Small Eyes Red Rasbora - Microdevario microphthalma Fish Profile & Care Guide
Introduction
The Small Eyes Red Rasbora (Microdevario microphthalma) is a tiny danionid native to southwest Yunnan in China. It was first described as Microrasbora microphthalma, but is now recognised as a valid species in the genus Microdevario. Adults remain very small, making it one of the more genuinely “nano” cyprinids in the hobby. In the aquarium, treat Small Eyes Red Rasboras as a social shoaler. Keeping a proper group makes a noticeable difference to confidence, feeding response, and how naturally the fish use open water. As a practical benchmark, aim for 10 or more individuals if space allows, rather than trying to “pair” or keep a handful. This matches established husbandry guidance for closely related Microdevario species, which show their best behaviour and colour in larger groups.
Given its very small size and tendency to be outcompeted at feeding time, Small Eyes Red Rasboras does best with peaceful tankmates that stay small and remain calm during meals. Other gentle nano cyprinids and similarly quiet micro fish are ideal, with small, non-aggressive bottom dwellers as suitable companions if you want extra activity on the substrate. Larger community fish, fast boisterous swimmers, and anything even mildly predatory are best avoided, as stress and competition are usually the real problem rather than outright aggression. For the most reliable results, a species tank or a carefully planned nano-only community is often the safest approach.
For Small Eyes Red Rasboras, aquarium success comes from recreating a clean, well-oxygenated stream-style setup rather than a warm, stagnant community tank. Provide steady filtration and consistent circulation, with open swimming space broken up by smooth stones, wood, and patches of planting to give the shoal a sense of security. A fine sand or smooth gravel base suits their natural behaviour, while subdued lighting and darker areas of cover help them settle and colour up. Keep the system stable and well-maintained, as these tiny fish are far more affected by poor water quality and heavy organic build-up than hardier, larger community species.
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Sexual Dimorphism
Sexual dimorphism in Small Eyes Red Rasboras is subtle and often difficult to confirm with certainty. In the aquarium, sexing is usually based on a combination of minor cues rather than any single definitive feature. Mature females may appear slightly deeper-bodied, particularly when gravid, while males are often slimmer and can show marginally longer unpaired fins when in prime condition. Even so, there is significant overlap among individuals, so the most reliable approach is to keep a small group and observe behaviour and body shape changes during conditioning and spawning.
Quick Facts
| Scientific Name | Microdevario microphthalma |
|---|---|
| Year Described | 2008 |
| Kingdom | Animalia |
| Classification | Actinopterygii |
| Order | Cypriniformes |
| Family | Danionidae |
| Genus | Microdevario |
| Origins | China |
| Approx Max Size | 3 cm |
| Temperament | Peaceful |
| Aquarium Level | Bottom - Middle |
| Difficulty | Beginner - Intermediate |
| Shoaling | Yes |
| Best kept as | Groups 8+ |
| Diet & Feeding | Omnivore |
| Reproduction | Egg-Scatterer |
| Average Lifespan | Up to 2 Years |
Water Parameters
| Water Type | Freshwater |
|---|---|
| pH | 6.5 - 7.0 |
| GH | 3 - 8 |
| KH | 0 - 3 |
| TDS | 50 - 150 |
| ℉ | 68 - 79 |
|---|---|
| ℃ | 20 - 26 |
Natural Habitat
The Small Eyes Red Rasbora is currently known only from the Nanwan River in southwest Yunnan, China. The Nanwan River is a tributary of the Ruili River within the upper Irrawaddy drainage, and no wider natural range is confirmed in that source. In the wild, it has been collected from a small hill stream with clear water, a sandy substrate, and numerous cobblestones, indicating a habitat shaped by steady flow and good oxygenation rather than stagnant margins. The type series was collected from a specific microhabitat near the bank, suggesting it may favour marginal zones where the current is moderated, but water quality remains stream-like.
Breeding
Breeding in Small Eyes Red Rasboras follows the typical pattern seen in Microdevario and other tiny danionids. They are egg scatterers that release small eggs among fine-leaved plants and décor, and they do not provide parental care. In well-established, densely planted aquaria, small, low-level spawnings can sometimes happen without special intervention, but the adults will readily pick off eggs and tiny fry if they find them.
If you want to raise fry in useful numbers, the usual approach is to condition a group well, then give them a dedicated spawning setup with spawning mops or dense moss and a way for eggs to fall out of reach. Once spawning occurs, remove the adults to prevent egg predation, then raise the fry on suitably tiny first foods until they are large enough for powdered and small live foods.
Diet & Feeding
In the wild, Small Eyes Red Rasboras feed on very small suspended foods. In the aquarium, offer foods that match its small mouth and feeding style. A staple of finely crushed quality flake or small granules works well, backed up with appropriately sized live or frozen options such as daphnia and other small meaty foods to support condition and natural foraging. Keep portions modest and avoid leaving excess food to break down, as nano fish are easily affected by deteriorating water quality.
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Published: 19 Feb 2026
Last Updated: 19 Feb 2026