Glass Knife Fish
aka: Green Knifefish, Transparent Knifefish
The Glass Knifefish is very social and will do best in groups of 5 or more. The Glass Knifefish has a peaceful, but sometimes shy demeanor and does best kept in the company of its peers. The Glass Knifefish Eigenmannia virescens are unusual, even for knife fish. The fins and much of the body are transparent and they have a most interesting swimming motion. Their bodies are relatively stiff and they don’t have a dorsal fin, so Its hard to imagine how they can move around so adeptly. When they move they appear to be jet propelled. Its that hard to see anal fin using a rippling motion that provides their means of locomotion. If they are going forward and want to reverse direction, they simply reverse the rippling motion and are moving backward.
This transparent knife fish is a member of the Sternopygidae Family found in tropical South America. As a group they are referred to as Glass knifefish or Rattail Knifefish. There are currently 30 species of glass knifefish grouped into six genera. The Eigenmannia genus has eight described species including E. virescens.
The body is shaped like the blade of a knife, hence the common name of Glass Knifefish. They have a snout that is relatively short rather than the tubular or elongated snout seen on many other types of knifefish, and they have relatively large eyes. Sometimes the body is colored with a very slight green tint, and so it is also called the Green Knifefish.
The Glass Knifefish are non-aggressive and are also quite timid. They do best when kept in a large species tank with their own kind. These are a fish that will do best in groups of 5 or more. They will develop a hierarchy of dominant and submissive fish, but they will not injure each other. They actually communicate using electrical pulses. These are one of the few Knife fish that thrive on the companionship of its own kind and it is an amazing sight seeing these fish together communicating.
Even with a small group however, they can appear to be shy. This is because they are naturally nocturnal so they are not usually active during daylight hours. Make they feel secure by giving them plenty of hiding places with plants and bogwood. Clear acrylic or plastic tubes also work well for hiding places. These fish have poor eyesight so they use electrical impulses as a sort of radar for navigation and locating objects. So even though the tube is clear, their radar tells them that they are in a secure place, but now the aquarist can see them.