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Serpae tetra

Serpae tetra

Small red freshwater fish from South America

The serpae tetra is a small, reddish freshwater fish native to South American river basins. First described in 1882, it is now classified in the genus Megalamphodus. It is widely kept in home aquariums due to its bright colour, though captive breeding has reduced wild collection.

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  • Reaches a maximum length of 4 cm
  • Native to Amazon and La Plata basins
  • Known for aggression in community tanks
  • Most aquarium specimens are captive bred
  • Features a distinct black humeral spot

What it is

This small ray-finned fish belongs to the American tetra family. Adults reach a maximum standard length of four centimetres. The body is high and compressed from side to side. Its base colour is reddish-olive, turning bright scarlet on the flanks. A black comma-shaped spot sits behind the gills. The dorsal fin is black, while the tail and anal fins are red.

Where it lives

Native populations exist in two separate areas. One group lives in the Amazon basin of Brazil. The other inhabits the La Plata basin across Argentina, Bolivia, Paraguay, Uruguay and parts of Brazil. Humans have introduced the species to French Guiana and eastern Brazil. It prefers slow-moving water, such as tributaries and floodplain lakes.

How it lives

The fish thrives near submerged plants and readily enters human-made waters like reservoirs and ponds. In community tanks, it is known for aggressive behaviour towards its own kind and other tankmates. This temperament contrasts with its popularity in the pet trade. Most individuals sold today are bred in captivity rather than caught in the wild.

Fish and people

Aquarists value this species for its vivid red colouration. It is one of the most common fishes in the hobby. Large pet store chains sell it widely. Because nearly all traded specimens are captive-bred, pressure on wild populations from the aquarium trade is low. Its scientific name references a horseman, possibly due to a saddle-like mark.

Questions people ask about Serpae tetra

How large does the serpae tetra grow?

This species remains small, with a maximum standard length of four centimetres. Its body is laterally compressed and relatively high, making it appear slightly larger than its actual measurement suggests.

Is the serpae tetra suitable for community tanks?

While popular, this fish is notoriously aggressive towards both its own species and other tankmates. Aquarists should be cautious when keeping it in mixed community setups due to this behavioural trait.

Where is the serpae tetra found in the wild?

It has a disjunct range in South America, living in the Amazon basin of Brazil and the La Plata basin across several countries. It also inhabits slow-flowing tributaries and floodplain lakes.

Good reading and sources

Where this page comes from

The facts on this page come from the Wikipedia article "Serpae tetra", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.

It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.

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Photo credits on this page

The small pictures above come from Wikimedia Commons under free licences. Some are cropped to fit.

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