Updated: Mar 25
One of the most fascinating fish I’ve had the pleasure of caring for recently is a species from Africa called Peters' elephantnose fish, Gnathonemus petersii (nath-o-knee-mus pea-ter-see-eye), more commonly referred to as the elephantnose fish.
You can quite easily see where this fish gets its moniker. The long, protruding, trunk-like, mouth adaptation, called the Schnauzenorgan resembles an elephant's trunk. But the curiosities of this species don’t stop there. Equipped with an electrical discharge organ, an enlarged cerebellum, and a unique body shape, this fish can be a fascinating addition to the right aquarium.
G. petersii, was first known to humans as early as ancient Egypt. The many species of elephantfish, Mormyridae (more-mir-id-ee), known as medjed to the ancient Egyptians, were worshiped in the temples of the city of Oxryhynchus, a city named after the sharp-snouted fish. Depictions of these unique fish were found on tomb walls throughout Egypt.
In 1831, Charles Bonaparte, a French naturalist, introduced the elephantfish to western science by describing the family Mormyridae. This family contains over 21 genera and 200 species, including G. petersii. The Mormyridae are found throughout central and western Africa; they vary in diet, behavior, and size. What they have in common is their body shape, electrical discharge organ, and enlarged brain.
Peters' elephantnose fish, Gnathonemus petersii, was first described to western science by British ichthyologist Albert Gunther in 1862. It was probably named after Wilhelm Peters, a German naturalist. The specimen described by Gunther was found in the rivers near Calabar, a port city in southern Nigeria, western Africa (Gunther 1862).
Since then, the elephantnose fish and its cousins in the Mormyridae family have been a focus of research on sensory mechanisms in vertebrates, as well as a common specimen in the aquarium hobby.
In the wild, G. petersii inhabits the turbid, muddy pools of slow-moving rivers. They are active amongst submerged vegetation and downed branches where there is plenty of cover.
In the aquarium, they do well in heavily planted tanks. They like caves or tunnels for protection, and to retreat from the activity of the tank. There are several ways to provide a refuge for your elephantnose.
One way is to purchase a “ghost house”. These are manufactured tubes, some transparent, some opaque, made specifically for elephantfish and knifefish. They are available online or at many local fish stores.
A second method is to stack or build a cave or partially enclosed crevice using the rock and driftwood already present in your tank as decoration. Be sure the cave has no sharp edges, is large enough for the fish to turn around in or has two openings, and is structurally sound so it won’t collapse.
The third method, and perhaps my favorite, provides perfect cover for your fish, while blending seamlessly into your aquarium's natural décor. First, cut a 3 to 6 inch diameter schedule 40 pvc pipe to a length of 12 to 16 inches. Then, smear aquarium-safe clear silicone on the pipe in a thin layer, completely covering the pipe. Next, roll the pipe in a shallow tray with a layer of your desired gravel, sand, or pebble. The substrate should cover the pipe completely, leaving no exposed silicone. You can use the same silicone to attach larger, accent pieces of rock to the pipe as well. Let it rest and set for 48 hours. Finally, place the pipe in the aquarium among the plants, so it blends with your décor. One opening should be nested deep within the aquarium and covered by plants. The other opening can be exposed to the front of the tank for viewing.
G. petersii is carnivorous, and mainly consumes worms, insects, isopods, and crustaceans. It hunts by sifting through the soft sand and soil substrates of its habitat, using its excellent low-light vision, and its electrical discharge organ and the electroreceptors on its specialized mouth organ to locate its prey.
In the aquarium, they will readily consume bloodworms, but will also consume other frozen foods and flake food. If you feed flake food to your elephantnose fish, make sure it is a quality recipe high in animal protein.
The best way to ensure your elephantnose is adequately fed, especially if you have other fish in the aquarium, is to target feed. This method involves using a long baster or syringe to deposit whole frozen food directly in front of the fish, or near where it’s hiding.
The elephantnose fish uses electrical impulses to hunt and has poor eyesight in high-light, but excellent eyesight in low-light. For this reason, target feeding based on the fish “seeing” the food can be unreliable in high light. Consistency is key. Feeding your fish in the same place at the same time every day will ensure its quick discovery of the food.
This is easy with elephantnose fish because of their ability to seamlessly switch between electrolocation and sight. Despite their otherwise unremarkable brain, they are fast learners with long memories (Schumacher 2016).
Electrical Discharge Organ
One of the unique and interesting characteristics of the Mormyridae is their electrical discharge organ. This organ is used to hunt for prey, navigate obstructions, and find potential mates, in the muddy turbid waters which Mormyridae inhabit (Bennett 1971, Caputi et.al. 1998).
The electrical discharge organ is a modified muscle located in the caudal peduncle (tail fin muscles) that uses modified voltage-gated sodium channels to emit a weak electrical discharge. The many electroreceptors located throughout the body and in heavy concentration on the elongated snout portion of the mouth, pick up these charges after they have interacted with the environment and their brain interprets them to give the fish a “visual” of its surroundings. Think of it like echolocation, but with electricity instead of sound (Kramer 1994, Caputi et.al. 1998).
Mormyrids use either a wave or pulse discharge pattern. The wave pattern is a more continuous discharge of electrical signals. G. petersii uses a pulse pattern where there is a significant gap between electrical discharges (Kramer 1994).
