Blue danio
Blue danio

Blue danio - Danio kerri

Blue danio
Blue danio - Pictures by

Common name: blue danio
Scientific name: Danio kerri
Synonyms: Brachydanio kerri
Size: 5 cm / 2 inches
Temperature: 22 - 25 °C (73 - 77 °F )
Hardness: 7 - 12 dH
Lifespan: 6 years (usually only 2-4)

The Blue danio is hardy little aquarium fish highly suitable for beginners. It is a friendly species that won’t hurt or disturb anything that is too large to be eaten. They are a shoaling fish and should never be kept in groups of less than 6-8 specimens. An even larger shoal is better. This species is relatively common in the aquarium trade and you should be able to find it if you want it.  The Blue danio was very popular in the old days due to its hardiness and due to the fact that it accepts colder water. This species still deserves our love and attention.

The Blue danio originates from Asia where it is found on the Malay Peninsula. They live in clear streams and in pools surrounding these streams. Their typical environment contains a lot of open water and some plants such as cryptocoryne species, but they can also be found in more densely vegetated places.

The Blue danio is ideal for community aquariums and can be kept with most other small species as long as those species don’t get spooked by this active and fast moving species. Blue danios mainly stay near the surface but will go down to the bottom to find food. This is a very curios species and they will try to nibble on your arm hair or on your hands when you clean the aquarium to see if they can find something to eat. They show the same behavior in the wild. 

Aquarium & care

The Blue danio requires very little from the fish keeper and will fit right into most setups as long as you avoid the extremes. You can to a large extent model the decoration after the need of your other fish species as long as you leave open areas for the Blue danios to swim in. If you want to take the preferences of the Blue danios into consideration you can include a few densely planted areas along the sides and the back of the aquarium.

The Blue danio prefers clean well oxygenated water and good filtration is therefore important. You will often sea your danios playing in the strong current near the exhaust vent on the filter. Using an air pump to get a higher oxygen level in the water can also be a good idea if you keep a lot of fish and few plants in your tank. Blue danios like it when the morning light hits the aquarium but this can cause an algae problem unless you have creatures in the tank willing to eat algae. Moring light is not necessary for their well fare; they will thrive even without it.

Feeding Blue danio

The Blue danio is very easy to feed and will accept just about any food. They can be kept and bred on high quality flake food alone but should preferably be provided with a more nutritious and varied diet. You can for instance use flakes as a base and supplement with both meaty foods (such as frozen and live mosquito larvae) and vegetables. Well fed fish will show more vibrant colours.

Sexing Blue danio

The Blue danio can be sexed in the same way as other danios, e.g. the Zebra fish. The males are smaller and more slender. The females are larger and much fatter. It is very easy to tell and adult male from an adult female.

Breeding Blue danio

The Blue danio is very easy to breed and they often spawn in community aquariums. It is however rare for any fry to survive. The species is an egg scatterer and do not carry out any type of parental care. They will eat their own egg and fry if they come across them.

Blue danios are best breed in pairs in breeding aquariums receiving morning sunlight. The aquarium bottom should be covered with a mesh or two layers of marbles that allow the egg to fall through to protect them from the adults. The aquarium should also contain some fine leafed plants.  It is often best to add the female to the breeding tank one day before the male.  They usually span within 24 hours from the male being added. If not, it might help to lower the water temperature to trigger spawning. The fish should be conditioned with a varied diet before being used for breeding. To get the maximal amount of fry you separate females and males for a few weeks while conditioning them before using them for breeding.

Remove the parents once spawning is completed. The fry becomes free swimming after roughly seven days and should be fed infusorians or other very small food. As they grow bigger you can switch to larger food such as newly hatched brine shrimp and later crushed flake food.