Zebra Danio

Overview

The Zebra Danio (Danio rerio) is a small, hardy, endlessly active schooling fish marked with horizontal blue-and-gold stripes. It is one of the easiest aquarium fish to keep and breed, tolerant of a wide range of conditions, and is also one of the most important laboratory animals in science, where it is known as the zebrafish.

Natural History

Native to the streams, rice paddies, and seasonal pools of South Asia, particularly India, Bangladesh, and Nepal. It lives in clear to slightly turbid moving water, often in large shoals. Its adaptability to temperature and water chemistry reflects these variable seasonal habitats.

Appearance

Adults reach 4-5 cm. The body is slim and torpedo-shaped with five horizontal blue stripes running from gill to tail over a silver-gold background. Long-finned and genetically modified fluorescent (GloFish) varieties are also widely sold.

Temperament & Tankmates

Peaceful, fast, and constantly swimming. Zebra danios are obligate shoalers and must be kept in groups of at least 6, ideally 8-10 or more; small groups become nippy and stressed. Their speed and energy can intimidate slow or long-finned fish.

Excellent in active community tanks with other robust, fast species such as other danios, rasboras, larger tetras, and corydoras. Avoid pairing with very slow or delicate long-finned fish, whose fins may be nipped.

Tank Size & Setup

Minimum: 75 L (20 gallon) for a shoal, favouring length over height for swimming room.

They appreciate a gentle to moderate current that mimics flowing streams. Provide open swimming space along with some planting and cover at the sides. A secure lid is important, as danios are accomplished jumpers.

Water Parameters

• Temperature: 18-25°C - tolerant of cooler water than most tropicals.
• pH: 6.5-8.0.
• Soft to hard water.
• Ammonia 0, nitrite 0, nitrate <40 ppm.

Diet

Omnivore. They readily accept quality flake and micro-pellet staples, supplemented with frozen or live daphnia, bloodworms, and brine shrimp. As surface and mid-water feeders they take food quickly. Feed small amounts once or twice daily.

Health & Lifespan

3-5 years.

Common concerns:

• Ich (white spot) - often appears after temperature swings.
• Fin rot from poor water quality.
• Stress and nipping from being kept in too-small groups.
• Mycobacteriosis (fish TB) - occasionally seen in older or stressed danios.

Pros & Cons

Pros: extremely hardy, tolerant of cool water, peaceful, active, easy to breed, good beginner shoaler. Cons: constant fast movement can stress calmer fish; can nip long fins; relatively short lifespan.