TankBud

Sand knifefish

Gymnorhamphichthys rondoni

Also known as Rondon's sand knifefish, Mousetail knifefish, Thermometer knife

FreshwaterFish

Sand knifefish (Gymnorhamphichthys rondoni)

Care at a glance

Temperature
75–82°F
24–28°C
pH
5.5–7.2
Adult size
5.9 in
15 cm
Minimum tank
53 gal
200 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 sand beaches

Overview

The sand knifefish is a slender, shy knifefish for a dim tank with a deep sand bed. It is a fish for experienced keepers.

Did you know

The sand knifefish leads a double life tied to the clock. It stays buried out of sight in the riverbed sand all day, then rises at night to swim and hunt across that same sand.

Caring for the sand knifefish

The single most important thing for a sand knifefish is a deep layer of soft, fine sand with no sharp grains, kept clean. It needs a bed it can burrow into, in a tank of 53 gal (200 L) or more. Add dim light, gentle flow, calm surroundings and some wood or leaf litter for extra cover.

Keep the water at 75 to 82°F (24 to 28°C), soft and slightly acidic to neutral, at a pH of 5.5 to 7.2. Feed small meaty foods after dark, such as micro worms, frozen bloodworm and other fine sinking items. Drop the food where it forages.

The sand knifefish is mostly peaceful and can be kept singly or as a pair. It is shy and slow at feeding, so avoid boisterous tank mates that will strip the food before it surfaces. Small, very gentle fish are safest, and anything tiny enough to swallow is at risk. Breeding is not recorded in the aquarium.

Good to know

Gymnorhamphichthys rondoni is a small sand knifefish in the family Rhamphichthyidae, with a translucent, banded body and a long, slender snout. It is weakly electric, like the rest of its family, and uses that sense along with its snout to find food buried in sand. The banded pattern is the source of its nickname, thermometer knifefish. Fish in the trade are wild caught.

In the wild

The sand knifefish lives along the sandy beaches and bars of the Amazon and Orinoco. There the bottom is clean, fine sand it can burrow straight into.

Common questions

What size tank does a sand knifefish need?

A sand knifefish needs at least 53 gal (200 L). It spends most of its time in the bottom.

What temperature and pH does a sand knifefish need?

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

What does a sand knifefish eat?

A sand knifefish eats small meaty foods such as micro worms, frozen bloodworm and other fine sinking items. Feed it after dark, dropping the food where it forages.

How big does a sand knifefish get?

An adult sand knifefish reaches about 5.9 in (15 cm).

Related species