Two-spot Astyanax (Astyanax bimaculatus) Breeding Guide
Breeding Astyanax bimaculatus: a large, hardy egg-scatterer with weakly adhesive eggs laid in low-current water, with a January-February spawning peak.
Overview
Astyanax bimaculatus is a large, hardy and widely distributed characin found from Panama to the Amazon basin, reaching up to about 17.5 cm. It is named for its two dark marks: a strong humeral (shoulder) spot and a blotch at the base of the caudal fin. It is an egg-scattering species; gametogenesis takes place in the dry season so reproduction can begin with the rains, and spawning has been achieved in captivity.
Sexing
Sexes are best told apart by body condition in mature fish, with egg-laden females appearing rounder. Detailed external dimorphism is not described in the consulted sources.
Conditioning
Given the adult size, use a large, well-filtered tank and condition the fish on a varied diet. Because the species is capable of year-round reproduction with a peak in January and February, and is least active in May to July, conditioning is most effective approaching the natural spawning peak.
Breeding Setup
- A large spawning tank suited to a tetra of up to about 17.5 cm.
- Soft to moderately hard water within the species range (pH 5.5-7.5, up to about 25 dH, roughly 20-28 C).
- Areas of low water current, since the eggs are laid in calm water.
- Fine-leaved plants or a protective base to receive the scattered eggs.
Spawning Behavior & Trigger
The eggs of A. bimaculatus are weakly adhesive and are laid in environments of low current. The species can reproduce year-round, with the spawning peak in January and February, and it is less likely to be in active reproductive condition during May, June and July. Mimicking the onset of the rainy season helps trigger spawning.
Common Challenges
As an egg-scatterer the adults may consume the eggs, so a protective spawning medium or removal of the adults is advisable. The large adult size demands ample tank space, and detailed fecundity figures are not given in the consulted sources.