Aquarist Atlas
Aquarist Atlas · tetras & characins

Tetras

The tetras are the small, schooling characins that fill the soft, tea-dark waters of two continents. The true tetras (Characidae) — Paracheirodon, Hyphessobrycon, Hemigrammus, Nematobrycon and a thousand more — radiate across the Amazon, Orinoco and the rivers of the Guianas, where blackwater chemistry and seasonal flood have produced a staggering diversity of jewel-bright fishes. Alongside them swim the pencilfishes (Lebiasinidae), the gliding hatchetfishes (Gasteropelecidae), the slender Iguanodectidae, and an entire parallel radiation in Africa — the alestid tetras (Alestidae), from the shimmering Congo tetra to the tigerfish. This section is an atlas of all of them, built to the same standard as the cichlid, cory and pleco pages: researched, cited species accounts with no Wikipedia and no invented facts.

© Adobe Stock

Most tetras are fishes of specific water — the acidic, mineral-poor blackwater of a flooded Amazon igapó, the clearwater of a Guianan creek, the white-sand streams of the Río Negro, a Congo rapids. Soft, often warm and tannin-stained, these waters shaped their colour and behaviour, and reading where a species comes from is the foundation of keeping it well. Each species page records the water it was drawn from.

A dense shoal of small tetras schooling together over a dark substrate
Tetras are shoaling fish — kept in numbers they hold a tight school, and the colour and confidence of the whole group lift when there are enough of them.
Close view of a neon-type tetra with an electric blue lateral stripe and red belly
The neon stripe is structural colour — light scattering off stacked guanine platelets in the skin, not pigment — which is why it flares and dims with the angle of the light.
A tannin-stained blackwater stream with submerged leaf litter and roots
Blackwater is the tetra heartland: acidic, soft and the colour of weak tea, stained by tannins leaching from a deep bed of drowned leaves and wood.

Photos © Adobe Stock

1,450 species in the atlas

This section covers the tetras across five characiform families — Characidae, Lebiasinidae, Gasteropelecidae, Iguanodectidae and the African Alestidae — following the Catalog of Fishes and FishBase for valid names. Characidae alone runs to well over a thousand species and is still growing as Amazonian and African drainages are surveyed; new accounts are added as the atlas fills in.

Species

1,450 of 1,450 species

Characidae · 1214

The true tetras — the great Neotropical radiation, taken here in the traditional broad sense. It holds the neons and cardinals (Paracheirodon), Hyphessobrycon, Hemigrammus, Moenkhausia and the rest of the aquarium favourites, as well as the glandulocaudine “false tetras” (Corynopoma, Mimagoniates) — lineages that recent classifications split into Acestrorhamphidae and Stevardiidae.

Iguanodectidae · 32

Slender, fast mid-water characins — Iguanodectes and the Bryconops “glass tetras” of the Amazon and the Guianas.

Lebiasinidae · 75

The pencilfishes and splash tetras — peaceful Nannostomus, Copella and Pyrrhulina of Amazonian blackwater, some of which spawn on leaves above the surface.

Gasteropelecidae · 9

The freshwater hatchetfishes — deep-chested surface fish (Carnegiella, Gasteropelecus, Thoracocharax) whose enlarged pectoral muscles let them skitter clear of the water.

Alestidae · 120

The African tetras — a parallel radiation on the other side of the Atlantic, from the iridescent Congo tetra (Phenacogrammus) and schooling Brycinus to the predatory tigerfishes (Hydrocynus).

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