Fish

Neon Tetra

Paracheirodon innesi · also called neon tetra

Least Concern → omnivorecarnivore Rivers & wetlands Rainforest

A neon tetra is a fish the size of a fingernail with a stripe down its side that looks lit from within. That glow is not paint but a trick of physics, stacks of reflective cells the fish can tilt to change the colour or switch it off at night. It comes from the tea-dark streams of the upper Amazon, it needs a school of a dozen or more to feel safe, and it is one of the most kept aquarium fish on Earth.

Overview

The neon tetra, Paracheirodon innesi, is a tiny (~3.5 cm) fish of the shaded, acidic blackwater streams and flooded forest of the upper Amazon in Peru, Colombia, and Brazil. It is a micro-predator and scavenger of tiny crustaceans, insect larvae, and plant fragments. Almost all neon tetras sold today are farm-bred by the million.

The stripe

The blue-green band is a structural colour — reflective platelets in special cells, not pigment — and the fish can tilt them to change or dim it, going pale at night, when resting, or when stressed or ill. In the dim blackwater the bright stripe probably helps a school stay together.

A fish that needs a crowd

The neon tetra is an obligate shoaler. Alone or in pairs it is drab, timid, and short-lived; in a group of 10 or more it colours up and swims in the open. Neon tetra disease, an untreatable microsporidian infection, causes patchy colour loss, a bent spine, and wasting, and infected fish are removed to protect the rest.

Status

Least Concern — common in the wild and produced in vast numbers by aquaculture. Wild populations can be hit by deforestation and mining that change the blackwater streams, though the ornamental fishery also gives local communities a reason to keep the forest intact.

Neon Tetra: common questions

What is the difference between a neon tetra and a cardinal tetra?

They look almost identical at a glance, both being small, slender, silvery fish with a brilliant blue-green horizontal stripe and red toward the tail, and they are close relatives in the same genus. The reliable difference is the red. On a neon tetra the red band runs only along the back half of the body, from about the middle to the tail. On a cardinal tetra the red runs the entire length of the body, from the gills to the tail, so the lower half of the fish is red from end to end. The cardinal tetra is also slightly larger and comes mainly from the Rio Negro and Orinoco, while the neon tetra is from the upper Amazon. Cardinals are a little more demanding but are considered more robust to the neon tetra disease.

How many neon tetras should I keep together?

A minimum of six, and ideally 10 to 15 or more. Neon tetras are shoaling fish that in the wild live in groups of hundreds, and their behaviour and health depend on being in a school. Kept alone or in twos or threes, they are timid, hide, lose their colour, and can become fin-nippy and short-lived. In a proper group they school loosely in the middle and upper water, display bright colour, and are calm and active. A larger group also lets the natural social behaviour play out and dilutes any bullying. A school of neons needs a tank of at least around 40 to 60 litres, well planted with some open swimming space, and stable, soft, slightly acidic, warm water.

Why does my neon tetra look pale or lose its stripe?

A dull or faded stripe is usually normal or a sign of mild stress rather than disease. Because the colour is structural, produced by adjustable reflective cells, a neon tetra naturally turns its stripe pale and greyish at night while it sleeps, and it will also dim down when frightened, when newly moved to a tank, when the water is too hard, too cold, or poor quality, or when it is kept in too small a group. If the fish is otherwise eating, swimming normally, and schooling, improving the conditions usually restores the colour within days. Persistent colour loss combined with a curved spine, a swollen or lumpy body, erratic swimming, and wasting points to neon tetra disease, which is not treatable and calls for removing the affected fish.

Are neon tetras good for beginners?

They are a classic beginner fish and among the most popular aquarium species in the world, being small, peaceful, colourful, inexpensive, and widely available, and they suit a community tank with other small, gentle species. The one common mistake is adding them to a brand-new, uncycled aquarium, where they often die, because although an established neon tetra is fairly hardy, freshly imported or farm-raised stock is sensitive to unstable water and to the shock of being moved. The advice is to set up and cycle the tank first, keep the water soft, warm, and stable, buy a group of at least six, and add them once the tank is mature.

Sources & further reading

Written by HideShark Editorial Team · reviewed by HideShark Science Desk. Published September 11, 2026. Last updated September 11, 2026.

Quick facts

Scientific name: Paracheirodon innesi
Diet: A micro-predator and scavenger in the wild, eating tiny crustaceans, insect larvae, rotifers, algae, and fallen plant fragments from the leaf litter and water column, and in aquaria taking small flake, crushed pellet, micro-pellet, and small live and frozen foods such as daphnia and baby brine shrimp
The stripe is a trick of light: The bright blue-green band along a neon tetra's side is not a pigment but a structural colour, produced by stacks of tiny reflective platelets in special cells that bounce back blue-green light, and the fish can tilt these platelets to change the colour or dim it, turning the stripe pale at night, when resting, or when ill or stressed
A blackwater fish: In the wild the neon tetra lives in the shaded, acidic, tea-coloured blackwater streams and flooded forest of the upper Amazon in Peru, Colombia, and Brazil, where the water is soft, warm, and stained by tannins, and the bright stripe is thought to help the fish keep a school together in the dim light
It must live in a group: The neon tetra is an obligate shoaling fish, and a single one or a pair kept alone becomes stressed, drab, and nippy, hiding and often not lasting long, whereas a school of 10 or more spreads out, colours up, and swims confidently in the open, so a proper group is a welfare requirement rather than a preference
Almost all are farm-bred: The species has been bred commercially since the mid-20th century, and the neon tetras in shops today are produced by the million on fish farms in Southeast Asia, eastern Europe, and Florida, with wild collection now a small part of the trade, though wild-caught fish are still exported and are generally hardier
Neon tetra disease: A microsporidian parasite causes a well-known and essentially untreatable condition in which the fish loses colour in patches, develops a lumpy or bent spine, swims erratically, and wastes away, and because it spreads when other fish eat an infected body, affected individuals are removed promptly to protect the rest of the tank
Named after an aquarium publisher: The neon tetra was described in 1936 and named innesi after William T. Innes, an American aquarist and publisher whose books and magazine helped popularise the hobby, and it quickly became one of the defining fish of the home aquarium
Range: The upper Amazon basin of western Brazil, southeastern Colombia, and eastern Peru, in small, slow, shaded blackwater and clearwater streams, forest creeks, and flooded forest with soft, acidic, warm water, leaf litter, and submerged wood and roots, plus scattered feral populations elsewhere from aquarium releases, which rarely persist because the fish needs warm water.
Conservation status: Least Concern → ≈ The neon tetra is assessed as Least Concern, being common across its natural range in the upper Amazon and, more importantly, produced in enormous numbers by aquaculture, so the species is in no danger of extinction. Wild populations can be affected locally by deforestation, mining, and pollution that alter the chemistry and shading of the blackwater streams it depends on, and by the ornamental fishery, but the collection of neon tetras and other small characins is also an incentive for local communities to keep the forest and rivers intact, and is managed in parts of the range in the wild