The Breeding of Corydoras Catfish
A newbies guide
One of the most popular fish that new and experienced aquarists breed is corydoras catfish. People are attached to them because of their fun character, friendly personality, peacefulness, small size, and their ability to clean up food off the substrate. After falling in love with these little characters, for many the next step is attempting to breed them.
There are two different scenarios:
- You find some corydoras eggs in your community tank
This is quite a common occurrence in well kept tanks where the corydoras catfish are well fed and the tank has good water parameters. Let's face it- to breed they must be happy, as they're confident that the young will thrive in the conditions that the tank has. In this situation, skip to how to care for the eggs and fry.
- You want to purposely breed corydoras catfish
This method involves more time, money and tanks than if the first scenario were to happen.
First off, if you want to purposely get your corydoras catfish to breed, then it is highly advisable to set up a corydoras species tank, as other fish in the tank might not be tolerant of the conditions that you could make to help the corydoras want to breed.
The breeding tank doesn't have to be very big, but make sure it has a large footprint (large substrate area) as opposed to being quite a tall tank, you don't want to be investing money in a large tank, when it has the same footprint as a tank with less volume that could have been bought for less money. This is because quite simply, as you will notice, corydoras catfish tend to swim around the bottom of the tank, across and along, and don't use the upper areas very much. You also want to have the water pretty oxygenated in the fry tank, and a large footprint gives more surface area to absorb it.
It has been known for corydoras catfish to breed in a tank as small as 5g, however they would need to only be in there for a short period of time whilst breeding occurs. A tank so small would require a lot of water changes and maintenance to keep the nitrAtes down. As a breeding tank, I would recommend a tank around 10g, obviously with proper filtration and a heater. This would require less water changes and maintenance, and give the corydoras catfish more swimming space, thus most probably making happier corys.
Decoration is down to personal choice, however things such as sand/small rounded gravel substrates and hiding places would be recommended to make that little effort to make the corys happy, which is very important. I would not, however, create too many nooks and crannies as you don't want finding the eggs to be too difficult. A quite important addition you might want to add is a couple of broad leaved plants, since some species of corydoras like to lay their eggs on plants.
Just like keeping them normally, you will need to keep your breeding corydoras catfish in groups to encourage them to breed. It has been known for them to breed in groups of 3, but more is obviously better, 6 is a very good number.
Next up is the fry tank. This will have to be bigger than the breeding tank, as you could be looking at over 100 fry, and all of these will have to be raised by you to a sellable size. A good choice is to have more than one fry setup, upgrading as they get bigger. As a general guide, I would say around 10g or less as a hatchery and to raise the fry in the very early stages, 15-20g as they are a bit bigger, and 30g for when they are coming up to sellable size, the sellable size depending on what lfs you want to sell them to. The reason I recommend more than one is that 100+ tiny tiny fry in a 30g tank, the odds of them getting the small amount of food that you will be adding would be slim.
For ease of maintenance, you may choose not to have a substrate in your fry tank(s). This I would recommend, especially for the tank that will be used very early on, because as I'm sure you can imagine, you could overfeed and there could easily be a buildup of bad bacteria on your substrate, putting your delicate fry at risk.
A method that some aquarists use is to have no substrate and instead smear on some of the residue from a mature filter onto the base of the tank. This residue would contain beneficial bacteria that would help to prevent such a buildup of toxins etc., just the same as your filter removes toxins from the water. As for filtration, in the early stages of development, an air powered, very small sponge filter is recommended. Any big, 'proper' filter would very easily suck up small fry. Obviously as you get confident that they are beyond that risk then you can give them a 'proper', cycled, filter.
Breeding you corydoras catfish
As mentioned earlier, you will not get corydoras catfish to breed if they are not happy with the environment around them, just like any other fish. So, a very important thing is to make sure they are happy by giving them hiding places (not too many as mentioned before) etc. Another very important factor for making them happy is water parameters. There are the obvious ones, no nitrIte, and no ammonia. PH would ideally be around neutral, if not a bit acidic, but this isn't too important to be honest. What is quite important is to keep nitrAtes low. The best corydoras breeders I know have kept their nitrAtes around 10. This means plenty of water changes, depending on tank size.
Now, onto conditioning them to breed. These are the 2 main things: plenty of live food, and cold water changes. Plenty of live food- it's going to make your corydoras catfish happy, and what you want to do is make their environment resemble what would be good conditions in the wild. Blackworms are a very good choice for live food, however this could be hard to find, so bloodworms work well too. In the wild, if there was an abundance of good quality food, the corydoras catfish would be thinking that whilst there is now loads of great food, it is the perfect time to bring more corydoras' into the world! So make sure you feed plenty of it while you want them to breed.
After feeding plenty of live food you will probably notice some interest in breeding. One tell tale sign is that the female(s) get very fat, this means they are filling up with eggs, and you might notice the males showing interest by following the females around a lot and not leaving her side.
Remember to keep nitrAtes low. Now, either you can do a few water changes with cold water if not much activity is going on, just to egg them on a bit, not too large changes, about 20% if you're doing multiple ones, OR, if you see lots of activity (the female could look bigger but this can be hard to tell) then do a bigger cold water change, no more than 40-50% though, and then, you have a chance of waking up to loads of cory eggs!
Pre-spawning activity includes males chasing females (can be the other way round), males 'dancing' to female, so just general interest in the opposite sex. You will see when they are actually fertilizing the eggs because the male and female go into what's known as the T-position, where together they simply make the shape of the letter T.
They lay eggs in different areas depending on what type of cory they are, usually on plants or the tank walls, though they don't usually lay eggs in caves. The female will carry the fertilized eggs to her desired destination and place them there. It is important to realize that while you cannot force corydoras catfish to spawn, you want to simulate the rainy season in the wild; then it's up to the corydoras catfish.
Sometimes, as some of you may know, corydoras catfish breed without you even having to condition them, so these conditions are just things that could help.
Hatching your corydoras eggs
Either the eggs should be removed from all other fish including parents or parents and fish removed from the eggs. This is because there is a risk of other fish eating the eggs, even the parents could snack on them.
The eggs should be placed together on the tank wall or another vertical surface. You will find that the eggs are pretty sticky, and can quite easily be rolled off the tank wall and onto your finger, if you want to transfer them. It is best not to expose the eggs to air, and do remember to be careful when moving them so they are not damaged or even destroyed.
To help prevent fungal growth (which would lead to the eggs not hatching) the eggs should be placed in some kind of water flow. An easy way is to simply place an airstone underneath the eggs.
Fertile eggs will look quite beige in colour, and will develop a darker spot in the middle as hatching becomes near. Infertile eggs will look plain and white/translucent. The eggs should take about 3+ days to hatch, and when they hatch they will be absolutely tiny.
Newborn fry should be fed on foods such as the product LiquiFry. This is a liquid solution of food. A better option is microworms or baby brine shrimp, since these will give more nutrition. As the fry grow, the size of food given can grow too, onto crushed flake and eventually flake and perhaps pellets as they reach a sellable size. As I said earlier, it is important to take care of the water conditions in the tank especially in the early stages, as the fry will be very fragile and intolerant. You should also upgrade tank as they get bigger, but in the end, make sure the tank is around 30 gallons or more.
Daily water changes of say, 20% or more, should always be done and it's especially critical when using LiquiFry or a similar product. This is to prevent harmful bacteria from breeding in there and to help them grow.
Here is a simple equation that I made up for breeding corydoras catfish:
1 tank + a group of corydoras catfish + good water conditions + very low nitrates + live food + cold water changes + general happiness = cory eggs!
Hope this is a helping hand to all those hoping to breed corydoras catfish.