Goldfish in Water Troughs for Natural Mosquito Control
How Does it Work?
Female mosquitoes like to lay their eggs (about 100 to 300 at a time) in a dark spot in still water. The eggs then float on the surface of the water for about 48 hours before hatching into larva. The larva will live in the water for about 10 days eating tiny plants and animals. It then changes into a pupa that floats on the surface of the water for about two days before the adult mosquito emerges. Source
The goldfish feed on the larva before they get a chance to mature, which can greatly diminish the mosquito population without any chemicals or pesticides. This also keeps the fish full and happy all summer long, no feeding required! Just remember to top up your water trough regularly (which you probably already do), and check on them to remove any dead fish or debris. Some of mine have lived over 2 years and do well over the winter feeding on algae, plus hay and grain that my horses drop in. I use a tank heater to keep the water from freezing, but they've even survived a few "heater malfunctions" and are surprisingly hardy.
If fish aren't your thing try these Mosquito Dunks. They're organic, pet safe and last for about a month.