Pomacea diffusa

Native to South America, the Mystery Snail (Pomacea diffusa) is a fascinating gastropod that has adapted well to the home aquarium. In its natural habitat of slow-moving streams, swamps, and ponds, it developed key survival traits that are observable in captivity. One of its most notable physiological features is a dual respiratory system, consisting of both a gill for underwater breathing and a lung paired with a respiratory siphon. This allows the snail to draw atmospheric oxygen from the surface, a behavior frequently seen in tanks, especially in water with lower dissolved oxygen levels. This adaptation also influences their reproductive strategy.

As a detritivore, its primary ecological function is to clean. It continuously grazes on detritus, soft algae, and biofilm covering all surfaces. While they are excellent cleaners, their diet in an aquarium must be supplemented to ensure proper health and shell integrity. Foods rich in calcium, such as specialized sinking wafers and blanched vegetables like zucchini and spinach, are essential for strong shell growth. A lack of calcium can lead to thin, pitted, or cracked shells.

These snails are relatively sedentary, with a low metabolism and oxygen consumption rate. However, they produce a moderate amount of waste for their size, contributing a noticeable bioload to the aquarium's ecosystem, which should be factored into filtration and maintenance schedules. Despite being solitary, they are entirely peaceful and show no aggression towards tank mates, though they may be preyed upon by larger, aggressive fish. Their tendency to explore can lead them out of the water, making them known escape artists. A well-fitting aquarium lid is crucial, not only to prevent escape but also to provide the humid air space they require for breathing and laying eggs.

Pomacea diffusa, a member of the Ampullariidae family, is a freshwater gastropod mollusk originating from South America. Its taxonomic status is validated, distinguishing it from other closely related species within the Pomacea genus, which are often collectively referred to as apple snails. Morphologically, P. diffusa is characterized by a globiform, or globular, shell. The shell coils to the right (dextral) and features distinct, rounded whorls with indented sutures. A key anatomical feature is its operculum, a proteinaceous 'trapdoor' that seals the shell aperture, protecting the snail from predators and desiccation.

The species exhibits a remarkable physiological adaptation for respiration. It possesses a ctenidium (gill) for aquatic respiration and a pulmonary sac (lung) for aerial respiration. To breathe air, the snail extends a snorkel-like siphon to the water's surface, allowing it to inhabit environments with fluctuating dissolved oxygen levels. This bimodal breathing is a significant evolutionary trait of the Ampullariidae family.

Ecologically, P. diffusa functions as a detritivore and primary consumer. It feeds on periphyton, biofilm, decaying organic matter (detritus), and macrophytes, contributing to nutrient cycling within its aquatic habitat. In an enclosed system like an aquarium, its bioload factor is moderate, reflecting a medium waste output relative to its low metabolic rate. Its IUCN Red List status is listed as 'Data Deficient' (DD), indicating that there is inadequate information to make a direct, or indirect, assessment of its risk of extinction in its natural range. This highlights the need for further research into its wild populations and ecological pressures.

Breeding Mystery Snails is considered to be of moderate difficulty and provides a rewarding educational experience. Success begins with ensuring you have both male and female snails, as they are gonochoristic (having separate sexes) and not hermaphroditic. Sexing these snails visually is very challenging for the hobbyist, so the most reliable method for breeding is to start with a group of at least three to five individuals to increase the probability of having both sexes present. There is no specific ratio required for successful breeding.

Unlike many aquatic snails, Mystery Snails lay their eggs above the waterline in a distinct clutch. For this to occur, the aquarium must have a few inches of open-air space between the water surface and the lid. A female ready to lay her eggs will leave the water, typically at night, to deposit a cluster of eggs on the glass or lid. The clutch is soft and pale when first laid and will harden and darken over the next day.

It is crucial that the egg clutch remains moist but not submerged. The high humidity in the space above the water is typically sufficient for proper incubation. Submerging the clutch in water will drown the embryos. Over several weeks, the eggs will develop, and you may begin to see tiny snails inside. When ready, the baby snails will hatch and make their way down into the water. No intervention is needed for the hatching process. Once in the water, the hatchlings will immediately begin to forage for food. They are self-sufficient and will consume the same foods as the adults, though in finer form. They thrive on biofilm, soft algae, and powdered snail foods or crushed sinking pellets to ensure they receive adequate nutrition for healthy shell development.