Gambusia (anti-mosquito fish)
Small freshwater fish used to control mosquito larvae. Rustic and prolific, it also lives in stagnant waters.
Detailed explanation
Gambusia (G. holbrooki, G. affinis) has been introduced worldwide as a biological control of mosquitoes. In Italy it is present in canals, ditches and ponds.
It is an extremely rustic livebearer (like the guppy): it tolerates temperatures from 5 to 35 degrees, stagnant waters, low oxygenation, variable salinity.
In aquariums it is not very aesthetically appreciated but it is very useful in ponds for mosquito control.
Warning: Gambusia is aggressive with long-finned fish (guppies) and can become invasive if released into the wild. It is considered one of the most harmful invasive species in the world.