Photo: Steffi Klee (CC BY-SA 3.0) — via Wikimedia Commons
Assassin Snail (Clea helena)
The aquarium's hired assassin: a striped 2.5 cm snail that hunts and eats pest snails while leaving fish, shrimp adults, and plants completely alone.
Will it live with a Assassin Snail?
We compare each fish against your assassin snail on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- African Dwarf Frog✅ CompatiblePeaceful · 4 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Amapá Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 24–27 °C (75–81 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Amapá Tetra in a shoal of 6+ or it gets stressed and nippy.
- Blackwing Hatchetfish✅ CompatiblePeaceful · 3.5 cm · Medium care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Blue Danio✅ CompatiblePeaceful · 4 cm · Easy care · 21–26 °C (70–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Cherry Shrimp✅ CompatiblePeaceful · 3 cm · Easy care · 18–28 °C (64–82 °F)
- Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Keep Cherry Shrimp in a shoal of 10+ or it gets stressed and nippy.
- Clown Killifish✅ CompatiblePeaceful · 3.5 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Clown Killifish in a shoal of 6+ or it gets stressed and nippy.
- Dawn Tetra✅ CompatiblePeaceful · 2.5 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Dawn Tetra in a shoal of 8+ or it gets stressed and nippy.
- Dwarf Spotted Rasbora✅ CompatiblePeaceful · 2.5 cm · Medium care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Dwarf Spotted Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Endler's Livebearer✅ CompatiblePeaceful · 3 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
- Keep Endler's Livebearer in a shoal of 6+ or it gets stressed and nippy.
- Eyespot Rasbora✅ CompatiblePeaceful · 3.5 cm · Medium care · 20–25 °C (68–77 °F)
- Compatible on the things that matter: shared water near 22–25 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Eyespot Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Glowlight Danio✅ CompatiblePeaceful · 3 cm · Easy care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Glowlight Danio in a shoal of 8+ or it gets stressed and nippy.
- Glowlight Rasbora✅ CompatiblePeaceful · 3.5 cm · Easy care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Glowlight Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Gold Ring Danio✅ CompatiblePeaceful · 3 cm · Easy care · 18–26 °C (64–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Gold Ring Danio in a shoal of 8+ or it gets stressed and nippy.
- Lambchop Rasbora✅ CompatiblePeaceful · 3 cm · Medium care · 23–28 °C (73–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Lambchop Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Malaysian Trumpet Snail✅ CompatiblePeaceful · 3 cm · Easy care · 21–27 °C (70–81 °F)
- Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Neon Tetra✅ CompatiblePeaceful · 3 cm · Easy care · 20–26 °C (68–79 °F)
- Both are peaceful, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
- Keep Neon Tetra in a shoal of 6+ or it gets stressed and nippy.
- Nerite Snail✅ CompatiblePeaceful · 2.5 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Northern Glowlight Danio✅ CompatiblePeaceful · 3.5 cm · Medium care · 18–24 °C (64–75 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Northern Glowlight Danio in a shoal of 8+ or it gets stressed and nippy.
- Pea Puffer✅ CompatibleSemi-aggressive · 2.5 cm · Medium care · 24–28 °C (75–82 °F)
- Peaceful + Semi-aggressive, but with no direct clash here; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Pygmy Corydoras✅ CompatiblePeaceful · 3.2 cm · Easy care · 22–26 °C (72–79 °F)
- Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Pygmy Corydoras in a shoal of 8+ or it gets stressed and nippy.
- Rainbow Emperor Tetra✅ CompatibleSemi-aggressive · 3.6 cm · Medium care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
- Tail-spot Corydoras✅ CompatiblePeaceful · 3 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
- Keep Tail-spot Corydoras in a shoal of 8+ or it gets stressed and nippy.
- Tailspotted Oto✅ CompatiblePeaceful · 3.5 cm · Medium care · 22–27 °C (72–81 °F)
- Both are peaceful, and their water overlaps around 22–26 °C — no size, zone or temperament conflicts.
- Both favour the bottom of the tank — offer enough cover so they aren't always in each other's space.
- Keep Tailspotted Oto in a shoal of 6+ or it gets stressed and nippy.
- Trinidad Guppy✅ CompatiblePeaceful · 3 cm · Easy care · 19–24 °C (66–75 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Black Darter Tetra⚠️ With cautionSemi-aggressive · 4 cm · Hard care · 21–28 °C (70–82 °F)
- Water hardness preferences differ (Assassin Snail 8–20 vs Black Darter Tetra 0–5 dGH).
- Black Ruby Barb⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Your 75 L tank is below the ~100 L this pairing really wants — crowding raises aggression.
- Keep Black Ruby Barb in a shoal of 6+ or it gets stressed and nippy.
