The elephantnose fish lives in murky, dark waters, where seeing its surroundings is virtually impossible. This presents a challenge for avoiding predators and finding prey.
Elephantnose fish have solved this problem by evolving a special elongated chin, which gives them their name. This chin, called a Schnauzenorgan, isn’t just for looks. It actually acts as a specialized electric organ that emits electric signals and generates electric fields.
By generating these fields, the Schnauzenorgan can map out the fish’s surroundings through a process called electrolocation (similar to the way a bat uses sound to detect objects and prey). The electric field interacts with objects in the environment, relaying information to the fish’s skin, which “reads” the map generated by the electric field. When the field contacts an object, it warps. The electrical charge is altered, and sent back to the fish. The charges are interpreted by the many receptors within the fish’s skin, and an image of the environment is formed in the fish’s brain.
The vast number of skin receptors enables the fish to determine not only the shape of an object, but its volume, size, material, and maybe even which direction it’s facing. The elephantnose fish can use the images formed through electrolocation to navigate its environment, avoiding hitting objects as it swims while hunting smaller prey. These images aren’t perfectly clear, but are like someone near-sighted seeing a blurry world when they don’t have their glasses on. This doesn’t affect the fish too much, as basic shapes and patterns are all that are needed to survive and thrive.
This summary was contributed by Thomas McAuley-Biasi.
“Weakly electric fishes generate electrical fields around their bodies by emitting electric signals (electric organ discharges, EODs) with a specialized electric organ.” (von der Emde and Fetz, 2007: 3082)
“In addition, we studied the receptor mosaic of the sensory epithelium, which in the case of G. petersii constitutes almost the entire body surface…”(von der Emde et al., 2008: 280)
“If an object is present near the fish, it causes distortions of the electrical field lines, which change the voltage patterns on the skin of the animal opposite the object. The changed pattern is detected by electroreceptors located all over the fish’s skin.” (von der Emde and Fetz, 2007: 3082)
“Because there is no focusing mechanism, electrical images are always blurred, or “out of focus” and, in this respect, are fundamentally different optical images that are projected onto the retina of a vertebrate eye.” (von der Emde and Fetz, 2007: 3082-3083)
“Prereceptor mechanisms also ensure that the moveable skin appendix of G. petersii, the ‘Schnauzenorgan’, receives an optimal sensory signal during all stages of its movement.” (von der Emde et al., 2008:279)
“Our experiments showed that during active electrolocation, weakly electric fish can do much more than just detect objects and determine their electrical resistance (Lissmann and Machin, 1958). Instead, even in complete darkness, they can perceive parameters such as the volume, size, 3-D shape, contour, material and possibly the orientation of an object.” (von der Emde and Fetz, 2007: 3090)