If you get true mosquito fish, not "guppies" sold by pet stores, they will do very well outdoors in your climate. In california, you can get them free from the county mosquito abatement district. They don't care about the size or what's in your pool, puddle, or pond, they will come and put some mosquito fish free in to ensure the control of mosquito larva. The fish will breed and populate from there quite quickly.I had rosy minnow bought from PetSmart years ago. They spawn more than my goldfish ever would. I went from 12 to maybe 500 population. If only I can keep guppies year long like that! But I don’t live in tropical climate.