Ruby Tetra Breeding Guide

Breeding Axelrodia riesei: sexing, soft acidic water requirements, an egg-scattering spawn on fine-leaved plants, and rearing fry on microorganisms.

Overview

Axelrodia riesei is a tiny characid from the upper Orinoco basin of Colombia and Venezuela, reaching a maximum standard length of about 2.5 cm. It is an egg-scattering spawner regarded as an advanced breeding subject, mainly because it demands very soft, acidic water and mature, stable conditions to spawn successfully.

Sexing

Adult males are slightly smaller and more intensely coloured than females, while gravid females appear distinctly rounder-bodied. Note that the intense ruby colour fades in captivity, so colour alone is an unreliable indicator on long-kept stock.

Conditioning

This species is sensitive to fluctuating organic wastes and should never be introduced to a biologically immature aquarium, so a well-matured, stable tank is the foundation for conditioning. Maintain the fish at 20-28 degrees Celsius, pH 4.0-6.5 and very low hardness, feeding well to bring females into condition.

Breeding Setup

Breeding requires acidic water with negligible carbonate hardness and very low general hardness, so reverse osmosis water that is further acidified is typically needed. Provide fine-leaved plants such as Taxiphyllum as a spawning medium, and adding leaf litter helps establish the microorganism populations that feed the fry.

Spawning Behavior & Trigger

Once in condition adults spawn on a daily basis, scattering eggs among fine-leaved plants. A practical approach is to place a pair, or a male with several females, into a smaller spawning aquarium and remove them after a few days, leaving the eggs and any fry to develop undisturbed.

Egg & Fry Care

The microorganisms colonising leaf litter form the primary first food for the fry. As the fry grow, they can be moved onto progressively larger foods. Specific hatch times are not documented in the consulted sources, so omit precise figures and observe the spawning tank closely.

Common Challenges

The principal obstacles are achieving and holding genuinely soft, acidic water and the species' sensitivity to organic pollution. Because the consulted sources do not detail egg predation or incubation, breeders should treat the spawning tank as a low-disturbance grow-out and rely on dense plant cover for fry survival. The reported breeding range of 20-28 degrees Celsius and pH 4.0-6.5 reflects the species' blackwater origins in the upper Orinoco basin, where it favours small tributaries; reproducing that low-mineral, slightly acidic chemistry consistently is the limiting factor. Note also that the intense ruby colour fades in captivity, so selecting breeders on body shape and condition rather than colour gives a more reliable result.