Descripción
Legal warning first: the genus Pomacea is on the list of invasive alien species of Union concern in the European Union. That means that in Spain and across the EU its sale, keeping, breeding and transport are prohibited. The restriction followed the damage caused in the rice fields of the Ebro Delta, where the apple snail established itself from 2009 and devastated crops.
This profile is informational: if you are in the EU you cannot legally keep this species, and if a shop offers it to you they are breaking the rules. Since regulations change, always verify the current situation before assuming anything.
That said, and for readers where it is legal: the mystery snail is the large aquarium snail par excellence. Its shell reaches 5 or 6 cm, it comes in yellow, blue, purple and brown, and it has a presence no other snail matches.
Its most interesting trait is that it does not devour healthy plants, unlike other Pomacea such as canaliculata, which do and are responsible for the agricultural disaster. Bridgesii only attacks leaves already decaying, which made it safe in planted tanks.
It breathes through a siphon it extends to the surface like a tube, so it needs a few centimetres of air between water and lid. A tank filled to the brim drowns it.
Legal alternatives in the EU: if you want a large, showy snail, the zebra nerite or horned nerite cover the cleaning role, and for size the Sulawesi Tylomelania is an unrestricted option.
Hábitat
Pomacea bridgesii is native to the Amazon basin: slow, warm waters with abundant vegetation, subject to seasonal flooding.
That seasonality explains its most striking trait. Pomacea lay out of the water, in pink capsules stuck to glass or decor above the waterline, protecting the eggs from aquatic predators. It is uncommon behaviour and highly visible, and also why the species colonises so effectively: the clutch survives even if the level drops.
And there lies the root of the Ebro Delta problem. The same strategy that makes it fascinating in an aquarium makes it an extraordinarily effective invader in a rice field.
As for care, it needs hard water and calcium. With a 5 or 6 cm shell, the amount of calcium carbonate it must build is enormous compared with a nerite, and in soft water the margin grows brittle and scarred, marks that remain for life.