Cardinal tetra

Care at a glance

Overview

Keep them in a school of six or more, and honestly a dozen or more looks far better and settles them down. They swim in the middle of the tank and a 60 liter is plenty for a group. They are peaceful and eat small foods readily: micro-pellets, crushed flake, and frozen brine shrimp or daphnia. Soft, acidic, stable water is the main thing they ask for, so let a tank mature before adding them.

In the wild

Cardinal tetras come from blackwater and clearwater streams in the Amazon, especially the Rio Negro and Orinoco systems, under heavy rainforest shade. The water there is very soft, acidic, and stained dark by tannins. To match it, use a dim tank with driftwood, leaf litter, and gentle flow, soft and acidic with a pH on the low side and temps in the mid to high 20s C.

Good to know

This is a small characin in the family Characidae, reaching about 4.5 cm. The red stripe runs the full length of the body, which separates it from the similar neon tetra. Most cardinals in the trade are still wild-caught, so they can be a little more sensitive to water quality than tank-bred fish.

Did you know

The red and blue stripe is structural color, made by stacked crystal-like cells that bend light rather than by pigment. The fish can tilt those cells to dim or brighten the blue, which is why a stressed or sleeping cardinal looks washed out and a settled one glows.

Related species

• 

  Neon tetra

  Paracheirodon innesi

  1.5 in (3.8 cm)11 gal (40 L)70–77°F (21–25°C)

• 

  Green neon tetra

  Paracheirodon simulans

  1 in (2.5 cm)15 gal (55 L)72–86°F (22–30°C)

• 

  Garnet tetra

  Hemigrammus pulcher

  1.8 in (4.5 cm)20 gal (75 L)73–82°F (23–28°C)

• 

  Head-and-taillight tetra

  Hemigrammus ocellifer

  1.8 in (4.5 cm)17 gal (65 L)75–82°F (24–28°C)

• 

  Mayan Tetra

  Hyphessobrycon compressus

  1.8 in (4.5 cm)16 gal (60 L)68–79°F (20–26°C)

• 

  Ornate tetra

  Hyphessobrycon bentosi

  1.8 in (4.5 cm)20 gal (75 L)72–82°F (22–28°C)