Four types of livebearer readily breed in community tanks, and there's plenty of experience for you to draw on if you want to ensure you raise a healthy brood of fish. Guppies, mollies, swordtails, and platies all breed regularly in aquaria with little help from the aquarist. Really, the only thing you need to take care of are the following:
(1) Ensuring that the baby fish aren't eaten
(2) Providing an adequate diet so that the fish grow steadily
Ensuring that the baby fish aren't eaten
Even if the fry survive in a community tank long enough for you to find them, there's no guarantees they won't be eaten by the other fish in the tank. Dwarf cichlids, angelfish, catfish, and barbs may look benign but they will hunt down any livebearer fry that they find. So, it is invariably a good idea to remove the fry to a separate aquarium as soon as possible.
Sometimes the parents will eat their own fry, but this isn't always the case, and guppies and platies in particular tend to ignore their offspring provided they are otherwise well fed. If you want to take the chance of leaving them with their parents, it's a good idea to incorporate some plants into the tank. These will give the fry some cover, and instinctively they hide among the leaves away from larger fish. Floating plants, such as Ceratophyllum demersum are ideal for this.
Breeding traps can be used to create a floating "refuge" in the tank for raising the fry. On the plus side they are inexpensive and easy to use. But they are very small, and usually only make sense with small broods and over the short term. If confined to breeding traps for more than a couple of weeks, fish tend to become stressed. Bottom line, they can be an excellent stop-gap solution but you still want to invest in another tank to raise the fry. Bear in mind that it takes about 3 months for baby fish to get big enough to be combined with generic, non-predatory community fish.
Breeding nets are similar to traps but a big bigger, so allow you to keep the baby fish confined in them for a week or two more. But again, they are stop-gap solutions rather than alternatives to a second aquarium.
If you're keeping the baby fish in a breeding trap or net, float a large leaf or some floating plants inside it. This gives the baby fish some cover, which they appreciate.
A tank for raising fish need not be complex or expensive. I use a 30 litre (~10 US gallon) aquarium, half-filled with water taken from the main aquarium. A heater is obviously essential, but lighting is not, and I usually keep the tank in a sunny place so that floating plants can be grown easily. Filtration is also easy: a simple box-filter powered by a small air pump is ideal. Avoid strong electric filters as these can suck up tiny fish, resulting in their untimely demise.
Providing an adequate diet to that the fish grow steadily
Baby guppies, mollies, swordtails, and platies are easy to raise. Finely powdered flake food is taken readily, and there are commercial baby fish foods (such as Liquifry) that can be used as well. They will also peck at algae and aquarium detritus. Once they become a little larger, frozen foods are an excellent way to speed up their growth, with things like bloodworms being popular and easy to buy.
Feed your baby fish small amounts on a very regular basis, more often than you would feed adult fish; at least 4 times a day, and preferably 6 times a day. Give them as much food as they will eat within a couple of minutes, and remove anything left over.
These baby fish grow rapidly, and you'll be astonished at how quickly they develop. Just as with any other fish, move the babies to larger quarters as they grow. Mollies in particular are rather large fish, and sailfin mollies will not develop their sail-like dorsal fins if kept in crampt conditions.
With thanks to Annastasia
Edited by nmonks, 14 November 2005 - 10:14 AM.