There are different types of danio with the most common like zebra (insert picture), leopard and pearl danio. Except for the giant danio, the rest are quite tiny which typically measures about 4 to 5 cm in length and all of them have an elongated body shape which makes them fast swimmers. Certain danios like the zebra fish has beautiful stripped blue white marking while the leopard danio has body marking with black and yellow spots. Pearl danio looks much simpler and they are generally grey and silver in color with slight shiny glow.
In terms of characteristic and behavior, they are generally peaceful and they won’t bother or care about presence of other types of fish although at times there will be some fin nipping occurrences take place but somehow this is not serious. They can be mixed with other tropical species like swordtail, neon tetra, hatchet fish, platy, guppy and corydoras catfish but I would avoid putting them with other larger sized fish such as angelfish, convict cichlids or discus because they will end up getting chased after and harassed.
When it comes to water quality, they will accept and thrive in water with pH between 6.0 to 8.0. The water temperature can be anywhere between 23 up to 27 degree Celsius although the best should be somehow close to the upper region at 27 to promote better appetite. When it comes to food, they will accept just about anything like floating flakes, pellet and mix of occasional live food will be beneficial to promote nice coloration.
Danios can sometimes be susceptible to spread of aquarium fish disease especially ich. When they are infected, the fish will most of the time stay still and will not accept any food. The body will lose coloration and occasionally you could see them dashing from one end to another trying to scratch their body on gravel bed surface. If you focus clearly, you could even see presence of white color dots appearing on their tiny fin. As such, it is important that you have good aquarium filter to maintain crystal clear water quality all the time. Periodic water testing is also important as part of tank maintenance and a good aquarium fish keeping practice is to perform regular water changes to prevent breakout of disease. See page on ich treatment for better understanding.
Breeding danio should be rather easy as there is no special attention required. The fish that form pairs will spawn and discharge their tiny eggs among aquarium plants and the parents would not care for the fry and will even eat the eggs. If you intend to breed large numbers of danio fish, then I would suggest removing all the other tank mates including the parents to another separate aquarium. However, as what I would normally do, I will just leave the fry to fend for themselves similar like in the wild natural selection and if you have aquarium full of vegetation with sufficient hiding spot, 2 to 3 danios will eventually survive and reach adulthood.