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Hi everyone. I'm new here but have been keeping fish for about a decade. Currently I have a bunch of south american cich-lids and a few different types of corydoras and plecos and have no problem getting the cich-lids to breed but have recently decided to try my hand at breeding thier tank mates.

I have a 20L set up by a window that I have has a mature group of 5 corydoras melanistus brevirostris, at least thats what they were sold as and they seem to be the same as the picture in the cat-elog. I think there are three females and two males based on observing where the widest points of their bodies are and the two are also slightly smaller than the others. There is a whisper 20 power filter with a sponge pre-filter on the intake. I have a few fake plants bunched in the corner and a piece of driftwood that fills up about a third of the tank.

Theyve been in the tank for about three weeks now by themselves and just a few days ago I've turned off the heater and started doing cold water changes(I live in South Florida so its still 80 outside) and I've been feeding them chopped earthworm, tubifex, krill pellets, and brine shrimp for maybe two weeks now.

Just today two of them, the two I think are males, have turned a darker color than the other three and I was wondering if this is normal behavior. Theyre still swimming around and eating fine but just a shade darker than the others.

Also, is there anything else that I could be doing to speed up this process?

Thanks,
Bill

I think your fish are

I would recommend reading all the Corydoras spawning accounts in "Shanes World" because you will be able to see a common thread of heavy pre-spawn conditioning of Corydoras on a diet of live worms and then large cool water changes. Often the use of cool RO water works as the trigger for Corydoras to spawn. It may simulate the onset of the wet season when most SA fish spawn. The heavy rains lower the total dissolved solids and cool the waters. Increasing the currents through the use of a large sponge filter connected to a power head and a vigorously bubbling air stone will help simulate increased high water currents and saturated dissolved O2 levels. All of these inter-related conditions may contribute to inducing fish otherwise ready to spawn but only lack some triggering factors.
Do not become discouraged if your Corydoras fail to spawn right away. It may take many repetitions of the above before some species spawn. Although you are feeding your Corydoras a good diet i have found that copious feedings of live black worms are very helpful in encouraging Corydoras to spawn. I keep a constant supply of them in their spawning tank.

I personally prefer to use a thin layer of fine sand, ~0.5 cm at most for Corydoras spawning tanks. The Corys always like having sand to root the live worms out and I also use an acrylic mop or clumps of Java Moss and/or Ceratophyllum. A couple small clean clay flower pots can be added to provide some sense of security for the breeders. The use of a thin layer of sand seems to be helpful in increasing the survival rate of the larval fry compared to the results of bare glass, IME.
I do something a that is different than most Corydoras breeders in that I also stock the breeding/rearing tanks with some Cherry Shrimp. I have never had them harm any good eggs and they do not harm the fry. The shrimp seem to help keep the food cleaned up that the fry miss. Cleanliness is important but the tank should be well established rather than set up and stocked before the nitrogen cycle has become established.

Thanks for the input. Either classification, I like thier patterning and coloration and I'll look more closely at the differences between brevirostris and delphax.

The tank has been set up for a few months now and I moved the rams that were in there previously to a 29 gallon so its long since been cycled. There really isn't much sand in there at all, just enough to cover the bottom of the tank and I've asked the LFS to order some blackworms so those should be in next Tuesday. I've also added an airstone and a powerhead in the corner opposite the power filter thanks to your advice.

It seems after more research that they won't be jumping the gun to spawn so I'm not as anxious for them to get it on right away but I'll keep doing what I can and I'll keep an eye out for some cherry shrimp, but I've only ever seen them once or twice around here.

Again, thanks for the input and I'll keep you all updated.

Keeping Cherry Shrimp in my catfish breeding tanks is something i do but not many others do. I feel they are useful but they are not essential by any means.