Is Snail Infestation in an Aquarium a Danger to Fish?

In most circumstances, snails do not directly harm anything in an aquarium other than the aesthetics of the tank -- and even this is debatable. However, in some specific situations, they can harm fish, either through compromising water quality or, very rarely, through direct action against fish.

  1. Blooms

    • One of the biggest problems with aquarium snails is blooms. Under the right conditions, aquarium snails reproduce rapidly. Usually, overfeeding the aquarium or failing to keep up on regular water changes can result in a population explosion of snails. While these blooms can cause problems in and of themselves, the most immediate concern is that these blooms occur only when something's wrong in the tank. Overfeeding can lead to problems with ammonia and pH, and a sudden bloom of snails is usually a sign that something is wrong with water quality.

    Dangers to Fish

    • Sudden blooms of snails may represent problems in and of themselves. Snails add to the bioload of the tank, for instance. They use up oxygen and produce waste just like fish. Under normal circumstances, snails don't contribute much to the bioload of a tank. But when snails overrun a tank, they can appreciably strain the tank's water equilibrium. Additionally, these blooms can collapse in on themselves. The damaged water quality can lead to a mass die-off of snails. The rotting snails can further foul the aquarium water quality.

    Scavenging

    • Sometimes, snails get accused of preying on fish. You may see snails feeding on dead or dying fish. However, the vast majority of aquarium snails will eat only a fish that's either already dying or dead. No common freshwater snails will harm a healthy fish, though their propensity for eating dead fish may be mistaken for predation.

    Fish-Eating Snails?

    • A few snails may actually harm fish, but they are restricted to saltwater and are extremely rare in the aquarium hobby. However, live rocks -- dead coral encrusted with other invertebrates -- often contain hitchhikers, which can rarely include cone snails. This snails is deadly, both to aquarium fish and possibly even to humans. If you see a cone-shaped snail in your marine aquarium, remove it with tongs and do not touch it. This type of snail injects venom with a harpoonlike organ that can easily penetrate gloves.