Zebra danio (lat. Danio rerio) is a good looking and unpretentious fish, which is a perfect choice for a beginning aquarists. This schooling fish easily breeds in captivity and it was even used for science experiments.
Habitat in the wild
The Danio rerio dwells in rivers and streams in Pakistan, India, Bangladesh, Nepal, Myanmar and Bhutan. Inhabits in rivers, channels, ponds, rivers. The place where the fish dwells to a large extent depends on the season.
The adult species in large number can be encountered in puddles appeared during dry season and in flooded rice fields, where the fish feeds and spawns.
After the rain season the fish gets back into rivers and large water basins. In the wild feeds on insects, seeds and zooplankton.
Here things are quite complicated, since there is a variety of the coloring and fins length. However, all of them come from one and the same kind, have similar behavior and require the same care.
Classical danio is a fish with fusiform silvery body about 4 cm (1.6 in) long with bright blue stripes. Young species have short fins, in time they grow longer and form a veil (there are also long-finned species). Fins edges may be yellow. There is a pair of downward tiny barbels in the corners of the mouth.
Here I’d like to say more about a special and unique species.
Danio rerio is the first pet that was genetically modified with dioluminescence genes in 2003. Though initially the fish was bred not as a decorative one, it became the first generally available genetically modified pet.
GloFish — is a patented commercial brand name that is used to sell genetically modified fluorescent fishes; the first one here was danio rerio.
The main distinctive feature of glofish species that were artificially bred by means of genetic modification from their initial form is its red, green or orange fluorescent coloring, that becomes more visible and intense at UV light.
Transgenic fidh differ from their initial species by the body coloring. The DNA has DNA paragraphs of a jellyfish (Aequorea Victoria) and a red coral (from Discosoma kind).
Danio with a jellyfish DNA paragraph (GFP gene) have green coloring, with the coral DNA paragraph (RFP gene) — it is red; fishes that have both DNA paragraphs in their genotype are yellow colored.
In addition to red fluorescent danio rerio that is sold under the trademark Starfire Red, green and orange-yellow fidh were bred in the middle of 2006; in 2011 blue and violet colored species followed them.
These genetic lines got trademark names Electric Green, Sunburst Orange, Cosmic Blue and Galactic Purple. All these fishes were bred using genetic engineering by means of recombinant DNA taken from various sea corals.
Unlike artificially colored fishes glofish preserves its coloring through its whole life and passes it to its offspring. Due to the presence of these foreign proteins the fish brightly glows in UV light.
Transgenic form prefers warmer water — about 28°C. There wasn’t observed any differences in keeping, feeding and breeding of genetically modified fish: the transgenic fish is the same peaceful and undemanding in terms of care.
Difficulties in keeping
This is a perfect fish for beginning aquarists and an excellent choice for a community tank. Fish eats any food that you give it. They easily stands various tank water parameters and it can live even without water heating-up.
Care and keeping in a tank
|Scientific Name||Danio rerio|
|Common Name||Zebrafish, zebra danio|
|Tank size||10 gallons and more|
|Temperature||21-25 °C (70-77°F)|
|Size||up to 4 cm (1.6 in)|
This fish is amazingly not demanding, capable of living in various tank conditions. However, they have some preferences you should take it into account.
The fish dwells mainly in upper water layers. Due to this fact you won’t have to install additional aeration on the tank. A long tank is preferable for this fish, since it is very active and likes chasing its tankmates.
If fish feels endangered, it can jump out of the water right into the air. Therefore, to prevent your pet’s death the tank should be always covered with a lid.
Optimal distance from the water surface to the tank lid is about 3-4 cm to make sure that if the fish jumps out, it won’t get hurt because of hitting the firm surface of the lid.
Technically you may call the fish a cold water dweller (it lives in the water about 18-20 °C (64-68°F). However, it has adapted to a wide variety of tank parameters, because the fish is successfully bred in large numbers.
But still it’s better to maintain the tank water temperature around 21-25 °C (70-77°F), it this case is more disease-resistant.
Danio rerio live in groups. It’s better to keep them in a school of 5 species and more. This way the fish is more active and less prone to stress. For such a school a tank of 40 liter (10 US gallons) capacity. Though, the more the better – since the fish needs space to swim.
