudal peduncle which it uses to locate food. Should you wish to keep it, do remember they can sometimes be aggressive. They need a furnished aquarium with plenty of hiding places and will even tolerate larger peaceful companions once they have become used to aquarium life. Feeding these fishes poses little difficulty as they are omnivores, taking everything from pieces of meat to tablet foods.