Who isn't concerned about mosquito larvae in their horse's water trough? Gross right? Not to mention all those mosquito born diseases. To combat this I utilize goldfish to keep my water clear of larvae. The fish also keep algae down as well. I have had the same fish for many years. They over-winter just fine in my three-hundred fifty gallon tank. The fish eat the grain from the horses mouths when the boys take a drink after eating. One thing I have learned is to move the fish to a different tank after worming the horses. The wormer is toxic to fish if the fish are exposed. Goldfish are a beautiful, fun, practical addition to any farm!