Pink Knifefish (Orthosternarchus tamandua), Loreto, Peru
Even moderate depths in the Amazon have little to no light…outside of clear water tributaries, at two or three meters, the turbidity of the water has filtered out most of the available light. The Pink Knifefish (Orthosternarchus tamandua) looks a lot like cavefishes with little in the way of pigment and it has only vestigial eyes. The eyes are reduced to a point where they are not functional with regard to deciphering images but can distinguish between light and dark. Some individuals have randomly placed melanophores or pigment spots on their bodies. Looking at the image of the head that I posted here, you can see one of those spots in comparison to the vestigial eye (which is the dark spot to the upper left of the image). Like most knifefishes, this species relies on use of its electrical field to find food, mates, navigate, and otherwise communicate with other individuals.
''Orthosternarchus tamandua'', the tamandua knifefish, is a species of weakly electric knifefish in the family Apteronotidae, native to the deep river channels of the Amazon basin. This species is characterized by its whitish-pink color, long tubular snout, long dorsal appendage, and tiny, bilaterally asymmetrical eyes.