In temperate zones, many of the livebearers seen in home aquariums can be bred in summer in garden pools and ponds. The Mollies are particularly suited to this and produce extra-fine specimens as long as the water is reasonably warm. In a good pool, they will survive at 60F quite comfortably but will not breed unless at about 65F to 70F. It is a custom in many fish-keepers families to place Mollies out in the spring and to net out the proceeds in the fall. A small pool of some 450 to 500 gallons will yield 1,000 young from a stocking which contained perhaps 10 adults 6 months previously. The pond must be protected from predators like birds and even cats, but smaller enemies such as insect larvae fail to keep up with the Molly production line of fry. A great advantage to fish like mollies swordtails and guppies is they have a ravenous appetite for mosquito larva!
Swordtails, Platys and Guppies can similarly be bred in outdoor ponds but the average temperature must be warmer first. These Mexican and Central American native fish do not take to chill as readily as the Molly. However, there is not noticeable improvement with outdoor breeding like there is with the Molly, which produces better, larger and more exotic fishes when pond bred and raised. It is even alleged that Sail-fin Mollies only produce a worth-while crop of Sail-fin young when bred out of doors in the summer; “I have personally experienced amazing success with Sail-fin Mollies in summer ponds, and have never raised an impressive specimen indoors” Remarked Dr. Thomas R. Reich an Ichthyologist that specializes in freshwater aquarium fish.
To some extent, most tropical aquarium fish can be acclimatized to lower temperatures outside than they can survive inside, but they must not be suddenly subjected to lower temperatures. To the same extent, when the fishes are brought in again at the arrival of fall, any necessary rise must be gradual, and the best plan is to use water from the pond in which the fishes have been kept, gradually replacing it with other water, until you have acclimated your pond fish fully to indoor water and conditions. This is, in fact, how most of the fish you buy in your local tropical fish store are raised. They are bred in large outdoor pools in Florida and other areas of the world, raised in these outdoor pools and then acclimated to indoor aquarium water, before they are shipped to your local pet store.
Stocking your garden pool or fountain with live-bearer fish like Mollies, Guppies and Swordtails can be infinitely more interesting, gratifying and ultimately even profitable than the standard 5 or 6 Goldfish or expensive Koki. They may be attractive fish but they do not eat mosquito larva or algae for the most part, which is the norm for the fish we have been talking about, in fact their favorite foods. The activity of the Live-bearers darting about and the constant emergence of new life through the pond can be a joy for the whole family, and virtually maintenance free. The fry eat the natural Infusoria and green water and the adults eat the mosquito larva and other water creatures, which means only occasional feeding is necessary. At the end of the summer, you will be surprised at the fine specimens you have created!