Breeding Corydoras

General info

The breeding can be divided in the following general steps:

• Selection
• Sexing
• Conditioning
• Triggering
• Spawning
• Hatching
• Raising fry

Selection of fish

Only breed on healthy animals. Here are some points to look at:

• Barbels, should be long, pointed and most often white or pale, NOT eroded. See Substrate on the Tank page.
• Active fish with erect dorsal fins and fully spread tails.
• Make sure you have both sexes!
• No hollow bellies or sunken eyes.
• Make sure you have both sexes!
• If you can get fry from someone who has bred the species it´s often easier to breed them than wild caught specimens.

Usually use one female and two males. If you have more females and only one is interested in spawning, the other could be spending it's time eating all the eggs that the other is producing. The same goes if you have more than two males, the once that are not actively taking part in the spawning could go caviar hunting instead. If you are using only one male he might not be interested, and I feel that using two males makes them more competitive, chasing the female and getting her in the right mood too.
Note that some males of territorial species such as Scleromystax barbatus and other large long-snouted species might fight and kill each other if the tank is too small. The male could also kill the female if she can't hide from his courting.

Sexing Corys

To be able to breed your fish you need to be sure that you have both sexes present! Might sound very basic but I've tried to spawn Corydoras panda where the difference is not that obvious. I got a lot of eggs but none of them hatched since all three were females.

A sexually mature and conditioned female is always rounder than the male when seen from the side and from above.
When the fish are freshly imported they are NOT conditioned and it can be very tricky to tell the sexes apart. Buy 5-6 fish, if financial status allows, which usually gives you at least one of each sex.

A few of the species have very marked sexual dimorphism, where the male usually has the brighter colors, more markings in the ventral (goes for many of the species) and dorsal fins. This is especially true for the elegans-group (wedge-headed) and Scleromystax (i.e. barbatus).

The ventral fins on the male is often more pointed and with a straighter rear edge. The female has a round rear edge. I will make some drawings later to show the differences.

In some species the male has a more pointed and elongated dorsal. This also goes for the pectoral fin, at least for Corydoras cervinus, where there is very little difference in the other fins.

A post on Planet Catfish about Sexing Corydoras by Ian Fuller.

A good picture of male and female C. araguaiaensis at Planet Catfish

Conditioning them for spawning

The easier species to breed, such as C. paleatus and aeneus, will often spawn if fed only flake food and pellets, but the trickier ones need live or at least frozen food.
You can condition males and females together and move the females that get round to a separate tank together with the males for spawning. You can also separate the sexes and feed the females very well without the risk of them spawning when you are not prepared. (I've had a single female C. sp. "Peru gold-stripe" and imitator spawn on their own though.)
I usually condition my fish with the following live food: grindal, white, and micro worms, also newly hatched brine shrimp.
For frozen I use white and black mosquito larvae (I'm allergic to the red so I can't use them anymore which is a shame), cyclops, adult brine shrimp, and my own shrimp mix.
Apart from the above I use a pellet that's used in professional rearing of salmon or catfish.
Simply stuff as much food in the tank as they eat within half an hour. If you have a sand bottom in the breeding tank it's easy to see when they have finished eating or if you should siphon the leftover food out. Feed several times a day if possible, and of course change water to keep a high water quality.

Triggering them to spawn

Often the biggest problem when it comes to the problem species. You could feed them well and the female looks like a meat ball with fins, but no spawning. There is something missing to trigger the spawn.
Some, like C. aeneus and C. paleatus, you only have to feed well for them to spawn. Other species need a lot more tweaking before they will spawn. All of the species come from a part of the world where there are marked rainy and dry seasons or summer/winter. So trying to simulate as many of the differences as possible is a good idea when you want your fish to spawn.
One of the easiest is to change a large portion of the water with fresh, cold water so the temperature is lowered rather drastically. You can also add peat, increase/decrease the flow/air in the tank. I've written an article that you find below about simulating the rainy season in a tank. I've tried to list all the different triggers I have found in literature and on the net.
The article also outlines how you should set up the tank for successful spawning.

Simulating rainy season in your tank, by me.

Spawning

I will describe the spawning later on.

Hatching the eggs

Can be a tricky part. This is how I do it and it often gives me 90-95% hatch rates even from tricky species such as S. barbatus.

• I always take out the eggs. Some parents will eat the eggs when they have finished spawning. It's also harder to use methylene blue in a tank, it's a very strong dye. The fish usually spawns several times once they have started. Taking out the eggs usually never bothers them. I've taken out C. cervinus eggs from one side of a big lump of Java Moss while they were spawning on the other side of the lump!
• Put them in small containers (2 l/0.25 gal) with 10% water from the tank. I then add drop by drop water from a small container that holds 90% RO water (reverse osmosis) and 10% treated tap water. Use HEAVY aeration for the first 2 days. I use the equivalent of one small air pump with one outlet for one or maximum two of these containers!
• I used to add one or two drops of methylene blue to the water to reduce fungousing. I don't any more. I use Alder Cones instead. See below. 1 or 2 large cones per container.
• Take out 80-90% of the water daily and add back water with the right temperature. Eggs that turn white should be siphoned off at the same time if possible. Some species clump all their eggs together and are impossible to separate.
• When you see that the eggs are turning darker decrease the air flow to a trickle so the newly hatch fry don't have to struggle against the flow.
• When they start to hatch, siphon of old egg shells and debris and continue the 80-90% water change.

• After 1-3 days they will start to swim about looking for food and I some times feed for one or two days in the small container before I move them.

Alder cones etc.

Here's a link to Wikipedia: Alder.

You should harvest them a couple of weeks after the first frost so they drop their seeds.

Will expand on this to talk about different types of leaves etc.