This is one subject that crops up regularly; I will try to give you an easy description of the basics.
Most but not all Corydoras breed in the same manner, there are a few that need more coaxing to get them going but this will give you the basic idea.
The majority of Amazonian fish are triggered into spawning by the seasons of the year. Drought with little food followed by the floods with an abundance of food. This is usually the only stimulus they need to start breeding.
In the aquarium we have got to try and replicate the seasons of the year to induce spawning.
One way of doing this is as follows:
I use small tanks 18" x 15" x 15" for breeding Cory's, Silica sand substrate, 25C with small air driven foam filter, small bunch of Java Moss and Fern are sometimes used.
Select your Breeding stock having 2 males to 1 female.
Feed well on good quality foods such as Brine Shrimp, Bloodworm etc.
After two weeks of this the filter should be starting to slow down, and water movement should be relatively slow.
Gradually reduce the quantity of food but not the quality over the next week, do not clean the filter.
Now remove 50% of the water volume, Clean the filter and refill with water at a temperature of 20-22C.
You hopefully will find lots of eggs stuck firmly to the glass and on any plants present the next morning, remove parents and add 1 drop per gallon of Methylene Blue.
Eggs should hatch in about three days at 26C and should be fed Microworm or Baby Brine Shrimp as first food after they have used up their yolk sac (a further 2-3 days).
Please note this is only a rough idea of the principle.
