Brachydanio rerio

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The Brachydanio rerio, also known as the Zebra Danio, is a small Asian fish valued for its constant activity and adaptability. Its striped body immediately catches the eye, while its schooling behaviour brings life to the upper part of a community aquarium. It is a hardy species that usually accepts food readily and suits beginner aquarists, provided it receives a sufficiently large group, clean water and a tightly covered tank. Its popularity in the hobby is high; rarity level 1 corresponds to a very common species in the aquarium trade.

General species description

The Brachydanio rerio is a small schooling cyprinid that spends much of its time in the upper and middle levels of the aquarium. In nature, it lives in soft to moderately mineralized waters in South Asia, using quiet areas or sections with gentle flow. In captivity, it should be kept in a group, ideally with at least six individuals, to encourage natural interaction and reduce stress. Its temperament is generally peaceful, although its constant activity may bother very calm fish or species with long fins. An aquarium of at least 60 litres, with good swimming length, is preferable to a small tall tank. The species appreciates well-oxygenated water, efficient filtration and regular water changes. Its tolerance of a relatively broad range of conditions explains its great popularity with beginners.

Geographic origin and biotope

Countries of reference: India, Bangladesh, Nepal, Bhutan and Pakistan. The Brachydanio rerio is associated with the Ganges basin and several drainage systems of South Asia. It inhabits shallow streams, ditches, canals, seasonal pools and rice-growing areas, often in locations exposed to sunlight. These habitats may contain clear or slightly stained water, with abundant aquatic and marginal vegetation. The bottom is generally made of sand, silt, fine gravel or plant debris. Flow ranges from low to moderate depending on the season and the position within the watercourse. Natural populations therefore use a variety of habitats, but mainly shallow waters rich in vegetation.

Precise location and local name

Within its native range, the Brachydanio rerio occurs in the plains and foothills of eastern and northeastern India, Bangladesh, southern Nepal and Bhutan. Records also include Pakistan, particularly in drainages connected to the Indus. It is commonly found in small streams, irrigation canals, ditches and temporarily flooded agricultural areas. The most widely used vernacular name is Zebra Danio, or zebrafish in some English-language contexts. In French, “danio zébré” and “poisson-zèbre” are commonly understood. Local names vary according to region and language; Zebra Danio remains the most practical trade name for aquarists.

Appearance and physical characteristics

The Brachydanio rerio has an elongated, laterally compressed body marked by horizontal metallic blue and golden stripes extending from the snout to the base of the caudal fin. Its fins are generally transparent or slightly tinted, and its upturned mouth reflects its surface-feeding habits. Adults usually reach about 4 to 5 cm, with males tending to have a slimmer outline. Females are often deeper-bodied, especially when carrying eggs, while males frequently show more intense colour. Some captive varieties have longer fins. The striped pattern and rapid swimming are its most distinctive characteristics.

General diet

In nature, the Brachydanio rerio feeds on small invertebrates, zooplankton, insect larvae and other food particles available near the surface. In an aquarium, it readily accepts quality flakes, small micro-pellets and appropriately sized frozen foods. Baby brine shrimp, daphnia and cyclops can supplement the diet and encourage natural hunting behaviour. It is better to offer small portions once or twice daily that the fish can consume quickly. A varied diet supports colour, growth and overall condition. Food should be fine enough for its small mouth; overfeeding can quickly reduce water quality. Tiny prey and floating foods are especially suitable for its open-water chasing behaviour.

Essential data

• Name of river of origin: Ganges and tributaries
• Local name used: Zebra Danio; zebrafish
• Origin of the scientific name: Brachydanio is an older genus name; rerio is the specific epithet retained from the original description.
• Full-name etymology: Brachydanio combines brachy, meaning short, with Danio, a related genus name; rerio is a historical specific name.
• Common/vernacular names: Zebra Danio, zebrafish, danio zébré, poisson-zèbre
• Family: Danionidae
• Subfamily: Danioninae
• Name pronunciation: brak-ee-DAN-ee-oh - REER-ee-oh
• Discovery: Francis Buchanan-Hamilton, 1822
• Maximum adult size: About 5 cm
• Water temperature and pH: 18 to 26 °C; pH 6.5 to 8.0
• Appearance of the watercourse and surrounding vegetation: Shallow streams, ditches, canals and pools; aquatic plants, bank grasses and rice-growing areas
• Typical tankmates: Danio kyathit, Danio dangila, Devario sondhii, Rasbora espei, Pangio kuhlii, Trichogaster chuna
• Temperament and behaviour: Peaceful, highly active and schooling; mainly swims in open water and near the surface
• Water depth: Shallow, usually from a few centimetres to about 1 metre
• Sexual dimorphism: Females are fuller-bodied; males are often slimmer and more brightly coloured
• Bottom structure and flow: Sand, silt, fine gravel and plant debris; low to moderate flow

In your aquarium

The Brachydanio rerio does very well in a mature community aquarium when kept in a group and provided with a long, open swimming area. A cover is recommended because this active fish may jump when startled. Filtration that creates moderate circulation, plants that provide shelter and regular maintenance all contribute to stability. Avoid predatory tankmates or slow species with very elaborate fins. For good results, provide well-oxygenated water, a stable temperature and fine food offered in moderation. The key factors are therefore **proper shoal maintenance**, horizontal swimming space and **consistent water quality**.