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

Native to the Amazon river system in South America, distributed across Bolivia, Brazil, Paraguay, and Peru. The taxonomy is complicated: what aquarists call "mystery snail" is usually Pomacea diffusa, which was long considered a subspecies of Pomacea bridgesii until genetic analysis confirmed them as separate species. P. bridgesii is restricted to Bolivia and the western Amazon basin and is rare in the hobby; P. diffusa is widely distributed and is the species found in the aquarium trade worldwide. The destructive invasive channel apple snail (P. canaliculata) is a different species and is banned from trade in the US and other jurisdictions; mystery snails (bridgesii/diffusa) do not feed on healthy live plants, preferring dead and decaying plant matter and algae. Lay eggs above the waterline, a trait shared among Pomacea species but uncommon among popular aquarium snails. Gonochoristic (separate sexes); a male and female must be present for reproduction. A single egg-laying event can produce up to 200 offspring; eggs take 2-4 weeks to hatch. Population control is simple: remove egg clutches before they hatch. Color variants in the trade include golden (the most well-known), blue, and white, produced through captive breeding. Possess both gills and a breathing siphon for taking atmospheric air; they frequently surface to breathe and need air space above the water line. Lifespan in the wild is reported at 3-4 years.

Breeding

Egg layer that deposits clutches above the waterline. The female climbs out of the water at night and lays a pink-white calcified egg mass on the lid, hood, or tank rim. Each clutch contains 50-200 eggs. Eggs need humid air (not submerged) and hatch in 2-4 weeks depending on temperature and humidity. Baby snails drop into the water and begin eating immediately. Breeding is easy and can quickly result in too many snails if clutches aren't removed. To prevent breeding, simply remove egg clutches before they hatch. Sexing is possible by examining the shell opening: males have a penial sheath visible under the right side of the mantle.

Common problems

Shell erosion in soft, acidic water. Mystery snail shells dissolve in water with pH below 7.0 or KH below 3. The shell thins, develops white patches, and eventually cracks. Maintain GH above 8 and KH above 4 for healthy shells. Calcium supplementation (cuttlebone) helps but doesn't fully compensate for acidic water. Deep retraction (snail stays in shell for extended periods) indicates stress or poor water quality. Check for ammonia and nitrite. Copper kills snails at concentrations safe for fish; avoid copper-based medications. Mysterious deaths are often caused by getting stuck in filter intakes; cover all intake tubes with sponge pre-filters.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size