The Zebra Danio

The Zebra Danio:

The Zebra Danio (or zebrafish), is one of the most popular tropical aquarium fishes in the hobby today, and is often one of the first tropical fishes new fishkeepers have in their tanks. A different colour morph called the leopard danio, although superficially different is actually the same species. Belonging to the vast cyprinidae family, (which includes the carp and the goldfish), the fish‘s scientific name is Danio rerio. Not only is this fish important to the global aquarium trade, it is also much researched by scientists as a model organism. A short generation time and transparent embryos make this fish widely used by researchers in the fields of genetics, embryology and cancer research. It is even one of a handful of species to have been flown into space!

The fish is native to Asia, being found in slow moving to standing water bodies of countries such as Pakistan, India, Bangladesh. The fish now has much more global distribution, probably as a consequence of escape from aquaria, ornamental fish farms and research facilities. As with the other species we have examined in this series, the fish in the aquarium trade would always be captive bred rather than wild caught species.

The zebrafish is a real generalist, which is one of the keys to its success, it can live happily in water between a pH of 6 – 8, a hardness range of 5 – 19′dH and a temperature between 18 – 24′C. As with all fish stability is the key, the pH, hardness and temperature can sit anywhere between the ranges above, but must not fluctuate between them, even for spawning, the exact value is not critical.

In the wild the fish would feed on insect larvae, crustaceans, worms and many other omnivorous items, indeed the danios are often used for mosquito control as part of malaria and arbovirus eradication programs.

A minimum home aquarium size of 60L is recommended as danios prefer to live in shoals of 5 or more individuals. The tank should have plenty of cover in the form of real or plastic plants. Danios will take any common tropical aquarium fish foods; base their diet on a quality flake or crisp food, but offer regular treats of bloodworm, brine shrimp, or daphnia.

In the wild, the danios spawn at the onset of the monsoon season. Breeding the fish in the home tank, involves preparation of a breeding tank – the fry would simply not survive in the display community aquarium. The 60L breeding tank should have a thin layer of marbles or similar sized gravel over the bottom, this prevents the parents from eating the eggs following spawning. Cover of feathery leaved plants such as Cabomba give the pair cover and security. Condition the fish prior to spawning by increasing the feed rates and increasing the amount of treat foods such as bloodworm. (Monitor water quality to make sure that the increased feeding rate does not cause a rise in ammonia or nitrite levels, this will stress the fish and hinder the spawning process) .

Once a pair of fish can be selected from the shoal, place them in the breeding tank. Courtship commences with the male frantically chasing the female, they then enter an S-shaped spawning embrace. The female lays around 400 eggs which are fertilised by the male. The eggs fall down into the gaps between the marbles / stones. Hatching occurs after 4 days at 24′C and the fry then accept infusoria or liquid fry foods after a further 3 days. The young grow very rapidly reaching 2.5 cm after only 8 weeks! The young become sexually mature very rapidly and spawning can occur several times throughout the year, making the danios a very prolific little fish!