The Glass Catfish, Kryptopterus bicirrhis (An exceptional photo by Holger Knudsen)

The most transparent known vertebrates are the Asian glass catfish of the genus Kryptopterus.  The two most popular species are Kryptopterus minor, the ghost catfish, and Kryptopterus bicirrhis, commonly known as the glass catfish, which is a mainstay in the tropical aquarium.

Asian glass catfishes live in slow turbid streams throughout Thailand, Malaysia and Indonesia.  They are schooling predators who feed on tiny arthropods, worms, and minnow fry. Camaraderie is important for the little fish—outside of a school, individuals rarely survive (even in an aquarium where all of their other needs are met and they lack predators).  Their remarkable transparency serves as camouflage, hiding them from predator and prey alike.  Growing to a maximum of four inches the catfish live for up to eight years.

A School of Glass Catfish

Asian glass catfish are scaleless and lack pigment, however the cellular dynamics of their transparent tissues are still not fully understood.  In living specimens, the animal’s skeleton is quite visible and its internal organs can be seen with a silver sack.  A viewer with a powerful magnifying glass can watch the fish’s heartbeat and determine the contents of its stomach.  When the catfish dies so does its transparency–after death they turn an opaque white.

The catfish is commercially important for the aquarium trade.  It seems possible that exporters in South East Asia have devised a way to breed the fish en masse, but, if so, it is wholly unknown in the west. The Phantom Glass Catfish is also a major ingredient of some of the salty fish sauces used in Malaysian and Indonesian cooking.