Emerald Dwarf Rasbora Breeding Guide

How to breed Microdevario erythromicron: sexing, conditioning, a small spawning container, egg care after the parents are removed, and raising the fry.

Overview

Microdevario erythromicron (also placed in Celestichthys and historically Microrasbora) is an egg-scattering cyprinid endemic to Inle Lake in Myanmar, where it is listed as Endangered on the IUCN Red List. It is an egg-scattering spawner that shows no parental care, and conditioned adults spawn readily, making it an attainable subject for an intermediate aquarist who can dedicate a small breeding container.

Sexing

Females grow slightly larger and develop a noticeably rounder belly, especially when gravid. Males show well-defined iridescent blue vertical bars on the flanks and more red colouration in the fins. These differences become clearest on well-fed, mature fish.

Conditioning

Condition adult groups together on a varied diet so that males colour up and females fill with eggs. The species prefers cooler, harder water than most tropical fish, reflecting its high-altitude lake origin. Maintenance parameters are a temperature of 20-24 degrees Celsius, pH 7.0-8.0 and hardness of roughly 215-357 ppm; it does not thrive in acidic water.

Breeding Setup

Transfer selected pairs or small groups to a separate 10-15 litre container filled with aged water. Densely plant it with fine wool mops or Taxiphyllum so that scattered eggs fall out of reach. Neither lighting nor filtration is strictly necessary, though a small air-powered sponge filter may be used.

Spawning Behavior & Trigger

Adults in good condition spawn regularly, depositing around 30 mildly adhesive eggs in a typical event among the plants or mops. Because the parents will eat any eggs they find, they must be removed immediately after spawning.

Egg & Fry Care

Incubation takes around 72 hours, and the fry become free-swimming about 3-4 days later. Begin feeding with Paramecium or a proprietary dry food of 5-50 micron grade, then introduce Artemia nauplii and microworms once the fry are large enough to accept them.

Common Challenges

The main losses come from egg predation, so prompt removal of adults is essential. The small clutch size means yields per spawn are modest, and the fry's tiny initial gape demands genuinely small first foods such as infusoria-grade cultures before Artemia. Because the species naturally favours cooler, harder, near-neutral to alkaline water, attempts to spawn it in the warm, soft, acidic conditions used for many tropical egg-scatterers tend to fail; matching the Inle Lake profile of 20-24 degrees Celsius and pH 7.0-8.0 is more important than any single trigger. Its Endangered IUCN status also makes captive propagation worthwhile, so prioritising stable, well-conditioned breeding stock benefits the species as well as the aquarist.