Exclamation Point Rasbora (Boraras urophthalmoides) Breeding Guide

How to breed the Exclamation Point Rasbora (Boraras urophthalmoides): a continuous egg-scatterer that spawns into moss with no parental care, in soft, acidic water.

Overview

Boraras urophthalmoides is an egg-scattering, continuous spawner that exhibits no parental care. In a well-established, densely planted aquarium small numbers of fry may appear naturally without intervention; for higher yields a dedicated spawning setup is used.

Sexing

Mature females are noticeably rounder-bodied and often a little larger than the slightly more colourful males. This difference is the most practical way to select spawning groups.

Conditioning

Condition adults well, then introduce two to three pairs to the spawning container; if conditions suit them, spawning typically begins the following morning. Although this species will eat its eggs, it does not appear to actively hunt for them.

Breeding Setup

Use a small 10-15 litre container with dim lighting and either a bare base or a mesh that lets eggs fall through but keeps adults away from them. Fill roughly half the space with java moss or other fine-leaved plants, and add a small air-powered sponge filter. Spawning water is soft and acidic: pH 5.0-6.5, hardness 1-5 °H, with temperature toward the upper end of the normal range (around 28 °C).

Spawning Behavior & Trigger

As a continuous spawner the species scatters small batches of eggs among the moss and fine plants. The adults should be left in place for no more than a couple of days, then removed before they eat significant numbers of eggs.

Egg & Fry Care

Eggs hatch within about two days, and the fry then subsist on their yolk sacs for roughly 24 hours. Their first food must be very small, such as Paramecium or other microscopic organisms; after 7-10 days they can take Artemia (brine shrimp) nauplii and microworms. Delay water changes for the first one to two weeks to avoid shocking the tiny fry.

Common Challenges

The main hurdles are providing first foods small enough for the extremely tiny fry and avoiding losses from premature water changes. A mesh or bare base, plus prompt removal of adults, limits egg predation.