Elephant nose fish

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

A carnivore that forages over the bottom, sifting loose sand with its chin organ for insect larvae and other small invertebrates. In captivity it takes protein-rich live and frozen foods, with bloodworms the usual staple alongside blackworms, brine shrimp, and tubifex. It generally refuses dry food. Feeding is slow and tentative, so quicker tankmates often grab the food first; offering it after the lights go out gives the fish a fair shot.

Nocturnal feeder; drop food after lights out.

Compatibility

• Generates weak electric pulses from an organ in the tail and reads the returning field to navigate, find food in the dark, and signal to other mormyrids. The chin extension, which is not a true nose, is densely covered in electroreceptors.
• Unusually brain-heavy for a fish. Respirometry found the brain uses close to 60 percent of the animal's oxygen, about three times the highest figure measured in any other vertebrate.
• Sensitive to salt and to many medications, and quick to decline in poor water. Treat conservatively and keep conditions stable.
• Keep one, or keep five or more. Pairs and trios tend to go badly, since one fish dominates and harasses the rest, while a larger group spreads the aggression.
• Nocturnal. It needs dim light and plenty of cover and is rarely active during the day in brightly lit tanks.

Origin and habitat

Gnathonemus petersii is a nocturnal, bottom-feeding member of the family Mormyridae, an old osteoglossiform group whose members both produce and sense weak electric fields. It lives in turbid, slow African rivers over soft beds with submerged wood and leaf litter. Sources differ on the exact range: some references place it in the Niger, Ogun, and upper Chari drainages, while records give a wider Niger-to-Congo distribution. The species name honours the German zoologist Wilhelm Peters. The feature that resembles a trunk is a flexible downward extension of the lower jaw, the Schnauzenorgan, and it carries hundreds of electroreceptors that make it the most sensitive part of the fish's active electrosensory system. An electric organ in the tail puts out brief, weak pulses, and distortions in the returning field let the fish map its surroundings in the dark and find invertebrates buried in sediment. The brain is the standout trait. Respirometry by Nilsson found it consumes close to 60 percent of the animal's total oxygen, roughly three times the highest share recorded in any other vertebrate, a cost tied both to the brain's unusual size and to the fish being cold-blooded. The same study showed the fish holds its oxygen uptake and discharge rate steady down to very low dissolved oxygen, near 0.8 mg per litre.

Breeding

Captive reproduction is almost never achieved in home aquariums, and the fish sold in the trade are wild-caught. Dependable methods for sexing and spawning the species in tanks have not been established.

Common problems

This is an advanced-care species. It reacts badly to salt and to many common aquarium medications, so treatments need to be chosen carefully and dosed conservatively; it is sensitive enough to declining water that it has been used as a living monitor of drinking-water quality in parts of Germany and the United States. Substrate matters more than for most fish. The animal probes loose sand with its chin organ, and sharp gravel can injure those soft mouthparts and stop it feeding, so fine sand is the safe choice. It is nocturnal and shy, and under bright light it tends to retreat and waste away, so dim lighting with ample cover from wood, smooth rock, and low-light plants is important. In a busy community it is easily outcompeted at feeding time and can slowly starve, which is why target feeding after dark works best. Conspecifics are the other problem. In a pair or trio one fish becomes dominant and repeatedly attacks the others, which then avoid it; a single fish or a group of five or more in a large tank both work better than the numbers in between.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size