- Cardinal Tetra⚠️ With cautionPeaceful · 4 cm · Medium care · 23–27 °C (73–81 °F)
- Water hardness preferences differ (Assassin Snail 8–20 vs Cardinal Tetra 1–6 dGH).
- Keep Cardinal Tetra in a shoal of 6+ or it gets stressed and nippy.
- Chocolate Gourami⚠️ With cautionPeaceful · 5 cm · Hard care · 25–30 °C (77–86 °F)
- Different pH ranges (6.5–7.5 vs 4–6); doable if you sit in the shared band, but not ideal long-term.
- Water hardness preferences differ (Assassin Snail 8–20 vs Chocolate Gourami 0–5 dGH).
- Keep Chocolate Gourami in a shoal of 6+ or it gets stressed and nippy.
- Crimson Red Betta⚠️ With cautionPeaceful · 3.5 cm · Hard care · 24–29 °C (75–84 °F)
- One likes softer water and the other harder (8–20 vs 0–5 dGH) — a compromise, not a perfect match.
- Crystal Red Shrimp⚠️ With cautionPeaceful · 2.5 cm · Hard care · 20–24 °C (68–75 °F)
- One likes softer water and the other harder (8–20 vs 2–5 dGH) — a compromise, not a perfect match.
- Keep Crystal Red Shrimp in a shoal of 10+ or it gets stressed and nippy.
- Dwarf Chain Loach⚠️ With cautionPeaceful · 6 cm · Medium care · 24–29 °C (75–84 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Dwarf Chain Loach in a shoal of 6+ or it gets stressed and nippy.
- Fire Red Licorice Gourami⚠️ With cautionPeaceful · 3.5 cm · Hard care · 23–28 °C (73–82 °F)
- One likes softer water and the other harder (8–20 vs 0–4 dGH) — a compromise, not a perfect match.
- Green Neon Tetra⚠️ With cautionPeaceful · 2.5 cm · Hard care · 24–28 °C (75–82 °F)
- Water hardness preferences differ (Assassin Snail 8–20 vs Green Neon Tetra 0–4 dGH).
- Keep Green Neon Tetra in a shoal of 8+ or it gets stressed and nippy.
- Humpbacked Tetra⚠️ With cautionSemi-aggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Humpbacked Tetra in a shoal of 8+ or it gets stressed and nippy.
- Morse Code Corydoras⚠️ With cautionPeaceful · 5 cm · Medium care · 23–26 °C (73–79 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Morse Code Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Neon Blue Rasbora⚠️ With cautionPeaceful · 2.5 cm · Medium care · 23–26 °C (73–79 °F)
- One likes softer water and the other harder (8–20 vs 1–6 dGH) — a compromise, not a perfect match.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Spotfin Betta⚠️ With cautionSemi-aggressive · 5 cm · Medium care · 23–28 °C (73–82 °F)
- One likes softer water and the other harder (8–20 vs 0–5 dGH) — a compromise, not a perfect match.
- Tiger Shrimp⚠️ With cautionPeaceful · 3 cm · Hard care · 20–25 °C (68–77 °F)
- Water hardness preferences differ (Assassin Snail 8–20 vs Tiger Shrimp 0–6 dGH).
- Keep Tiger Shrimp in a shoal of 6+ or it gets stressed and nippy.
- Tucano Tetra⚠️ With cautionPeaceful · 1.7 cm · Hard care · 23–28 °C (73–82 °F)
- Water hardness preferences differ (Assassin Snail 8–20 vs Tucano Tetra 1–5 dGH).
- Keep Tucano Tetra in a shoal of 10+ or it gets stressed and nippy.
- Wine Red Betta⚠️ With cautionAggressive · 5 cm · Medium care · 24–28 °C (75–82 °F)
- Water hardness preferences differ (Assassin Snail 8–20 vs Wine Red Betta 0–4 dGH).
- Discus⛔ Not recommendedPeaceful · 20 cm · Hard care · 28–31 °C (82–88 °F)
- Temperature needs don't overlap (Assassin Snail 22–26 °C vs Discus 28–31 °C).
- Your 75 L tank is below the ~200 L this pairing really wants — crowding raises aggression.
- Keep Discus in a shoal of 6+ or it gets stressed and nippy.
- German Blue Ram⛔ Not recommendedPeaceful · 6 cm · Hard care · 27–30 °C (81–86 °F)
- Temperature needs don't overlap (Assassin Snail 22–26 °C vs German Blue Ram 27–30 °C).
Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.
