assassin snail (Clea helena)

Not a good algae eater, but a great choice for keeping those small pesky snail populations down and not eating all the plants in sight. And they don’t multiply like those pesky small snails.  Adult size up to 2.5cm, minimum tank size 40 litres, will eat 1-2 snails per day. Good for beginner aquarists.

The assassin snail (Clea helena) is a freshwater snail that is highly sought after in the aquarium trade for their ability to prey on pest snails. They are found throughout much of Southeast Asia, and are native to Thailand, Malaysia, and Indonesia. Like most aquarium snails, this species is fairly small. A healthy adult will reach around 2.5 cm, but they can grow larger depending on their diet. Wild assassin snails tend to be a little bigger than those bred in captivity.

Shells come in lots of different shapes and size and it’s the shell which helps when identifying the species. An assassin’s shell is conical with brown and yellow stripes running around it. This has led some people to nickname it the bumblebee snail. Sometimes they might lack stripes and be completely brown in color; but it’s rare. An interesting part of the shell is called the operculum. This acts like a trapdoor to shut off the shell when the snail is hiding inside. Inside the shell is a strong, muscular “foot”. The muscles it contains are contracted to move the snail forwards, at a very slow pace. The head has a pair of short tentacles attached. These are very sensitive and help when moving around the tank and looking for food. A pair of eyes can be found at the end of a long pair of tentacles; these can detect light and motion.

Behaviour

Assassin snails are famously slow, so they won’t introduce much activity to your tank.  You’ll see them less during the day, as they choose to come out at night to feed. They’ll break this habit if they sense that you’re feeding them in the daytime. They’ll emerge and head straight to the food. A lot of their time will be spent buried in the substrate. They wait here for anything that moves above them (like smaller snails). They’re not an aggressive species and won’t bother your fish, but any slow-moving animals that are small enough to be eaten might be seen as prey.

As long as you’re not overstocking the tank you can keep as many or as few as you want.

Tank Conditions

Starting from the bottom of the tank, a sandy substrate is important since that’s where they will spend most of their time. The substrate needs to be small and soft so it doesn’t damage their sensitive tentacles.

Assassins aren’t fussed about plants because they don’t need them as food or shelter.  So this makes them ideal for planted tanks or paludariums. If you keep lots of plants and want some snails, most other snails would start to eat the plants damaging them. Assassin snails will leave them alone, so your plants can flourish.

Whether you add decorations is up to you, but adding a couple gives your snails space to climb, and places to attach eggs when breeding.

The water needs to be well filtered and heated. If conditions change then your snail’s health will rapidly deteriorate, so keep everything consistent.

Your filter outlet will create enough of a current for them, fast-flowing water isn’t important. Lighting isn’t a problem either; they will thrive with any lights.

Compatibility

Assassin snails will pay little attention to any fish in the tank, so feel free to add anything you like.  However, the problem is there are lots of fish that might try to eat your snails.  Most common community fish that are small and swim in the mid-levels of the tank will be fine: cherry barbs, celestial danios, guppies and neon tetras are some good examples. Some bigger options are peaceful gourami (like dwarfs or pearls), rainbowfish or angelfish.  Bottom-dwelling fish can be more dangerous as they’ll come across your assassin snails much more often so stick with peaceful scavengers like Corydoras catfish or Otocinclus catfish.

Though assassins will eat other snails, it’s usually only the small pest species. So you can add the larger (same size or bigger) varieties of snails such as nerite or mystery snails.

Feeding

Assassin snails are a carnivorous species, so their diet doesn’t include any vegetation. They’ll ignore any plants or algae in the tank.  They will eat other smaller snails, so they are often used for pest control. Trumpet and Ramshorn snails are a couple of the most popular snacks. Soft snail eggs and shrimp fry might be of interest too.  Assassins don’t usually eat their own young or eggs though.

Blood worms are also a favorite. They’d eat a lot of worms in the wild so this is a good way to vary their diet while sticking to their natural prey. Brine shrimp are another live food you can use.  They may eat some flake and pellet foods, but this varies by individual. Algae wafers might also be eaten because of their high protein content.

The choices you make with their diet will influence how they grow.  It’s hard to know how much to feed them since they eat at their own pace, 1-2 snails a day will be enough. If you’re keeping them with fish, then they’ll scavenge any uneaten fish foods too.

Care

If you’re looking after snails for the first time then you need to realize that assassin snails can get diseases just like fish can.  Their shells can be affected by a number of issues. You might start to see white spots appearing across their shell. These are probably parasites that have latched on to the outside. There are lots of different parasites that use snails as part of their life cycle.

It’s not always easy to keep their shells strong and healthy. If they weaken then they could crack and break; this would most likely be fatal.  Calcium is important for maintaining a hard shell. They should get this from their diet, but you can add calcium supplements into the water if they’re not getting enough.

The shell’s growth can be stunted if temperatures are too low or if they aren’t eating enough.

One element to keep away from your tank is copper. This is toxic for most invertebrates. Check the contents of anything you add to the water, medications often contain some degree of copper.

Assassins are particularly susceptible to poor water quality; they need consistently clean water to stay healthy. Perform regular water changes (every 1-2 weeks) to keep the nitrate levels to as low as possible.

See Fish Disease Diagnosis and Treatment at Rebel Pets for help with diagnosing and treating diseases.