Mystery snail

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Feeding

Algae, biofilm, and decaying plant matter are the primary natural diet. Supplement with blanched vegetables (zucchini, spinach, kale), algae wafers, calcium-rich foods (cuttlebone, snello), and sinking fish food. Mystery snails are not effective algae cleaners compared to nerites; they prefer softer surfaces and biofilm. Calcium intake is critical for shell health. A piece of cuttlebone in the tank dissolves slowly and provides a continuous calcium source. They eat constantly and produce a lot of waste relative to their size.

Compatibility

• Safe with all community fish that don't specifically eat snails. The operculum (trapdoor) protects them from nibbling fish.
• Assassin snails will kill mystery snails. Do not house together.
• Loaches (clown loach, yoyo loach) and puffers are snail predators. Some cichlids will also pick at snails.
• Safe with shrimp. Mystery snails are too slow to catch anything and don't eat live animal matter.
• Will not eat healthy live plants. May eat dying or melting leaves, which is beneficial.

Origin and habitat

The aquarium mystery snail is an apple snail from the Amazon basin, native across Bolivia, Brazil, Paraguay, and Peru. Its naming is a common point of confusion: the snails sold as mystery snails are almost always Pomacea diffusa, which was long treated as a subspecies of Pomacea bridgesii until DNA work showed the two to be separate species. True P. bridgesii is rare in the trade, while P. diffusa is the species kept worldwide. It should not be mixed up with the channel apple snail, Pomacea canaliculata, a destructive crop pest banned from trade in many places that does eat live plants; the mystery snail does not, preferring algae, biofilm, and dead or decaying plant matter, which makes it one of the safer snails for a planted tank. Mystery snails breathe both with a gill and through a long siphon they extend to the surface for air, so the tank needs a gap of open air above the water. They come in several captive-bred colours, with golden the best known, alongside blue and white. The shell reaches roughly 4 to 5 cm across and a little taller.

Breeding

Unusually for a popular aquarium snail, mystery snails lay their eggs out of the water. The sexes are separate, so both a male and a female are needed, and a female can store sperm to lay several clutches from one mating. She leaves the water at night and deposits a pinkish, soft egg mass on the lid, hood, or glass above the surface, and it hardens over a day or so. A clutch holds roughly fifty to two hundred eggs and hatches in about two to four weeks as long as it stays humid but not submerged, after which the babies drop into the water and start feeding. Breeding is easy and numbers can climb fast, so the simple control is to remove clutches before they hatch.

Common problems

Shell health is the main concern. In soft, acidic water the shell thins, goes chalky-white, and can crack, so the water needs enough calcium and carbonate hardness, with a piece of cuttlebone as a slow calcium source. A snail that stays shut up in its shell for long stretches is usually signalling stress or poor water, so ammonia and nitrite are worth checking. Copper is lethal to snails even at fish-safe doses, so copper-based medications are out. The other common, avoidable death is getting stuck in an uncovered filter intake, so a sponge guard is worth fitting.

Bioload

Further reading

• Blackwater tanks: replicating acidic jungle streams
• Medicating a tank with snails and shrimp
• Water chemistry for fishkeepers: pH, GH, KH, and what they mean