Unlike the South American knifefish, Gymnotidae (gym-no-tid-ee), Morymyridae have excellent low-light vision, despite also relying heavily on their electrolocation capabilities.
Their eyes contain a combination of specialized bundles of hundreds of rods and tens of cones, sheathed in a reflective layer called a tapetum lucidum, parabolic mirrors, and photonic crystals. All of these structures together are much more than a way to simply collect as many photons as possible. They provide specific mechanisms in which photons are captured and allowed to be exposed to the photoreceptor cells in the eye as many times as possible (Landsberger et.al. 2008).
To enjoy your captivating elephantnose fish, I recommend dimming your lights to below 50% for a period of time at the beginning or end of the light cycle. They will become more active in these low-light conditions.
There have been no known cases of G. petersii breeding in captivity. Unfortunately, this means commercially available species are still wild-caught. The catching and selling of wild-caught species has negative impacts on the environment and the fish themselves. There is a much higher survival rate when fish are captive bred, as they can be raised and acclimated to desired water parameters.
One theory as to why G. petersii may not breed in captivity is because they are sexually dimorphic (males and females are different) by way of their electrical discharge organs. They identify the sex of other individuals by their electrical discharge pattern. Males have longer signals and females have shorter signals. In captivity, they have been observed switching signal patterns, which confuses individuals as to the sex of other individuals (Landman 1993).
G. petersii have a wide dispersal in the wild. Individuals can be found all over central and western Africa, in freshwater rivers with pH ranging from 6.0 to 8.0, general hardness from 5 to 19 dGH, and a temperature from 71 to 82 degrees Fahrenheit.
In the aquarium, the water parameters can be anywhere within these values. Although the recommended minimum temperature is 77 degrees F. The key is to ensure your chosen parameters remain consistent. It's also best to avoid the extremes on either end of the parameter ranges so if a fluctuation does happen, the values remain in the recommended range.
The most difficult aspect of keeping G. petersii is their susceptibility to fluctuating water parameters. Constant changes in hardness, pH, or temperature can result in elevated stress and a weakened immune system, leaving them open to contracting parasites, or bacterial and fungal infections.
I recommend a tank size of at least 60 to 70 gallons. As these fish inhabit the benthic zone (bottom layer of the aquarium), a shallow, wide, and long tank shape is also recommended. A tall tank with little surface area will not provide enough habitable area for your fish to thrive.
It is not recommended to keep more than one G. petersii in the same tank. They will be territorially aggressive toward one another. If they don’t outright kill each other, the dominant one will subdue the other, causing elevated stress levels and susceptibility to disease. In addition, they will hide most of the time which would be unfortunate, as this species is normally very active in the aquarium, making it an entertaining addition when cared for properly. There have been cases of groups of five or more being kept in the same tank, but you’ll need at least 50 gallons per fish.
More Than A Specimen
Peters' elephantnose fish, or G. petersii as we’ve come to know them, can be more than just another tank inhabitant. The decision to add this fish to your aquarium should not be made lightly. It is crucial to have the correct environment, habitat, water parameters, tank mates, and tank size. Once all these components have been met, then consider why this fish strikes you? There are other fish that have a similar look and behavior that don’t reach 9 inches in length and aren’t aggressive with other members of its species.
For me, G. petersii is an attractive showfish because of their elevated intelligence, ability to switch senses, and their active behavior. Through positive conditioning (treat rewards for desired behavior), you can train your elephantnose fish to feed directly from your hand, or to come to the surface or front of the tank to greet you when you arrive. Over time you’ll notice individuality amongst these fish. Each one will develop a personality with unique behaviors and attitudes, making them a truly interesting addition to the right aquarium.
6.0 - 8.0
5 - 10 dGH
4 - 8 dKH
77 - 82 degrees F
60+ US gallons
Non-aggressive towards other species
Bennett, MVI. (1971) “Electroreception”. Fish physiology, vol 5: Sensory systems and electric organs. Academic Press, New York, London, pp 493-574.
Caputi, A.A., Budelli, R., Grant, K., and Bell, C.C. (1998) “The electrical image in weakly electric fish: physical images of resistive objects in Gnathonemus petersii”. The Journal of Experimental Biology. 201: 2115-2128.
Gunther, Albert. (1862) “Archiv Fur Naturgeschichte”. Berlin: p64.
Kramer, B. (1994) “Communication Behavior and Sensory Mechanisms in Weakly Electric Fishes”. Academic Press, San Diego, pp 233-270.
Landsberger, M., et.al. (2008) “Dim light vision - morphological and functional adaptions of the eye of the mormyrid fish, Gnathonemus petersii”. Journal of Physiology, Paris. 102 (4-6): 291-303.
Landman, R. (1993) “Sex differences in external morphology and electric organ discharges in imported Gnathonemus petersii (Mormyriformes)”. Animal Behavior. 46 (3): 417-429.
Schumacher, S., Burt de Perea, T., Thenert, J., & von der Emde, G. (2016) “Cross-modal object recognition and dynamic weighting of sensory inputs in a fish”. Proc. of the National Academy of Sciences of the U.S.A. 113 (27): 7638-7643.
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