For the past two years, I have put out rain barrels at my house. Two of the rain barrels have no tops, and so I use goldfish in the barrels to keep the mosquitoes from hatching.
Last year the fish went away when I emptied the barrels. This year, I saved the two remaining fish and am attempting to overwinter them with my plants.
It seems that I spent too much time thinking about the fish, however, and not enough time actually emptying and winterizing the rain barrels. Winter has come early, and the remaining water is already frozen in the barrels. I'm really hoping for a few days thaw, or I'm going to end up with some cracked rain barrels come spring.