Emerald Dwarf Rasbora (Danio erythromicron)

The Emerald Dwarf Rasbora (Danio erythromicron) is a jewel of the nano aquarium world, native to the ancient Inle Lake in Myanmar's Shan State — one of Asia's most biodiverse and unique freshwater ecosystems. Despite being reclassified from the genus Microdevario into Danio, this species retains the common name 'rasbora' in the hobby due to its historical classification.

Reaching only 2–3 cm in length, D. erythromicron is distinguished by its extraordinary coloration: the body shimmers with metallic emerald-green iridescence while the flanks are crossed with 10–14 vertical orange-pink bars that glow under proper lighting. Males display more intense colors, particularly during courtship, while females are slightly larger and rounder.

Inle Lake itself is unusual — a high-altitude lake at approximately 900 meters elevation with unique water chemistry that is slightly hard and alkaline, quite different from the soft, acidic conditions associated with most Asian nano fish. This makes D. erythromicron an interesting exception among nano rasboras, tolerating and even preferring harder, cooler water.

In the aquarium, Emerald Dwarf Rasboras are peaceful schooling fish that occupy all water levels, though they tend to hover in the middle and upper zones. They are best kept in groups of 10 or more where their natural social behavior, including displays and spawning rituals, can be observed.

Unlike most nano rasboras, Emerald Dwarf Rasboras prefer slightly cooler water (18–25°C) reflecting their high-altitude Inle Lake origins. pH should be maintained between 7.0–8.0 with moderate hardness of 5–15 dGH. They are less tolerant of warm temperatures than typical tropical fish.

A minimum 40-liter densely planted aquarium is recommended for a group of 10. Fine-leaved plants such as Java moss, Rotala, and Staurogyne provide ideal cover and spawning sites. A dark substrate, driftwood, and gentle filtration create conditions that enhance their colors.

Feed micro-sized foods: nano pellets, micro worms, baby brine shrimp, daphnia, and crushed flakes. Their mouths are extremely small — food must be tiny enough to be ingested. Feed 2–3 times daily in small amounts.

Emerald Dwarf Rasboras are entirely peaceful and can be kept with other small, peaceful species of similar size: Chili Rasboras, Sparkling Gouramis, small Corydoras, and small shrimp. Avoid active or nippy species that may stress or outcompete them for food.

Maintain groups of at least 10 for natural schooling behavior and to reduce individual stress. Regular water changes of 20–25% weekly are important, using dechlorinated water matching the tank temperature to avoid cold shock. This species can be sensitive to sudden parameter changes.