Rosy Barbs are egg-scatterers. That means the female drops the eggs and the male fertilizes them at the same time. In a community tank the eggs will be quickly eaten -- if you are serious about breeding these fish you should set up a small 3-5 gallon tank just for a pair of Rosy Barbs to breed. If you would rather not go through the trouble, then you might want to breed Swordtails. They are a lot easier.
Tank Setup:
A 3 gallon or larger will do for breeding and the raising of fry. There should be lots of plants (fake ones will work also). It is preferable to have an undergravel or sponge filter -- if you have a mechanical or biowheel you have two options, or else it will suck the fry up. First, you can cover the intake with something that will not allow fry to pass through. I have heard that pantyhose works well for this. Second, you can turn the filter off. This is not recommended if you don't have a pump and airstone to create surface agitation (keeps oxygen levels high).
Water Chemistry:
Ammonia: This must be at 0. It will be if no other fish have been in the tank.
pH: Rosy Barbs are not very sensitive to pH. 6.5-7.5 will be fine, and it might even work outside that range.
Water hardness: Rosy Barbs like soft water.
Introduction of parents:
The parents must be fully matured, and you should have had them in your main tank for a while. The female might look fat (from having lots of eggs in her), and have a pinkish color. This means that she is probably ready to mate. Put her in the tank a few days before you put the male in. This is to allow her to get acclimated to the new tank and water conditions-- unlike the male, she won't breed if under stress.
After one through three days, assuming she is doing fine, add the male. Hopefully they will lay eggs over the next few days, and they will nearly always do it in the morning.
Laying Eggs:
In the morning the male should start chasing the female around the tank. If he can push her against plants and such, then she will lay eggs. The whole breeding process take three hours or so, with 100-300 eggs being laid. Some will be eaten even if you put marbles in the tank-- but you really don't need 300 fry, right?
The eggs are about the size of the period on your keyboard. They are clear. If they become white, they are most likely infertile-- there is no need to remove them, though. After a few hours, when it looks like they are done laying, remove the parents.
Hatching:
Okay, now you have got all the eggs safely in their own tank. For the next two or three days, there isn't much to do. The eggs should hatch from 24-72 hours. The fry will attach themselves to the glass, and won't swim much at all. You should begin feeding a bit now. Soon, they will become free swimming, and will zip around the tank.
Feeding:
I feed my fry ground up flakes. It does work, although it's probably better to feed live foods (often not available at pet stores). If you use flakes, use a mortar to grind them up really finely, into a power. Feed as much as you think necessary without overfeeding-- use your judgment.
Oh, and when the fry are really tiny (right after they hatch) it will be helpful to add decorations, plants or algae clumps from your main tank. There will be micro-organisims on these things, and the fry will often be able to eat them.
Free-swimming stage:
Most of your worries are over now, if the fry are eating. Fortunately, Rosy Barbs, even as fry, are really hardy. There will most likely be few casualties.
What to do with them:
You probably won't be able to keep most of your fish once they start getting big. How can you get rid of them? And when? The best way to go about it is to give them to your pet store-- they might even give you a bit of money in the form of store credit. You have to decide when to do it, mostly depending upon how well your tank can hold them now. Wait until they are at least half an inch long, though, and preferably bigger. Otherwise, they may not survive the stress of traveling and the new conditions. And, remember to keep some for yourself!
Part or all of the tank bottom should be covered with marbles instead of gravel, as this prevents the parents from eating them.
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