Guppy Fry Care:
If you decide to raise the young fry, consider setting up a few tanks to let the fry grow out in. Start any tank immediately, before the young ones arrive so the tank can cycle before the fish are added. Do this "fishless cycling" either by ammonia cycling(adding 3 drops of ammonia per day until nitrite forms), or by taking water from your existing tank and filling the new tank with all siphoned debris and water. The debris starts the ammonia which starts the cycling, and any water provided from the existing tank will have some nitrifying bacteria already in it providing a quick start for the nitrogen cycle. If possible, exchange filtration m media from an existing tank to the new tank so the process will be expedited.
In the fry tank, you'll need to cover any suction devices with a material to stop fry from being sucked in to filtration. I suggest you find some fine bridal netting or tulle and cut a piece to cover suction tube and hold in place with a rubber band. Some suggest using nylon pantyhose, which you can use until you find netting, but I don't suggest using it all the time as it will interfere with filtration process. The fry tank can be a simple tank, meaning all you'll need to provide is filtration, heating and lighting. I don't have any type of gravel in my fry tanks as this allows very easy cleaning of the tanks. As the fry mature and are separated, then I place gravel and plants in larger tanks for them to continue growing. Set the temperature to 80F if possible to allow maturation and then as the fry age, you can reduce the temp back to 78F.
After the new tank has cycled when levels are ammonia zero, nitrite zero, and nitrate is 40ppm or less, then you can add the fry. You'll need to feed the fry a few times per day. If possible for the first four weeks feed them as often as time will permit. Some feed the fry 5 times per day. The first four weeks of their lives go into building body and muscle tone. Grind the tropical flake food to powder to feed the fry. It would be great if you're able to hatch brine shrimp to feed the fry a couple times per week. The baby brine shrimp provide a great source of nutrition to enhance fry coloration. Don't use color enhancing flakes as the flakes don't provide correct vitamins the fry need to grow properly.
At the end of the first four weeks, the fry begin to sexually develop into male or female guppies. At the age of 6 weeks, they become sexually active. So, between weeks 4 and 6, you might want to consider separating the fry into female, male groupings. Do this by taking one fish out at a time and placing in a small container with water from the tank and with a magnifying glass look for either the gonopodium or the gravid spot. More often it is better to see the gravid spot of a female. Mix ups do happen and don't be to worried as the fish can be selected out a put into the correct group. It's just a bit less to worry about what you'll be doing with the fry of all the young females if you decide to separate them.
Between the ages of 6 weeks and 6 months, you'll need to consider putting some of the fry to sleep due to deformities in some of the fry. This is a procedure called culling which means to take out the bad fish. Most stores will take the culled fry off your hands, but don't expect anything in return, as they are doing you a favor. See the page about putting fish to sleep.
At six months of age the guppies are then considered adults. So, you're still going to have to find some one to take them. A donation on your part at this age is considered highly recommendable, but think about all the effort you put into raising the fry. If Local fish stores won't trade or pay you for your efforts, consider asking who their distributor is and get a name and phone number. Check the distributor to see if they'll take your fish. Distributors pay you more money for larger fish. Meaning, if by week 4 the fry are too much to handle, a distributor will take them, but probably only for a couple dollars. But if you wait til they're six months old, you will probably get 50 cents per fish. Same goes for trading or receiving payment from a local fish store. The bigger the better. Remember to check with your area regarding laws.
Good Look with keeping them! Have fun