I found this information online, and thought I should share it with all.
Mosquito Fish
Mosquito fish (Gambusia affinis) are available free to residents of Washington County for use in their ornamental ponds and water troughs. Call the Environmental Health Program at 503-846-8722 for details.
Mosquito fish (Gambusia affinis) are small fish ranging in size from 1 to 2.5 inches. They have been known to feed on spiders, snails, algae, zooplankton, fish fry, and insect larvae.
Gambusia a. received their name “Mosquito fish” because of the large amounts of mosquito larvae they have been known to consume. One Mosquito fish can eat over 50 mosquito larvae in less than an hour.
Mosquito fish are non-native to Oregon and therefore state law restricts their use to self-contained water bodies which are not fed or drained by natural waterways.
Information regarding how to use Gambusia a. for mosquito control is available from the Oregon Department of Fish and Wildlife.
A West Nile Virus Fact Sheet is available from the Oregon Department of Fish and Wildlife.
Happy ponding,
Rich
P.S. Washington County is in Oregon State.