Assassin Snail care specs
- Care level
- Easy
- Breeding
- Hard
- Max size
- 3 cm (1.2 in)
- Min tank size
- 40 L (10.6 gal)
- Temperature
- 22–26 °C (72–79 °F)
- pH
- 6.5–7.5
- Hardness
- 8–20 dGH
- Lifespan
- 2–3 years
- Diet
- Carnivore
- Swim level
- Bottom
- Group size
- 2+ (shoaling)
- Family
- Nassariidae
- Origin
- Southeast Asia — Thailand, Malaysia, Sumatra (Indonesia)
What is an Assassin Snail?
The assassin snail (Clea helena, formerly classified as Anentome helena) is a small carnivorous freshwater snail native to Southeast Asia. It has earned a firm place in the aquarium hobby for one standout role: eating pest snails. Where bladder snails or ramshorns have overrun a tank, a handful of assassins will work through the population methodically over weeks. What makes them particularly appealing is that they accomplish this without bothering fish, adult shrimp, or aquatic plants.
Beyond their utility, assassin snails are genuinely attractive invertebrates. The shell is a tightly coiled, pointed cone — conical and elongated compared to the rounder ramshorn — dressed in alternating creamy-yellow and dark brown spiral bands. That high-contrast banding is the reason they are also called bumblebee snails. Adults reach up to 3 cm (about 1.2 in), a size that fits comfortably into nano tanks and community setups alike. Care requirements are modest: stable, moderately hard, near-neutral water and a substrate they can burrow into is most of the job.
Where do Assassin Snails come from?
Assassin snails are found across Southeast Asia — Thailand, Malaysia, and the Indonesian island of Sumatra are their core range. In the wild they live in slow-moving rivers, streams and lake edges, where the bottom is sandy or silty and water flow is gentle. Substrates there are loosely packed enough that snails can bury themselves partly or completely, which they do both to ambush prey and to rest.
Water conditions in their native habitat lean toward moderately hard and slightly alkaline to neutral — a direct reflection of the parameters they need in captivity. The soft, acidic water that suits many Southeast Asian fish will gradually erode an assassin snail’s shell, so that is one mismatch worth bearing in mind when planning a community tank.
What size tank does an Assassin Snail need?
The minimum recommended tank size is 40 litres (about 11 gallons). That volume provides enough surface area and stable water chemistry to keep a small group comfortable, and it is realistic given that assassin snails are almost always kept in pairs or small groups rather than singly. A group of two or more fits in 40 L; if you are running a larger pest-control operation or want a self-sustaining colony, a 60–80 L (16–21 gal) tank gives more room for both the assassins and their prey population to cycle naturally.
Substrate choice matters more than tank footprint. Assassin snails are bottom-dwellers that burrow regularly — they use the substrate to move, hunt and rest. A sand or fine gravel substrate 3–5 cm deep is ideal. Coarse gravel makes burrowing impossible and stresses the snails. Smooth pebbles, driftwood and dense low-growing plants round out a habitat that mimics their riverbed origin.
What water parameters do Assassin Snails need?
- Temperature: 22–26 °C (72–79 °F)
- pH: 6.5–7.5
- Hardness: 8–20 dGH
The hardness range is the parameter most specific to assassin snails compared to typical community fish. Moderately hard water (8 dGH and above) keeps the shell strong; consistent exposure to soft or acidic water causes pitting and thinning that shortens the snail’s life. If your tap water is naturally soft, a small amount of crushed coral or aragonite in the filter adds mineral content without spiking the pH.
As with any tank inhabitant, stability matters more than hitting precise numbers. A cycled tank with consistent weekly water changes of around 20–30% is more important than chasing perfect hardness on a test kit.
What do Assassin Snails eat?
Assassin snails are carnivores and natural predators of other snails. They track prey using chemoreception — sensing dissolved chemicals in the water — then extend a muscular foot, pin the target snail to the substrate, and feed through their proboscis. Bladder snails, Malaysian trumpet snails, ramshorns and pond snails are all taken readily.
In tanks where pest snails have been fully eliminated, assassins need supplementary food or they will eventually decline. Suitable alternatives include sinking carnivore wafers, frozen or freeze-dried bloodworms, small pieces of mussel or prawn, and any meaty sinking food. Feed sparingly: if they still have pest snails to hunt, supplementary food reduces their motivation to work. Uneaten food should be removed within a day to avoid fouling the water.
Are Assassin Snails aggressive — and what can live with them?
Assassin snails have a peaceful temperament toward anything they cannot overpower and eat slowly. Fish of all sizes are completely safe — assassins are far too slow to catch a healthy, mobile fish, and they have no interest in trying. Adult dwarf shrimp such as cherry shrimp and amano shrimp are also safe; they are fast and large enough to escape easily. The one genuine risk is to baby shrimp (shrimplets), which are tiny and slow enough that an assassin snail may consume them. If you are running a breeding shrimp colony alongside assassins, provide dense java moss, riccia or other fine-leafed plants as refuge.
