Should I buy it?
Assassin Snail
Anentome helena
Also known as: clea helena, snail-eating snail, bumblebee snail
A snail you hire rather than keep. Two or three grind a pest-snail plague down to nothing inside a couple of months — then the job is done, and the tank needs a plan for the workers.
Assassin Snail tank mates · 30L tank size hub
peaceful · beginner care
Sources & confidencemedium · partially verified · beginner: good
Typical care sources — real tanks still vary. Numbers here are a careful starting point. Your tap water, tank size, and habits decide the rest. How we evaluate.
Best for: Tanks with an active pest snail infestation where permanent snail stocking is not the goal.
Avoid if: You want to keep nerites or mystery snails long-term. Once pest snails are gone, assassins target any remaining snail species.
Common mistakeAdding assassin snails to a display that already has nerites, and leaving them after the bladder snails are gone, is how keepers lose the valued snails next. Assassins do not clock out when the pest job ends. Remove them after clean-up, or accept risk to ornamental snails and shrimplets. The mistake is treating a predator as a temporary filter you can forget.
Top things that go wrong
- Mouth gap vs tiny tank mates. May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
- Shrimp & snails. Will eat small pest snails on sight; threatens shrimplets, small nerites, and small mystery snails. Not compatible with a working invert clean-up crew.
What most shops don't tell you
- 1.Shops sell assassins as a friendly clean-up crew that only eats pest snails. Once pests run out, the same mouth parts work on small nerites, mysteries, and shrimplets. They work — at a snail’s pace — and they do not read your packing list. Buy them for a planned pest clear with an exit strategy, not as permanent décor beside a prize nerite colony.
- 2.Bought as a generic snail clear-out and left in after the job is done. With no pest snails left, an assassin will turn on shrimplets, nerites, and small mysteries.
- 3.Added to a shrimp colony to clean up dead shrimp. The assassin learns shrimp are food and the colony stops growing.
- 4.Bought as pest snail control for ramshorn or MTS infestations. They work. A pair in a 60L can take a heavy pond-snail problem down to zero in a month. The catch is once the pest snails run out, an assassin will go for shrimplets, leftover food, or starve.
About this species
Assassin snails are small predatory snails from Southeast Asia. They bury in sand during the day and hunt other snails at night, killing small pest snails first. Despite the carnivore tag, they ignore fish entirely and only sometimes harass adult shrimp.
- Blue Dream Shrimp20L min · same group, comparable tank size
- Ghost Shrimp40L min · same group, comparable tank size
- Malaysian Trumpet Snail20L min · same group, comparable tank size
- Bamboo Shrimp80L min · same fish family
- Beckford Pencilfishalso beginner peaceful, similar tank size
- Black Neon Tetraalso beginner peaceful, similar tank size
- Bloodfin tetraalso beginner peaceful, similar tank size
- Blue Dream Shrimpalso beginner peaceful, similar tank size
- Cherry Barbalso beginner peaceful, similar tank size
- Corydoras Catfishalso beginner peaceful, similar tank size
No reverse lookups listed yet.
Plan grid
Key limits are above. Here: pH band, swim level, bioload, and activity.
Swim zones
Care snapshot
Quick compare before you buy. Not a score of how “good” the fish is.
- Beginner ease78
- Peacefulness58
- Community fit23
- Small-tank fit100
- Hardiness76
- Energy24
Numbers are deterministic planning indices from Fishori fields — not a scientific score of your individual fish.
Example setups
Starting points only. Run the pair checker for every fish you add.
Rough 90L+ layout: one calm centrepiece, 8–12 small tetras/rasboras, 6–8 corydoras-type bottom fish — verify every name in the pair checker before buying.
Safer directions include: Cherry Barb, Harlequin Rasbora.
Compatibility
Tank mates for Assassin Snail
Usually safer (engine GOOD): Cherry Barb, Harlequin Rasbora. Conditional (CAUTION — read the pair page before buying): Amano Shrimp, Cherry Shrimp, Corydoras Catfish, Neon Tetra. Avoid (RISKY): Mystery Snail, Nerite Snail. Every name links to a live pair check — the lists are a shortlist, not a stocking plan.
Usually safer
Open a pair page with this fish as the starting point.
Needs planning
Read the blocking rule on each pair page before experimenting.
Usually avoid
Do-not-stock combinations on conservative hobby rules.
Compare with
Run a real pair check: Assassin Snail + Cherry Barb
Behaviour and temperament
Assassin snails are slow predators that spend long stretches buried after a meal. A snail missing for three days is often digesting, not dead. Peaceful toward fish; the predatory tag matters for other snails and shrimplets once pest numbers drop. Daily activity level is a poor health meter for Anentome helena — empty pest shells in the sand are the better census.
