March 10, 2017 by Mary Carol Garrity
After its discovery almost 40 years ago, a very small and eyeless species of catfish now has an official name courtesy of two scientists from Academy of Natural Sciences of Drexel University.
John Lundberg and Tiago Carvalho named the catfish Micromyzon orinoco after the Orinoco River, where the fish was originally discovered during the US-Venezuelan Orinoco Delta Expeditions of 1978 and 1979.
Before scientists could give this species a proper name, they had to do an examination of the specimen and a comparison to existing catfish.
This proved to be difficult as only two specimens of M. orinoco have ever been documented, both of which are currently being held at the Academy of Natural Sciences as a part of the ichthyology collection.
These catfish are particularly elusive because of their tiny size, only about 15 millimeters long, and their habitat at the bottom of very deep and poorly sampled South American rivers.
“There is no way to encounter these fish other than by trawling with fine, mesh netting. They are out of reach in lightless, swift-flowing river channels … and they probably bury themselves in sand much of the time,” Lundberg said.
M. orinoco lives in deep and dark waters and has no eyes. It also has almost no pigment, making it nearly colorless in appearance. There are two evolutionary explanations as to why this species is eyeless.
“True eyes are expensive to make and maintain, in terms of energy. And these animals are not in a highly productive habitat with unlimited food resources. … Second, eyes without eyelids are potentially a liability in a world of shifting sand where there is no light anyway,” Lundberg explained.
Other fish living in the same habitat as M. orinoco also have similar adaptations, including lack of eyes and pigment, small and flattened bodies, and sensory specializations.
The genus in which this catfish belongs, Micromyzon, is a part of the Aspredinidae family which contains 45 different species of diverse South American catfish.
The genus, however, only has one other species, M. akamai, discovered by Lundberg and fellow scientist John Friel in 1993. Both catfish are classified in this particular genus due to five shared characteristics including their small body size, unique body armour and expanded lateral-line ossicles, bones that connect the auditory system of the fish from swim bladder to inner ear.
In the future, the specimen may help scientists identify and classify new species more quickly and easily.