Zebra Fish

The zebrafish (Danio rerio) is a small, striped freshwater fish from South Asia and a member of the carp and minnow family, Cyprinidae. In pet shops it is often sold as the zebra danio, and in science labs it is one of the most important animals for studying how bodies grow and heal.

Scientific Classification & Quick Facts

Common name	Zebrafish
Scientific name	Danio rerio
Kingdom	Animalia
Phylum	Chordata
Order	Cypriniformes
Family	Cyprinidae
Genus	Danio
Conservation status	Least Concern
Type	Small freshwater minnow
Diet	Dry food and live brine shrimp
Habitat	Streams, ponds, canals and rice fields
Native range	Himalayan region, India, Nepal, Bangladesh
Size	Up to 6.4 cm (2.5 in)
Lifespan	2 to 3 years in captivity
Colours	Blue stripes with gold or silver

Where Zebrafish Live

Wild zebrafish come from South Asia, mainly India, Bangladesh and Nepal, with populations also reported in neighboring countries. They are especially common in the Ganges and Brahmaputra river basins.

They live in shallow, slow-moving or still water: streams, ditches, ponds, canals and flooded rice fields. The water in these places is often warm and clear in the dry season and muddy during the monsoon rains.

What Zebrafish Look Like

The zebrafish gets its name from the dark blue horizontal stripes that run along each side of its body, reminding people of a zebra’s stripes. Usually there are about five stripes, and they continue onto the tail fin. The stripes on the anal fin match too.

Zebrafish have slim, torpedo-shaped bodies and upturned mouths, good for picking food from the water surface. You can tell males and females apart:

• Males are slimmer and have a gold or yellowish tint between the blue stripes.
• Females are rounder, with a bigger, whiter belly and more silvery color between the stripes.

Zebrafish are small, usually about 1.5 to 2 inches (4 to 5 cm) long, and rarely bigger than about 2.5 inches (6 cm). In an aquarium they usually live around 2 to 3 years, and well-kept fish can live longer, up to about 5 years.

Superstars of Science

Scientists all over the world use zebrafish to learn about genes, growth and diseases. There are several reasons they are so useful:

• See-through embryos. Zebrafish eggs and embryos are almost transparent, so scientists can watch the heart, brain and other organs forming under a microscope.
• Fast growth. The beginnings of all the main organs form within about 36 hours of fertilization, and the babies hatch after about two to three days.
• Lots of eggs. A female can lay hundreds of eggs at a time, every few days.
• Amazing healing. Zebrafish can regrow damaged fins and even repair parts of their heart, retina and spinal cord. Scientists hope to learn how this works.

Some of the fluorescent fish sold as GloFish are zebrafish that scientists gave an extra gene for a glowing protein from jellyfish or coral.

How Zebrafish Grow Up

Zebrafish lay their eggs in the open, and the parents give no care. A fertilized egg starts as a single cell sitting on top of a big ball of yolk. The cell divides again and again into thousands of tiny cells, which spread down over the yolk. Within a day, a head, tail and beating heart can be seen.

After hatching, the tiny larva lives off what is left of its yolk for a few days before it starts eating. The young fish grow quickly and are usually old enough to breed at about three months.

Keeping Zebrafish at Home

Zebra danios are tough, lively and easy to keep, which makes them a popular first fish. Always set up and cycle the tank before adding fish.

Tank

Zebrafish are fast swimmers that like to dash around in groups, so length matters more than height. A tank at least 24 inches (60 cm) long, holding about 20 gallons (75 liters), is a good size for a small group. Keep at least six together; alone or in pairs they become stressed. Use a tight-fitting lid, because they can jump.

Add some plants, but leave plenty of open swimming space. Danios scatter their eggs and eat them, so breeders put marbles, mesh or fine plants on the bottom to protect the eggs.

Water and Temperature

Zebrafish handle a wider range of conditions than most tropical fish. General guidelines:

• Temperature: about 64 to 79 F (18 to 26 C). Labs often keep them a little warmer, at about 82 F (28 C).
• pH: about 6.5 to 8.0.
• Hardness: soft to moderately hard water.
• Ammonia and nitrite: should always be zero. A good filter and regular partial water changes keep the water clean.

Food

Zebrafish are omnivores. In the wild they eat small insects, insect larvae, tiny crustaceans and plant matter. At home, feed good-quality flakes or small pellets, plus live or frozen treats such as brine shrimp or daphnia. Brine shrimp eggs can be bought and hatched at home for a fresh live food. Feed small amounts once or twice a day.

Good tankmates are other peaceful, active fish of similar size, such as other danios, rasboras and corydoras catfish.

Zebrafish FAQs