The only animals that should genuinely not be kept with assassin snails are other snails you want to keep — nerite snails, mystery snails and rabbit snails will eventually be targeted. Assassins are methodical; they will eat any snail species they can subdue over time.
For a full breakdown of compatible and incompatible tank-mates, see Assassin Snail tank mates.
How do you tell male and female Assassin Snails apart?
Assassin snails offer no reliable external sexual dimorphism. Shell shape, size, colour and banding are essentially identical between sexes. Some keepers report that females are marginally larger at maturity, but the difference is too subtle and variable to be a practical guide at the point of purchase.
The practical implication is that you need to keep a group of at least two — and ideally four or more — to be confident of having both sexes present. Buying a pair is a gamble; buying four or six makes mixed-sex representation statistically likely. This is the primary reason the minimum group size is listed as 2, and why breeding difficulty is rated Hard: you cannot guarantee a breeding pair without trial and error or a larger group.
How do Assassin Snails breed?
Breeding in captivity is possible but slow and difficult to control, which is why it is rated Hard. When a male locates a receptive female, mating is prolonged — the male mounts the female and copulation can last several hours. After mating, the female deposits small, hard, translucent egg capsules individually onto hard surfaces: aquarium glass, plant stems, driftwood or smooth rocks. Each capsule contains one to five eggs.
Incubation takes around four to eight weeks depending on temperature, after which tiny juvenile snails emerge and immediately burrow into the substrate. Juveniles are small enough to be eaten by larger fish, and they grow slowly — reaching adult size takes six months or more. The overall output is low compared to pest snail species, which is exactly why an assassin snail colony tends to stabilise rather than explode into a new infestation. For most keepers, breeding happens incidentally rather than through a dedicated programme.
What are common Assassin Snail diseases?
Assassin snails are hardy invertebrates, but several conditions are worth knowing:
Shell erosion and pitting is the most common issue in captivity. Caused by chronically soft or acidic water, it appears as chalky patches, thinning at the spire tip, or irregular pitting on the surface. Prevention is straightforward: maintain hardness above 8 dGH and pH above 6.5, and supplement with crushed coral if your water is naturally soft.
Copper toxicity is the single greatest chemical risk to any invertebrate. Copper-based medications — widely used to treat ich and other fish diseases — are acutely lethal to snails even at low doses. If you treat a community tank with any copper-containing product, remove all invertebrates first. Check labels carefully; some all-in-one remedies contain copper.
Parasitic infections such as trematode flukes have been documented in wild Clea helena and can theoretically be introduced with wild-caught specimens or untreated live foods. Captive-bred stock from reputable suppliers carries far less risk.
Physical trauma from aggressive tank-mates — cichlids or larger pufferfish that crack shells — is a welfare concern rather than a disease, but worth noting. Keep assassin snails with peaceful community fish.
Health note: invertebrate disease diagnosis can be difficult. Confirm symptoms against a reputable aquarium-health or veterinary source before altering water chemistry or adding any medication, as many fish treatments are harmful to snails.
How long do Assassin Snails live?
Assassin snails live 2–3 years under good aquarium conditions. That lifespan is relatively short compared to larger snail species but typical for Clea helena. The main factors that cut a lifespan short are chronic soft or acidic water (shell erosion), copper exposure, and inadequate food supply leading to starvation once pest snails are gone.
Give them a stable, moderately hard, well-maintained tank, a source of meaty food, and a sandy substrate to burrow in, and most individuals will reach the upper end of that range. A small, self-sustaining group that breeds slowly will outlast any individual, making the colony effectively longer-lived than any single snail.
Frequently asked questions
Will assassin snails attack my shrimp or fish?
Adult dwarf shrimp (cherry, amano) and all fish are safe — assassin snails focus on other snails and cannot catch healthy, mobile tank-mates. Baby shrimp shrimplets are at some risk, since assassin snails will eat tiny, slow-moving invertebrates. If you keep a breeding shrimp colony, add dense moss and cover so shrimplets can hide.
How many assassin snails do I need to control a pest snail outbreak?
For a mild infestation in a 40–80 L tank, two to four assassins usually manage the population over several weeks. For a heavy outbreak, start with six and reduce feeding so they hunt more actively. They work slowly but persistently — expect the pest population to crash within one to two months rather than overnight.
What you need to keep a assassin snail
The baseline is a heated, filtered 40 L+ tank: a reliable heater to hold 22–26 °C (72–79 °F), a gentle filter that won't batter a assassin snail in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
As an Amazon Associate we earn from qualifying purchases — buying through these links costs you nothing extra.