For zebra danio to feel good it is desirable to renew up to 15% of total water amount with fresh water every week and control the water hardness and acidity. Optimal water hardness is 15 dH and violent reaction of the medium about 6-7,5pH. The fish becomes reproductive at the age of 6 month.
Rerio prefers eating food from the water surface. However, if the food starts drowning the fish can catch it under the water, but it almost doesn’t eat the food from the tank bottom.
The fish is not demanding it eats all types of live, frozen or artificial food.
Compatibility and tank mates
This is a perfect fish for a community tank. It gets on well both with related species and most of other tank mates. You can keep it with any small and peaceful tank mates (not large ones like oscar fish or blood parrot).
It is better to keep at least 5 species in a tank. Such a school will have its own hierarchy and it is less prone to stress.
Zebra danio chase each other, but such a behavior doesn’t demonstrate aggression, this is how they live in a school. They don’t hurt each other and don’t harm other fishes.
It is possible to tell between the male and female only for adult species. Young species are not formed completely, so both males and females are very much alike.
If the sex is important for you, you must buy only the adult species.
The most reliable criterion to define the sex is its size. Look at the school and try to compare them.
The females are larger as a rule and they have more rounded abdomen. The males are more streamlined, but a bit smaller in size.
This peculiarity of the sexual dimorphism is connected with the ability to lay eggs and hatch the juveniles which is directly hinges on the female size.
Pay attention to the fish coloring intensity. The stripes on the female bodies are paler and less visible, while the males are brightly colored and opalescent.
You will have to put the couple separately from each other, make the tank water temperature higher and feed intensively.
The rounded body of the female will show you when it is ready to spawn.
Use a small volume with a glass bottom as a spawning tank. Experienced aquarists do not recommend to put sand on the bottom, since you won’t see how the fish lays eggs in this case.
However, it is obligatory to put some small leaved plant on the bottom (java moss, for example). Take the water for the spawning tank from the community tank, but before pour it through a siphon and add some fresh, reach in oxygen water into it.
Don’t make water level high in the spawning tank – 8 cm of water level is more than enough. This way you’ll have 4 cm of water layer above the moss.
Put one female and two male into the tank in the evening and if possible put the volume near the window.
It happened, that the tank water temperature doesn’t play any significant role in this process. It was observed, that danio easily spawns both when the temperature is 25 °C and 17 °C.
During the night the fish will get used to the new tank conditions and in the morning when the plants start producing oxygen and the volume will be well lighted they will start spawning.
I’ve never seen the fish moving so abruptly in a tank, than that of zebra danio mating game. The male try as hard as they can to make the female lay the eggs.
This process lasts about 5-6 minutes without rest and the spawning itself seldom lasts longer than an hour.
How many eggs does the female lay at one time? This is a rhetorical question, since the number of eggs is directly proportional to how ready for spawning the female is and its size. I can only give you a range of possible eggs number for one spawning: it is from 50 to 400 eggs.
You may get the offspring from just a couple, though as experience showed, in this case the eggs are not fertilized enough.
That’s why most of aquarists tend to use 2 males and 1 female for spawning. If your spawning tank is big enough, you surely can put several couples there.
Once the fish finish laying eggs remove them from the tank as well as put males and females separately. In a week or two you should put them together to perform spawning one more time.
Otherwise the eggs may get too old and there will be no juveniles; sometimes it happens that the female just won’t be able to lay eggs any more at all.
Quite often I saw complaints of some aquarists on the forums that danio rerio lay awful eggs or don’t lay eggs at all.
Both can be explained by the fact, that the fish didn’t receive proper care. It is likely, that the fish that was supposed to spawn was kept in a warm water and fed intensively for a long time. This caused over ripping of the eggs and they ‘got old’ then.
The fish won’t lay the eggs if they are old. To avoid such unpleasant surprises keep the fish you want to spawn in the water which temperature is not higher than 19 °C in winter season and don’t feed them too much.
The eggs incubation time directly depends on the temperature profile in the tank. If the temperature is 28 °C juveniles will appear in a day and a half, but at 16 °C the offspring will hatch in 2 weeks.
Once the larvae hatches from the eggs it sticks to the tank plant leaves and tank walls and hangs like there.
At first you should feed it with infusorian and as the larvae growth some larger sized food can be added to its diet.
If you keep the tank water temperature about 27°C, provide good aeration and high feeding, the fish becomes reproductive at the age of three months. The lower the temperature is, the slower the develops.