Neon Blue Rasbora (Wild) - Sundadanio Axelrodi

Sundadanio axelrodi (Wild Caught) | The Neon Blue Rasbora — A Stunning Blackwater Micro Fish

Sundadanio axelrodi, commonly known as the Neon Blue Rasbora or Blue Axelrodi Rasbora, is one of the most breathtakingly beautiful and jewel-like micro fish in the freshwater aquarium hobby. Native to the ancient blackwater peat swamps, streams, and pools of Borneo, Sumatra, and the surrounding Greater Sunda Islands of Southeast Asia, this extraordinary little fish packs a remarkable amount of colour into a body barely one inch long. The upper body glows with an intense, iridescent electric blue that shimmers and shifts under aquarium lighting, transitioning to a fiery reddish-orange on the lower body — a combination that, in a large school against dark substrate and tannin-stained water, is one of the most spectacular sights in the nano aquarium hobby.

Wild-caught specimens carry the full, undiminished expression of their natural colouration — collected directly from the pristine blackwater peat swamps of Southeast Asia where this species has evolved over millions of years.

An Important Conservation Note

The natural blackwater peat swamp habitats of Sundadanio axelrodi are under serious threat from rubber and palm oil plantations, land development, and environmental degradation. These unique and irreplaceable ecosystems are disappearing at an alarming rate. Wild-caught specimens should be kept with the respect and care their origins deserve — these are fish from one of the world's most threatened and biodiverse freshwater habitats.

Acclimating Wild-Caught Specimens

Wild-caught Sundadanio axelrodi require extra care during acclimation compared to tank-bred fish. They are unaccustomed to aquarium conditions and are particularly sensitive to parameter changes during and after shipping. Drip acclimation over a minimum of 3 hours is strongly recommended, and the receiving tank should be a mature, well-established blackwater setup that as closely as possible replicates their natural habitat from day one. Allow several weeks for wild-caught fish to fully settle before judging their colour or behaviour.

Not a Fish for Beginners — But Worth the Effort

Sundadanio axelrodi has very specific water parameter requirements that closely mirror its natural blackwater habitat — soft, acidic, tannin-rich water with stable parameters. It is not a fish for newly set up tanks or aquarists still learning the basics of water chemistry. However for those prepared to meet its needs, the reward is one of the most strikingly beautiful and fascinating micro fish available at any price point.

Sundadanio axelrodi Care Guide

Care at a Glance

• Scientific name: Sundadanio axelrodi
• Also known as: Neon Blue Rasbora, Blue Axelrodi Rasbora, Neon Blue Danio
• Origin: Borneo, Sumatra, Bangka Island, and surrounding Greater Sunda Islands — wild caught from blackwater peat swamps
• Adult size: up to 1 inch (2.5 cm) — males more intensely coloured than females
• Minimum tank size: 10 gallons — a well-established, mature nano tank is ideal
• Temperature: 73–79°F (23–26°C)
• pH: 4.0–6.5 — soft, acidic blackwater conditions are essential
• Hardness: 0–5 dGH — very soft water required
• Best kept in groups of 15 or more
• Lifespan: 3–4 years with good care

Sundadanio axelrodi Tank Setup

A mature, well-established blackwater nano tank is the ideal home for this species and will produce the most stunning display of their electric blue colouration. Dark substrate, dense planting with Java Moss, Java Fern, Cryptocoryne, and floating plants to diffuse lighting, driftwood, and a generous addition of Indian almond leaves and botanicals all help replicate the tannin-stained, dimly lit peat swamp habitat they come from. The darker and more heavily planted the tank, the more confident, active, and brilliantly coloured these fish will be.

A sponge filter is strongly recommended — gentle flow, no risk to micro fish, and an additional biofilm grazing surface. Stability is absolutely critical with this species — sudden parameter changes are extremely stressful and can be fatal. This fish should never be added to an immature or cycling tank.

A Critical Warning — Water Parameter Sensitivity

Sundadanio axelrodi does not tolerate changes in water conditions well. Drip acclimation over a minimum of 3 hours is strongly recommended when introducing new fish — particularly important for wild-caught specimens unaccustomed to aquarium conditions. Regular small water changes are preferable to large infrequent ones, and all new water should be matched as closely as possible to the tank parameters before addition. Stability matters more than perfection — a consistent pH of 6.0 is far better than one that swings between 5.5 and 7.0.

Feeding Your Sundadanio axelrodi

Micropredators that feed on tiny invertebrates and zooplankton in the wild. In the aquarium they accept high quality micro flake and nano pellet foods, but thrive with regular supplements of appropriately sized live or frozen foods — baby brine shrimp, micro worms, daphnia, and cyclops are all excellent choices. Food size is critical — their mouths are tiny and standard fish food must be crushed to a fine powder before feeding.

How Many Sundadanio axelrodi Should You Keep?

A true schooling species that should be kept in groups of 15 or more for the most natural behaviour and most impressive colour display. In a large, well-conditioned group, males display constantly — intensifying their electric blue colouration and competing for female attention in a mesmerising, shimmering spectacle.

Sundadanio axelrodi Tank Mates

• Other micro nano fish such as Chili Rasboras, Ember Tetras, and Boraras species that share similar soft, acidic water requirements
• Pygmy Corydoras and other micro bottom dwellers
• Dwarf shrimp such as Caridina and Neocaridina — good companions in a well-planted setup
• Avoid any fish larger than 1.5 inches that may view them as food
• Avoid fish requiring hard or alkaline water — water chemistry compatibility is non-negotiable with this species