Fish, Tanks and Ponds

Fish, Tanks and Ponds
A comprehensive guide to fish

Sternopygus macrurus

Long tail knifefish

Long tail knifefish, Sternopygus macrurusLong tail knifefish, Sternopygus macrurus
Photos by Andy Rapson


Sternopygus: Greek, sternon = sternon, + Greek, pyge = tail

General Notes:

Sternopygus macrurus is a large and aggressive fish which should be housed alone. Sternopygus macrurus is quite secretive and seems to prefer to remain out of site during the day time by lying up very close to or under bog wood or branches. The fish probably feeds mostly after lights out.


In the wild Sternopygus macrurus feeds mainly on aquatic aquatic insect larva, crustaceans and terrestrial insects. The stomach contents of wild fish have been found to contain fish scales and some plant material. In captivity Sternopygus macrurus is unlikely to accept anything other than live food.


There are no visible differences between the sexes but Sternopygus macrurus is an electrogenic species and there are difference between the electric fields that males and females emit.


Sternopygus macrurus hasn't been bred in captivity. In the wild this fish breeds at the beginning or during the rainy season. The male will defend a territory and try to attract nearby or passing females with an electrical signal. Up to 6000 eggs are laid at one time and these are watched over by the male. The fry become free swimming and begin feeding at seven days old.

Wild status

The health of the wild population of Sternopygus macrurus has not been evaluated.

Information at a glance

pH: 6 - 6.5
dGH: 4 - 15
Temperature: 22 - 28°C (72 - 82°F)
Diet: Carnivore
Size: 141cm (56in)
Min tank size: 2400 litres
Difficulty level: Difficult
Aquarium type: Keep alone
Swimming level: All levels

Distribution and habitat

distribution map for Long tail knifefish, Sternopygus macrurus

Origin: South America: Amazon and Orinoco River basins

Habitat: Lives in swamps, streams, and rivers with still or sluggish waters.


Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Gymnotiformes
Family: Sternopygidae
Genus: Sternopygus
Species: S. macrurus (Bloch & Schneider)

Common name:
Long tail knifefish

Synonyms: Gymnotus macrurus, Hildatia brasiliensis, Sternopygus marcgravii.