Description
The zebra danio has been the classic beginner recommendation for decades, and for good reason: it is probably the hardiest freshwater fish you can buy. Five centimetres, horizontal blue stripes over a golden background and energy that never runs out.
What almost nobody tells you is that it is not a tropical fish. It comes from streams in northern India with strong seasonal swings, and thrives between 18 and 24 degrees. That makes it one of very few species you can keep without a heater in a normal home.
And here is the commonest mistake with this species, which is also counter-intuitive: putting it in a tropical community at 26 or 27 degrees. It does not die at once — which is why nobody makes the connection — but it speeds up its metabolism and halves its lifespan. A danio that should live five years stops at two.
One detail gives it another dimension: this is the laboratory zebrafish. Its embryos are transparent and develop outside the mother, which made it possible to watch a vertebrate form in real time. It is used in thousands of laboratories worldwide and its genome is fully sequenced. The fish in your tank is one of the most important model organisms in biology.
Behavior
Peaceful, but tireless. It never stops and swims at full speed along the upper band. That energy is part of its charm and also its main compatibility problem.
It forms a loose shoal: it does not swim tightly packed, but it needs a group of six or more. In small groups a behaviour appears that surprises anyone who bought it as a calm fish: it starts nipping long fins. It is not malice, it is boredom and lack of social structure.
It lives well with other cyprinids, corydoras, otocinclus and bristlenose. It fits especially well in unheated cool-water tanks, where the options are limited.
Avoid housing it with bettas and gouramis, which its constant activity exhausts and whose fins it may nip; slow or shy fish, which go without food; and tropical species needing 26 degrees or more, because one of the two will always live outside its range.
With shrimp: adults are safe. Fry are not.
And as with the rummy-nose: it needs length more than litres. It is a long-distance swimmer and a short tank frustrates it.
Habitat
Danio rerio lives in streams, channels and rice paddies of northern India, Bangladesh and Nepal. The water is shallow, clear and moderately flowing over gravel beds, and — this is the important part — subject to strongly marked seasonal temperature swings: in winter it drops well below twenty degrees.
That is the biological reason behind everything else. It is not that the danio tolerates cold: it needs it. A cooler winter is part of its natural cycle and probably contributes to its longevity.
In the aquarium that translates into something convenient: you can do without a heater if your home does not drop below 18 degrees. And if you have a tank in a cool room and do not know what to put in it, the danio is one of the best answers.
It appreciates flow. A filter that moves the water well, with some surface agitation, reproduces its stream better than a still tank.
El pez Danio rerio es una especie de cardumen, lo que significa que, de forma natural, vive y se desplaza en grupos numerosos y coordinados.
Se recomienda mantener un mínimo de 6 individuos para que se sientan cómodos y reducir su nivel de estrés.
Details
🌊 Water parameters
🐠 Minimum tank size
Breeding
It is probably the easiest fish to breed there is, and for that very reason it is the one people learn on.
It spawns at dawn, scattering eggs across the bottom without tending them at all — in fact it eats them. The classic trick is to cover the bottom of a small tank with marbles or a mesh: the eggs fall into the gaps and out of the parents' reach. Raise the temperature a couple of degrees, feed well on frozen food for a few days beforehand and they spawn almost without fail.
The fry hatch in two or three days and grow fast. They move from infusoria to brine shrimp nauplii within a week, which makes raising them far less frustrating than with a tetra.
If you have never bred fish, this is the one to start with.
Diet
Omnivorous and thoroughly voracious. It eats anything that fits in its mouth and always gets there first.
- Staple: quality flake or micropellets.
- Supplement: frozen daphnia, brine shrimp and mosquito larvae, twice a week.
- Fry: infusoria for the first days, then brine shrimp nauplii very soon after.
The problem is not feeding it, it is feeding everyone else. A shoal of danios sweeps the surface in seconds, and in a community with corydoras, otocinclus or any unhurried fish, the others systematically go without.
The fix is simple: spread the food across several points at once, or feed the danios at one end of the tank while dropping sinking wafers at the other.
Plan your next aquarium
Is this fish right for you? Plan a suitable aquarium before setting it up.