What sets them off
- Sudden crowding
- Poor water quality
Fin nipping: Not a habitual fin-nipper; stressed or crowded individuals can still test fins.
Predation: May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
Territory: Not strongly territorial, but still needs room so its working space does not overlap the next fish.
Planted tanks: good — easy plant ideas
In the glass: typical and warning signs
- Long buried rests after meals; empty pest shells appear days later.
- Slow hunting along sand and hardscape, not constant glass cruising.
- Extended burial with no empty shells and no offered food after pests are gone.
- Predation on pest snails first, then smaller ornamental snails and shrimplets.
- Nerites disappearing after pests vanish → remove assassins or accept losses.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Water, food, and grouping
Hardness
medium-hard
Diet
carnivore
They hunt live snails first and still need meaty foods when the pest population collapses — sinking carnivore wafers, frozen foods, or blanched protein. A tank that looks “clean” of bladder snails is when assassins start looking at nerites and shrimplets. Do not expect them to thrive on leftover plant matter alone. If shells stop appearing and the assassins stay buried for weeks, offer food on purpose.
Shrimp & snails
Will eat small pest snails on sight; threatens shrimplets, small nerites, and small mystery snails. Not compatible with a working invert clean-up crew.
Two or three for active pest control in a 60L. More than that in a small tank wipes the food supply and the assassins starve.
- An exit plan. Once pest snails run out, the assassins need re-homing, supplementary feeding, or a tank without small shrimp.
- Sand substrate. Assassins bury during the day. A bare or gravel tank stresses them.
- Confirmation that you do not also want to keep nerites, small mysteries, or a breeding shrimp colony long-term.
- Tank volume meets or exceeds 30L published minimum for adults.
- Heater can hold 20–28°C without cooking cooler-water tank mates.
- No tank mates small enough to fit the adult mouth gap for this species.
Explore and stocking hubs
Tank-mates hub, matching guides, category peers, and litre stocking lists around this species’ minimum tank.
Plan with tools
Check mates as pairs first, then add this fish in the tank builder for the full stocking.
Filtration & heating
A 30L minimum tank needs a filter rated for at least 120L/hr turnover and a heater to hold 20–28°C reliably.
Plant suggestions
Assassin Snail does well in planted tanks. Plants compatible with 20–28°C and pH 7–8:
Research: partially verified · Confidence: medium · 2 linked source(s). We do not invent citations.
How Fishori evaluates compatibility (same logic as pair and tank tools).
- Seriously Fish. Anentome helena
Primary: species page covering range, predatory feeding, and breeding behaviour (lays single eggs, slow reproduction).
- Aquarium Co-Op. Assassin Snails for Pest Snail Control
Secondary: retailer guide on stocking density for pest control, target snail species, and shrimp-safety caveats.
Evidence notes
- Assassin snails do not breed in plague numbers. They lay single eggs on hard surfaces and reach adult size in six months or so, which keeps the population from collapsing the food supply.
- Shrimp safety is conditional. Adult Amano and cherry shrimp are usually ignored, but moulting shrimp and shrimplets are vulnerable in tanks where pest snails have run out.
Featured compatibility checks
Curated pair pages for Assassin Snail. Each opens a full verdict — not just a list label.
Common questions about Assassin Snail
- How big do Assassin Snail get?
- Assassin Snail adults reach about 2.5 cm. Shop fish look smaller; stock for the adult length.
- What size tank does Assassin Snail need?
- 30L is the planning floor for adult swimming space and bioload. A 40L+ tank is the more comfortable long-term footprint. Length and depth matter as much as raw litres for active or territorial fish.
- Are Assassin Snail aggressive?
- Assassin snails are slow predators that spend long stretches buried after a meal. A snail missing for three days is often digesting, not dead. Peaceful toward fish; the predatory tag matters for other snails and shrimplets once pest numbers drop. Daily activity level is a poor health meter for Anentome helena — empty pest shells in the sand are the better census.
- What is the most common mistake with Assassin Snail?
- Adding assassin snails to a display that already has nerites, and leaving them after the bladder snails are gone, is how keepers lose the valued snails next. Assassins do not clock out when the pest job ends. Remove them after clean-up, or accept risk to ornamental snails and shrimplets. The mistake is treating a predator as a temporary filter you can forget.
- What fish can live with Assassin Snail?
- The Assassin Snail profile lists Cherry Barb, Harlequin Rasbora among its safer pairings (engine-checked GOOD). Amano Shrimp, Cherry Shrimp, Corydoras Catfish, Neon Tetra are conditional (CAUTION): workable only with the specific conditions on each pair page. Avoid Mystery Snail, Nerite Snail (RISKY). Run the pair checker for your exact water and tank size before stocking.