Minnows do not kill your pond, and in fact, can be extremely advantageous to your outdoor water garden's ecosystem. Minnows, like many species of fish, are top-feeders, meaning the shape of their mouth makes eating food floating on the surface the easiest way for them to feed. For this reason, they are voracious mosquito larvae eaters. Additionally, their waste can help fertilise pond plants and they cause minimal damage to plants' root systems and foliage.
Mosquitoes require water to lay their eggs and live out their first stage of life as larvae. Your pond will make an excellent place for mosquitoes to reproduce, and you may have seen their wormlike larvae twisting around just under the surface of the water. When these larvae become adults, some of them will be the females that plague your evenings near the pond. Keeping minnows in your pond can all but eradicate mosquito larvae and substantially reduce mosquito populations in your yard.
Waste as Fertilizer
Minnows eat mosquito larvae and the fish food you sprinkle on the pond surface, and expel waste containing nitrogen and ammonia, among other things. These nutrients can build up in a pond that does not have any aquatic plants, but act as a natural fertiliser in those that do. Keeping minnows in your pond will help feed your plants and encourage their growth, while providing a lively splash of life to your water garden.
As top feeders, minnows are minimally damaging to aquatic plant root systems and foliage. Other fish, such as goldfish and koi, can munch a water hyacinth or waterlily down to its roots in a matter of days. Minnows, however, eat floating food items, and tend not to chew on items beneath the surface, including the roots of your plants. This makes minnows a great choice for a pond with expensive aquatic plants.
Anyone with a pond in a temperate zone has no doubt had to deal with snail infestations. Water snails will eat the root systems of your plants, and then move above the water to finish off the foliage. These aquatic pests reproduce rapidly and can be a real problem once they gain a foothold on your pond. Minnows are voracious snail eaters, and will eradicate these pests before they destroy your pond plants.