Assassin snail

Quick facts

Adult size

2.5 cm

Lifespan

can live up to 2 years

Tank zone

bottom

Temperament

peaceful

Difficulty

intermediate

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

22–28°C

pH

7.0 to 8.0

Hardness

8 to 25 dGH

Tank requirements

Minimum volume

40 L

Minimum length

40 cm

Flow

low

Lighting

any

Substrate

sand

Feeding

Diet: carnivore, feeds primarily at the bottom.

Hunts pest snails (bladder, ramshorn, MTS). When prey runs out, will accept frozen bloodworms and high-protein sinking pellets, but populations decline without snail prey.

Compatibility

• Natural solution to pest snail (ramshorn, bladder, MTS) overpopulation. 2-4 assassins clear a heavily infested 75 L tank in 2-3 months
• Will not touch healthy mystery snails, nerites, or other large snails with operculums sufficient to seal the shell. Smaller individuals can sometimes be at risk
• Reports of attacks on baby shrimp are mixed; most experienced keepers report cherry and amano shrimp are safe with assassins, but extra-large assassins have been observed catching slow weak shrimp
• Breeds slowly and lays eggs singly; population can't outpace food supply. Won't overrun a tank the way pest snails do
• Substrate must be fine sand or fine gravel; assassins burrow during the day and emerge to hunt

Habitat

Native to Southeast Asia (Malaysia, Thailand, Indonesia), found in slow rivers and lakes with sandy or muddy substrates. The distinctive bumblebee-striped shell (dark brown and cream-yellow bands) makes them easy to identify. Introduced worldwide through the aquarium trade as a biological control for pest snails (Physa, bladder snails, ramshorns). They hunt by burrowing under the substrate and ambushing prey snails from below.

Breeding

Breeds slowly in aquariums. Sexes are separate (not hermaphroditic like many snails) but impossible to tell apart visually. Pairs mate for hours, then the female buries a single egg capsule in the substrate. Eggs take 4-8 weeks to hatch depending on temperature. Population growth is much slower than pest snails, so they rarely become a problem themselves. Buying 5-6 gives a reasonable chance of getting both sexes.

Common problems

They do not eat algae or detritus. People buy them expecting a cleanup crew, but assassins are pure carnivores that eat other snails and leftover meaty food. Once pest snails are depleted, they need supplemental feeding (sinking pellets, frozen bloodworm). They burrow in the substrate and disappear for days, which alarms new owners, but this is normal hunting behavior.

Bioload

Bioload coefficient: 0.1 (small carnivorous snail; population stays low because food is limiting).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

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