well i have never owned any but my aunt has ..... She purchased 12 to keep down the mosquito population aroung her small pond in a few months she had a pond full (atleast 100)they are good fish to keep outside in a pond here is a little info on them (hope it helps ):




The Mosquito Fish originates in the backwaters and freshwater ponds of North and Central America. It is an excellent controller of mosquitoes for your outdoor pond. It is in the same family as the common guppy and is very similar in characteristics. The body is long and slender and is pale in color. The tail is moderate in size and does not contain any coloration.
The Mosquito Fish requires a pond of at least 20 gallons with plenty of plants for hiding. These fish are natural to North America as far north as Central Illinois, and will tolerate winter conditions as long as the pond is deep enough and is aerated through the winter.

You can differentiate the male and females easily. The males are smaller in size, have a pointed anal fin and are much thinner than the female. The females are larger in size, have a rounded anal fin, as well as a pregnancy patch on the lower portion of the body. Ideally, the environment should have a covering of floating ferns and a breeding box to protect the fry. Adults may eat the fry if left to fend for themselves without the breeding box.

The Mosquito Fish feeds upon the larvae of mosquitoes and other insects. If insufficient natural foods are present, supplement their diet with a quality flake food.

Approximate Purchase Size: 1-1/2" to 1-3/4"