Dario Dario (Scarlet Badis)

Dario dario, the Scarlet Badis or Ruby Badis, is one of the most spectacularly coloured nano fish in the aquarium hobby — and one of the smallest true predatory fish kept in aquariums. Native to the Brahmaputra River drainage in Assam, India, and neighbouring Bangladesh, where it inhabits shallow, densely vegetated, slow-moving streams and ditches.

Males are extraordinary in colour for such a tiny fish (2 cm): the body displays alternating bands of deep red to orange-red and vivid iridescent blue, creating a gem-like pattern. The dorsal fin and other fins are vivid blue-red. Females are considerably plainer — a drab brownish-silver — making sexing straightforward but also meaning that female-only groups lack the visual impact of males.

Dario dario is carnivorous and possesses a small, laterally compressed body typical of ambush predators. In the wild, it feeds on micro-crustaceans, small insect larvae, and zooplankton. In captivity, it can be challenging to feed — many specimens refuse dry foods entirely, requiring live baby brine shrimp, micro worms, Daphnia, or frozen equivalents. This feeding requirement restricts it to aquarists prepared to regularly provide appropriate live or frozen micro foods.

Males are strongly territorial toward other males — they require sufficient space and visual barriers to minimise conflict. A single male with two or three females in a well-planted nano tank, or multiple males in a large, heavily planted aquarium with clear visual territory separation, works well.

Tank Setup: A 20–40 litre nano planted aquarium for a small group. Extremely dense planting with fine-leaved plants (Java moss, Anubias nana petite, mini Pellia), cave-forming driftwood, and visual barriers. Very gentle sponge filtration — no strong current. Dark substrate enhances male colouration.

Water Parameters: Temperature 15–24°C; pH 6.5–7.5; GH 5–15 °dH; KH 2–8 °dH. Prefers cooler water than most tropical nano fish (15–22°C is ideal). Can be kept without a heater in many European homes. Avoids warm tropical conditions.

Feeding: Carnivore — live and frozen micro foods primarily. Baby brine shrimp (live or frozen), micro worms, Daphnia, Cyclops, and small bloodworm. Many individuals refuse dry foods entirely. Feed twice daily. Target-feed individual males if needed.

Tank Mates: Keep only with peaceful nano species that do not compete for the substrate: Celestial Pearl Danios (as upper-water fish), small Boraras, Pygmy Corydoras (if water temperature compatible), and adult dwarf shrimp. Any fish that can eat them or outcompete them for food should be excluded.

Behaviour: Males establish small territories and display intensely toward rival males. Females move through the tank more freely. Spawning among fine-leaved plants — eggs and fry require no parental care but are tiny and need micro foods.

Health: Hardy when kept cool with appropriate live foods. Main health risks are starvation from unsuitable diet and overheating. Provide live foods and cool water for optimal health.