TankBud

Elephant knifefish

Rhamphichthys rostratus

Also known as Trumpet knifefish, Ossa knife

FreshwaterFish

Elephant knifefish (Rhamphichthys rostratus)

Care at a glance

Temperature
75–82°F
24–28°C
pH
5.5–7.2
Adult size
39.4 in
100 cm
Minimum tank
238 gal
900 L
Temperament
Mostly peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Diet
Carnivore
Difficulty
Difficult
Breeding
No record
Rarity
Rare
Family
Rhamphichthyidae
Origin
Amazon and Orinoco basins

Overview

The elephant knifefish is a shy, nocturnal and weakly electric giant. It suits only experienced keepers set up for a fish this size.

Did you know

Like its cousin the electric eel, the elephant knifefish generates electricity. It makes only a faint field, which it reads like radar to feel its way and find food in muddy water.

Caring for the elephant knifefish

The elephant knifefish needs public-aquarium space, a tank of 238 gal (900 L) or more. Give it a deep, soft sand bed it cannot scrape its skin on, large smooth caves and dim lighting. These let it feel secure and behave naturally, rather than staying buried and stressed.

Hold the temperature at 75 to 82°F (24 to 28°C), with a slightly acidic to neutral pH of 5.5 to 7.2. A big fish in enclosed water needs strong filtration and steady oxygen, so keep the water very clean.

It spends the day hidden and hunts the bottom at night with its snout. Feed meaty foods after dark, such as earthworms, prawn, mussel and sinking items.

The elephant knifefish is mostly peaceful and rather shy. Despite its calm nature, it will eat fish small enough to swallow, and fast, greedy tank mates easily outcompete it for food. Choose large, gentle companions or keep it alone. It has not been bred in aquaria.

Good to know

Rhamphichthys rostratus is a knifefish of the family Rhamphichthyidae, one of the South American electric knifefishes. Its body is drawn into a long blade, with a curved, tube-like snout. It uses the snout to pick prey from burrows and crevices, and to draw prey out of the substrate. It is also sold as the trumpet knifefish.

In the wild

The elephant knifefish ranges widely through the Amazon and Orinoco basins. It lives over the muddy and sandy floors of large rivers and channels, probing the substrate at night. The water there is warm, soft and dimly lit.

Common questions

What size tank does an elephant knifefish need?

An elephant knifefish needs at least 238 gal (900 L). It spends most of its time in the bottom.

What temperature and pH does an elephant knifefish need?

An elephant knifefish is comfortable at 75–82°F (24–28°C) with a pH of 5.5–7.2.

What does an elephant knifefish eat?

An elephant knifefish eats meaty foods such as earthworms, prawn, mussel and sinking items. Feed it after dark, since it hunts the bottom at night.

How big does an elephant knifefish get?

An adult elephant knifefish reaches about 39.4 in (100 cm).

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