Pest snails in a shrimp tank: are they a problem, and how to control them
Almost every shrimp keeper meets them sooner or later: a few tiny snails on the glass a few weeks after adding plants, then dozens. The usual culprits are bladder snails, ramshorn snails and Malaysian trumpet snails. They are called pests because they multiply, not because they hurt shrimp. In most tanks the right response is less food and a little manual removal, not a chemical.
Which snail is it?
| Snail | How to recognize it | What sources say |
|---|---|---|
| Bladder snail (Physella acuta, also sold or seen as Physa) | Small, thin, glossy shell that coils to the left (opening on the left when the point faces up); fast-moving, often seen on the glass and at the surface | Up to about 16 mm tall; feeds on detritus and algae; hermaphroditic and able to self-fertilize; adults lay 50 to 100 eggs a week for up to a year; spread worldwide mostly through the aquarium trade, especially on plants (USGS) |
| Malaysian trumpet snail (Melanoides tuberculata, red-rim melania) | Long, cone-shaped shell; spends the day buried in the substrate and comes out at night | Average shell 20 to 27 mm; feeds on microalgae and detritus; can reproduce without mating and broods its young internally, which are born 1.2 to 2.2 mm long; imported by the aquarium trade since at least the 1930s (USGS) |
| Ramshorn snail (several species of planorbid snails) | Flat, coiled shell like a ram's horn; red, brown or blue color forms are common in the hobby | A common hitchhiker on plants, often kept on purpose; numbers rise with excess food (hobby reports) |
How they get in
USGS says the modern spread of the bladder snail is mostly through the aquarium trade, especially the movement of aquatic plants. Tiny snails and clear egg clutches are easy to miss on leaves, in moss and in the water shrimp are shipped in. Malaysian trumpet snails are usually buried in substrate or among plant roots. If you want to avoid them:
- Quarantine new plants in a separate container for a few weeks and watch for snails and eggs. See how to quarantine shrimp; the same idea works for plants.
- Buy tissue-culture plants (tissue culture plants), which are grown in sterile containers and arrive free of snails.
- Don't add the bag water when you buy shrimp; see how to drip acclimate shrimp.
Are pest snails bad for shrimp?
Usually not. Bladder, ramshorn and trumpet snails don't hunt shrimp, and they graze on the same algae, film and leftovers. Many shrimp keepers like them: they clean up uneaten food, and trumpet snails turn over the substrate as they burrow. The real downsides are cosmetic (snails all over the glass), competition for food in a tank that is already underfed, and the extra waste a very large population produces. The exception among common aquarium snails is the assassin snail, which hunts other snails and is sometimes reported to eat weak or newly molted shrimp; see cherry shrimp tank mates.
Why snail numbers suddenly boom
Snails breed as fast as food allows. A bladder snail can fertilize itself and, according to USGS, lay 50 to 100 eggs a week; trumpet snails need no mate at all. So a sudden boom almost always means more food than the tank's animals can eat: overfeeding, a big piece of food left to rot, or decaying plants. A few snails are normal. A carpet of them is a feeding signal; see what shrimp eat and how much.
Shrimp-safe ways to control pest snails
- Feed less. Feed only what the shrimp clear in a few hours, and pull leftovers. This is the step that actually shrinks the population; the rest just removes snails.
- Remove them by hand. Pick them off the glass, or net them in the evening when they are most active. Trumpet snails come up at night.
- Use a vegetable trap. Keepers commonly leave a blanched piece of zucchini, lettuce or cucumber in the tank overnight, then lift it out in the morning with the snails on it. Remove it within a day so it doesn't rot.
- Use a snail trap. Plastic snail traps baited with a little food work on the same principle.
- Vacuum the substrate lightly during water changes to cut down on rotting debris; see shrimp tank water changes.
Expect this to take a few weeks. Snail eggs keep hatching after you cut the food, so the numbers fall gradually.
Never use snail-killing treatments
Shrimp are invertebrates, just like snails, and many products sold to kill snails or algae contain copper. UF/IFAS notes copper is toxic to invertebrates such as snails, and the Merck Veterinary Manual says copper is extremely toxic to invertebrates and that they must be removed before water is treated with it. A treatment that wipes out the snails can wipe out the shrimp, and copper can stay in the tank afterward. See is copper toxic to shrimp before adding any medication, algaecide or snail product.
What about assassin snails and fish?
Assassin snails are a common hobby suggestion for controlling pest snails, but as noted above they are sometimes reported to eat weak or newly molted shrimp, so many shrimp keepers leave them out of a breeding tank. Snail-eating fish such as loaches and puffers will also eat shrimp. In a shrimp tank, feeding less and manual removal are the safer tools.
Don't release unwanted snails
Never dump aquarium snails, or plants and water that may carry them, into ponds, streams or drains. USGS documents both bladder snails and Malaysian trumpet snails as established outside their native ranges, with the aquarium trade as a source. It notes the red-rim melania can outcompete native snails and is a host for a parasite that affects fish, including an endangered darter. Give extras to another keeper or a store, or dispose of them humanely.
Track it
Write down feeding amounts and a rough snail count each week on the free Maintenance Schedule printable. When the count drops, you've found the right amount of food.
Frequently asked questions
Are bladder snails bad for shrimp?
No. They don't attack shrimp and eat the same algae, detritus and leftovers. A population boom is a sign of overfeeding, not a threat to the shrimp.
How did snails get into my shrimp tank?
Usually on live plants, as tiny snails or clear egg clutches. USGS says bladder snails mostly spread through the aquarium trade via aquatic plants.
How do I get rid of pest snails without hurting shrimp?
Feed less, remove snails by hand, and use a blanched vegetable or a snail trap overnight. Quarantine new plants or buy tissue-culture plants.
Can I use snail killer in a shrimp tank?
No. Many snail and algae treatments contain copper, which is extremely toxic to invertebrates, including shrimp.
Are Malaysian trumpet snails good in a shrimp tank?
They are harmless to shrimp and burrow through the substrate, eating detritus. Their numbers rise with excess food, like other pest snails.
Do assassin snails eat shrimp?
They hunt other snails and are sometimes reported to eat weak or newly molted shrimp, so many shrimp keepers avoid them.
Why are there so many snails in my shrimp tank?
Too much food. Snails breed as fast as food allows, and bladder snails can lay 50 to 100 eggs a week (USGS).
Sources: USGS Nonindigenous Aquatic Species, Physella acuta (acute bladder snail) species profile (up to 16 mm; feeds on detritus and algae; hermaphroditic, can self-fertilize; 50 to 100 eggs a week for up to a year; modern spread mostly through the aquarium trade via aquatic plants); USGS Nonindigenous Aquatic Species, Melanoides tuberculata (red-rim melania) species profile (also called Malaysian trumpet snail; average shell 20 to 27 mm; can reproduce parthenogenetically and broods young internally, born 1.2 to 2.2 mm; feeds on microalgae and detritus; imported by the aquarium industry as early as the 1930s; may outcompete native snails; host for a trematode that parasitizes fish including the endangered fountain darter); UF/IFAS, Use of Copper in Freshwater Aquaculture and Farm Ponds (FA008) (copper toxic to snails and other invertebrates); Merck Veterinary Manual, Management of Aquarium Fish (copper extremely toxic to invertebrates; remove them before treating); hobby references and recurring owner reports for ramshorn snails, traps and assassin snails; Shrimp Tank Hub's snails with shrimp and copper guides.