Zebra Danio
Published
The zebra danio, or zebrafish, is small, tough and never still. Its blue and gold stripes and its easy-going nature have made it a first fish for generations of aquarium keepers — and it has a second career as one of the most important animals in biology.
Where zebra danios come from
Wild zebra danios live in the rivers, streams, ditches and rice paddies of South Asia, especially the Ganges and Brahmaputra basins. Many of these waters change a lot over a year, from warm and still in the dry season to cool and fast in the monsoon, which is part of why the species copes with such a wide range of conditions. In the aquarium it is happy at room temperature in most homes and rarely needs a heater.
A fish that changed science
Zebrafish embryos are transparent and develop outside the mother, from a single cell to a swimming larva in a few days, so scientists can watch organs form under a microscope. The fish breed often, grow up fast and share most of their disease-related genes with humans. Since the 1970s they have become a standard lab animal for studying development, genetics and disease. They can even regrow damaged fins, heart tissue and parts of the retina, which researchers hope to learn from.
Stripes, spots and long fins
The wild fish has horizontal blue stripes on a silvery-gold body. Breeders have kept several variations: the leopard danio, once thought to be a separate species, is a zebra danio with spots instead of stripes, caused by a change in a single gene. There are also golden and albino forms, and long-finned versions of most of them. Brightly coloured "glow" danios sold in some countries are genetically modified with genes from jellyfish and corals.
Keeping zebra danios
Zebra danios are fast swimmers and use the whole length of the tank, mostly the upper half, so a long tank is better than a tall one. Keep them in a school, where they chase each other in harmless play. They are egg scatterers and eat their own eggs, so breeders use a tank with marbles or mesh on the bottom that the eggs fall through. A tight lid matters: a startled danio can jump.