Breeding Bronze Corydoras

How to breed Corydoras aeneus: sexing, the cool-water change spawning trigger, the T-position embrace, egg deposition on glass and raising the fry.

Overview

The Bronze Corydoras (Corydoras aeneus) is an egg-scattering callichthyid catfish of intermediate breeding difficulty. It is one of the more readily bred Corydoras, spawning on the aquarium glass and plants after a cool-water trigger.

Sexing

Females are larger and noticeably rounder and broader-bodied than males, especially when gravid. A breeding group works best at a ratio of about two males per female.

Conditioning the Breeders

Condition the group well so that females fill with eggs. When they look ready, the spawning trigger is a large 50-70% water change with cooler water, plus increased oxygenation and flow, repeated daily until the fish spawn.

Spawning Behavior

Eggs are normally deposited on the aquarium glass, though it is recommended to also provide fine-leaved vegetation or fine spawning mops as alternative sites. The fish do not guard the eggs, so the cool-water change is repeated daily until a spawn is achieved and the eggs are then managed by the keeper.

Egg & Fry Care

After spawning, remove either the adults or the eggs; eggs deposited on the glass can be gently rolled up it with a finger and transferred. Many breeders add methylene blue, or an alder cone or two, to the rearing container to prevent fungal growth on the developing eggs. Incubation is normally 3-4 days. Once the fry have fully absorbed their yolk sacs they accept small live foods such as microworm and Artemia nauplii, and they do best reared over a thin layer of sand rather than in a bare-bottomed arrangement.

Common Challenges

Egg fungus is the main risk, addressed with the anti-fungal additions noted above and clean water. Adults will eat the eggs if left with them, so separating either the eggs or the spawners promptly after spawning is advised, and a male-biased group helps ensure that ripe females are fertilised.