Rathburn/Redbelly Tetra

About the Rathburn (Red Belly) Tetra

The Rathburn Tetra, more commonly known as the Red Belly Tetra, is a lively and attractive South American schooling fish prized for its shimmering silver body, vibrant red belly, and active swimming behaviour. Native to the Paraguay and Paraná River systems of South America, this hardy tetra is an excellent choice for aquarists looking to add movement and colour to a freshwater community aquarium.

As the fish matures, the lower half of its body develops an increasingly vivid crimson-red colour, particularly in healthy males and during breeding displays. Combined with its reflective silver scales and transparent fins, the Red Belly Tetra creates a striking display, especially when kept in large schools.

Rathburn Tetras thrive in planted aquariums with open swimming areas, driftwood, and gentle water movement. They are highly social fish and should always be kept in groups of at least 8–10, where they exhibit natural schooling behaviour and become significantly more confident. Their peaceful temperament makes them excellent companions for Corydoras, Rummy Nose Tetras, Cardinal Tetras, Harlequin Rasboras, Rainbowfish, Gouramis, and other similarly sized community fish.

A varied diet of premium tropical flakes, micro pellets, frozen bloodworms, baby brine shrimp, daphnia, cyclops, and other live or frozen foods will maximise their colouration and maintain excellent health.

Hardy, colourful, and constantly active, the Rathburn (Red Belly) Tetra is an outstanding addition to planted aquariums and peaceful freshwater community tanks.

Quick Care Guide

Scientific Name

Aphyocharax rathbuni

Common Name

Rathburn Tetra (Red Belly Tetra)

Origin

Paraguay and Paraná River Basins, South America

Adult Size

5–6 cm

Temperament

Peaceful

Diet

Omnivore

Minimum Tank Size

75 Litres

Temperature

22–28°C

pH

6.0–7.5

Water Hardness

2–15 dGH

Difficulty

Beginner

Lifespan

4–6 Years

Suitable For

Planted aquariums, community aquariums, and South American biotopes

Frequently Asked Questions

How many Rathburn Tetras should I keep?

Rathburn Tetras are schooling fish and should always be kept in groups of at least 8–10. Larger schools produce more natural behaviour and stronger colouration.

Are Rathburn Tetras peaceful?

Yes. They are peaceful, active community fish that mix well with most similarly sized non-aggressive species.

What do Rathburn Tetras eat?

They thrive on premium tropical flakes, micro pellets, frozen bloodworms, baby brine shrimp, daphnia, cyclops, mosquito larvae, and other small live or frozen foods.

Can Rathburn Tetras live with shrimp?

Adult Cherry Shrimp and Amano Shrimp are generally safe, although very small shrimplets may occasionally be eaten.

Why is my Red Belly Tetra losing its colour?

Stress, poor water quality, an inadequate diet, or keeping too few fish together can cause the red colouration to fade. Clean water, quality nutrition, and larger schools help maintain their vibrant appearance.

Common Mistakes

Keeping them in small groups

Red Belly Tetras become nervous and less colourful when kept in groups smaller than eight.

Poor water quality

Regular water changes and stable water parameters are essential for long-term health and vibrant colours.

Feeding only dry foods

A varied diet including frozen and live foods enhances colouration, immune health, and breeding condition.

Housing them with aggressive fish

Choose peaceful community species that won't harass or outcompete these active schooling fish.

Not providing enough swimming space

These energetic fish appreciate long aquariums with plenty of open water to school naturally.