"The elephantnose fish, which finds its way at night using an electrical version of sonar, has sharp enough senses to assess the shape and size of objects in its tank in the dark, researchers have found. The fish can even identify shapes when they are present as simple wire frames rather than solid objects.
The sensing organ of Gnathonemus petersii (which looks, as the name suggests, like an elephant's nose) is actually an elongated chin packed with electrical sensors that detect distortions in the fish's own electric field. As it hunts for food in the pitch darkness of a tropical central African night, the elephantnose fish sweeps its snout over the ground like a person using a metal detector, to navigate around obstacles and locate the larvae it feeds on." (Muers 2007)
"Weakly electric fish can serve as model systems for active sensing because they actively emit electric signals into the environment, which they also perceive with more than 2000 electroreceptor organs (mormyromasts) distributed over almost their entire skin surface. In a process called active electrolocation, animals are able to detect and analyse objects in their environment, which allows them to perceive a detailed electrical picture of their surroundings even in complete darkness. The African mormyrid fish Gnathonemus petersii can not only detect nearby objects, but in addition can perceive other properties such as their distance, their complex electrical impedance, and their three-dimensional shape. Because most of the sensory signals the fish perceive during their nightly activity period are self-produced, evolution has shaped and adapted the mechanisms for signal production, signal perception and signal analysis by the brain. Like in many other sensory systems, so-called prereceptor mechanisms exist, which passively improve the sensory signals in such a way that the signal carrier is optimized for the extraction of relevant sensory information. In G. petersii prereceptor mechanisms include properties of the animal’s skin and internal tissue and the shape of the fish’s body. These lead to a specific design of the signal carrier at different skin regions of the fish, preparing them to perform certain detection tasks. 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.
"Another important aspect of active sensing in G. petersii concerns the locomotor strategies during electrolocation. When foraging, the animals adopt a particular position with the body slanted forward bringing the so-called ‘nasal region’ in a position to examine the environment in front of and at the side of the fish. Simultaneously, the Schnauzenorgan performs rhythmic left–right searching movements. When an object of interest is encountered, the Schnauzenorgan is brought in a twitching movement towards the object and is moved over it for further exploration. The densities of electroreceptor organs is extraordinary high at the Schnauzenorgan and, to a lesser extend, at the nasal region. In these so-called foveal regions, the mormyromasts have a different morphology compared to other parts of the electroreceptive skin. Our results on mormyromast density and morphology, prereceptor mechanisms and electric images, central processing of electroreceptive information, and on behavioural strategies of G. petersii lead us to formulate the hypothesis that these fish possess two separate electric foveae, each of which is specialized for certain perceptional tasks." (von der Emde et al. 2007:3082)
von der Emde, Gerhard; Steffen Fetz. 2007. Distance, shape and more: recognition of object features during active electrolocation in a weakly electric fish. Journal of Experimental Biology. 210(17): 3082-3095.
von der Emde G.; Amey M.; Engelmann J.; Fetz S.; Folde C.; Hollmann M.; Metzen M.; Pusch R. 2008. Active Electrolocation in Gnathonemus petersii: Behaviour, Sensory Performance, and Receptor Systems. Journal of Physiology-Paris. 102(4-6): 279-290.
Mary Muers. 2007. 'Seeing' through the chin. firstname.lastname@example.org [Internet], Accessed August 28, 2007.
Gnathonemus petersii is a demersal species that occurs close to the bottom where it probes for food with the long snout. Territorial and usually aggressive towards members of its own species. This behaviour has been shown to involve electric organ discharge (EOD) activity (Møller 1995). Feeds mostly at night on worms and insects (Mills and Vevers 1989), probably aided by electro-sensory inputs (Møller 1995). The electroreceptors are distributed over the entire head, the dorsal and ventral regions of the body, but absent from the side and the caudal peduncle where the electric organ is located (Møller 1995). Sex-related EOD characteristics in this species has been demonstrated in the laboratory with freshly imported samples during the breeding season; such EOD dimorphism changed with time in captivity (Landsman 1993, 1995). Lead nitrate in water significantly increased EOD rate and selectively altered the EOD waveform of this species (Prabhakar and Landsman 1994). Dubbed a `hearing specialist' having auditory abilities in the range of 100-2500 Hz, with `best frequencies' between 300 and 600 Hz (McCormick and Popper 1984).
Snoeks, J., Tweddle, D., Getahun, A., Lalèyè, P., Paugy, D., Zaiss, R., Fishar, M.R.A & Brooks, E.
This species has a wide distribution, with no known major widespread threats. It is therefore listed as Least Concern. It has also been assessed regionally as Least Concern for central and western Africa.