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Black Widow Tetra

Scientific Name: Gymnocorymbus ternetzi
Family: Characidae, Sub-Family Stethaprioninae

About the Black Widow Tetra

Species Type: Freshwater Fish
Category: Characins

Care Level: Very Easy. Will tolerate a wide range of water parameters including pH, temperature and hardness. Can tolerate higher nitrate levels than other fish and is hardy enough to withstand the cycling process. Will readily eat prepared foods and has no special care requirements.

Origin: Basins of the Rio Paraguay and Rio Guapore, Bolivia to northern Argentina. Found in small slow-flowing creeks and streams, usually with dense overhanging or floating vegetation.

Compatibility/Temperament: Peaceful, especially when kept in groups of at least 6 but preferably more; in smaller groups or individually it may become nippy of fins. Should not be kept with sedate fish such as angelfish, discus, gourami due to likely nipping. In a soft/acidic aquarium, compatible with other characins, dwarf cichlids, rasbora, danio, small catfish and loaches; in basic/alkaline aquaria, suitable companion to livebearers. May be seen chasing each other, but little or no harm is ever done.


A fairly active species when young, it likes some swimming space in a planted aquarium; floating plants are also recommended, along with subdued lighting to bring out the best deep black colouration. As it matures, it becomes less active. It will occupy all levels in the aquarium.

A good fish for the beginning aquarist as it is tolerant of basic water conditions, and quite hardy. Available fish are all captive bred.

Males are slimmer than females, and have a more pointed dorsal and anal fin. Easy to spawn, using the standard methods for characins. Adults will readily devour the eggs if not removed.

Some forms have been selectively bred for aquaria, such as the long-fin and white skirt tetra. Unfortunately, artificially dyed forms (injected with coloured dyes) are sometimes seen; this practice is highly stressful to the fish and results in a much shorter lifespan; such fish should not be purchased.

This species was originally described as Tetragonopterus ternetzi (Boulenger 1895) and was assigned to the present genus by Gomez and Chebez (1996).

The genus Gymnocorymbus was previously considered within the Sub-Family Tetragonopterinae, but this classification has for some time been deemed incertae sedis [Latin for "of uncertain placement"]. In a study published in 2010, it was determined that the Sub-Family Tetragonopterinae should only be used for species within the genus Tetragonopterus. [Robert Javonillo, Luiz R. Malabarba, Stanley H. Weitzman and John R. Burns, "Relationships among major lineages of characid fishes (Teleostei: Ostariophysi: Characiformes), based on molecular sequence data," Molecular Phylogenetics and Evolution, Vol. 54, No. 2 (February 2010)]. Also, J. Marcos Mirande proposed several revisions to the Family Characidae based upon phylogenetic diagnosis in "Weighted parsimony phylogeny of the family Characidae (Teleostei: Characiformes)," Cladistics, Vol. 25, No. 6 (July 2009). Some genera have been moved to a new Sub-Family, while others are now (temporarily) assigned to a specific clade within the Family pending further study.

Black Widow Tetra Diet

Omnivorous, will readily feed on prepared foods such as flake and frozen daphnia and bloodworms.


Grows up to 2.25 inches, some authors suggest up to 3 inches.

Minimum Tank Suggestion

24-30 inches in length.

Ideal water parameters for Black Widow Tetra

Soft to moderately hard (hardness to 30 dGH, preferably below 20 dGH) acidic to basic (pH to 8.0 but preferably under 7) water, temperature 20-26C/68-79F.

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