Gambusia affinis, called mosquito fish. They eat mosquito larvae as fast as they hatch from eggs. Mosquito fish are furnished without charge for stocking ornamental ponds, unused or "out-of-order" swimming pools, and animal water troughs. They should never be placed in any natural habitat, such as: lakes, streams, rivers, creeks, etc. They require no feeding and care is limited to protecting them from garden sprays and from chlorine or other chemicals used to clean the pond. Mosquito fish do not lay eggs, but rather give birth to live young. These fish, therefore, require no special environment, as most other fishes do, for depositing and hatching the eggs.
They breed throughout the summer and new broods are produced at intervals of about six weeks, with 50 to 100 young in a single brood. The young are approximately 1/4 inch in length when born. They are ready to begin the work of destroying mosquito larvae at once. Gambusia grow rapidly, reaching a maximum size of about three inches. The earliest brood of the season, born in April and May, become sexually mature and produce young when six to eight weeks old.