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FAQs on Snails in Freshwater Aquarium Assassin Snails, Clea spp.

Related Articles: Snails and Freshwater Aquariums by Bob Fenner, In vertebrates for Freshwater Aquariums by Neale Monks, Assassin Snails and Sulawesi Elephant Snails. Keeping Clea and Tylomelania in the Aquarium by Neale Monks, Fresh and Brackish Water Nerites by Neale Monks,

Related FAQs: Freshwater Snails 1, Freshwater Snails 2, & FAQs on: Freshwater Snail Identification, Freshwater Snail Behavior, Freshwater Snail Compatibility, Freshwater Snail Selection, Freshwater Snail Systems, Freshwater Snail Feeding, Freshwater Snail Disease, Freshwater Snail Reproduction, Snails by Species: Apple/Baseball Snails, Malaysian/Trumpet Snails, Ramshorn Snails,

snail issue; control. And plt ID      11/20/13
Hi Neale, hope you are well.  My tanks are doing well, so I haven't needed advice lately.
<Well done!>
Here is a photo of a plant I'd asked about before.  Someone told me it's probably called naja grass.  What do you think, have you ever seen it?
<Certainly looks like Najas guadalupensis
. But no, I've not seen or kept it. Seems to be rarely traded here.>
It has long stringy roots but doesn't succeed in being planted for me at least in the lower light setting.
<Correct. It looks much like other aquarium "tangle weeds" such as Ceratophyllum demersum and Elodea spp. Basically, it wants to be left loose, floating under bright light, and it will send down white roots to form loose anchors onto the sediment. It'll grow from the waterline downwards rather than from the substrate upwards.>
It tends to have explosive growth like the java ferns if it is growing tangled among other floating plants.
The one I'm referring to in this picture is in the center and not the annubias or the water wisteria/water sprite(i have both or one of those). 
It's lacy and the roots are floating too.
Here is my real question though:
In your experience, do assasin snails ever get each other ever? 
<Possibly, but this seems rare.>
I originally had 5.  Some time back I found one smaller empty shell.
Lately I had only ever been aware of 3, though it's possible one is hiding.
 But today I noticed another empty shell, this was one of the larger ones.... It's been there unmoved upside down since yesterday. I had hoped these critters would eventually breed and not cannibalize.  I have heard stories that they do reproduce, but I have seen no evidence of this.
<Ah, they do breed. But they're also unusual in not being hermaphrodites.
So if you (unluckily) got few/no females, then your population would die out.>
Would they ever react badly to a water change, are they sensitive or hardy?
<They seem fairly hardy.>
It's heavily planted.  This time I cleaned it a little more thoroughly in the vacuuming, I changed a little more water than typically (45% maybe as opposed to 25-30%, and my tank has a larger than needed filter for currents), but there's also lots of decor and plants and a well established filter, and the snails were removed and kept in their water during the cleaning.  The fish have shown no signs of stress.  They even gave birth since the cleaning.  The endless lime green endlers....
Do the assasin snails eat baby cherry shrimp?
<Some reports suggest they can, but it probably depends on many factors including whether the baby shrimp had places the snails couldn't go, like behind/inside filters, and how many of each you started off with.>
That tank could use some resident snail cleanup, but I would hate to stick one in there and have him feasting on shrimp instead.  I'm wondering if there's anything that could coexist with them and do snail patrol that wouldn't eat them too.... Probably not.
<I wouldn't keep Assassin Snails with my *only* group of Cherry Shrimps, but I have combined them in one aquarium while keeping another population of Cherry Shrimps going without Assassin Snails in another tank.>
The funny thing...I have never seen one eating a snail, even with baby snails in the near vacinity.  One in particular has been very active since the clean.  I wonder if he was the culptet in the other's demise....
<Oh, Assassin Snails can/do eat snails, but they're scavengers more than anything else, so if there is other food, they'll eat that as
Thank you,
<Most welcome, Neale.>

Re: snail issue     11/20/13
Thank you.
I'll try buying a few more assasins then.  Maybe I just didn't get both sexes.  They're good cleaners and an attractive addition to the tank as well.
<Sounds like a good plan. Cheers, Neale.>

Assassin Snails   4/25/12
Good day,
Not sure if it's the right email that I'm sending this to.
<Sure is.>
Just a quick note on your page about these snails. I bought 3 yesterday to get rid of my other snail infestation. Have some cherry and amano shrimps in the same tank.
When I got to the tank this morning, I found a red cherry sucked almost dry with one of the assassins still busy cleaning it out.
<Can happen
. My specimens seemed to ignore the shrimps, and the Cherry Shrimps bred merrily away with the Assassin Snails. But the Assassin Snails are hunters, and they surely can take down a sick/weak shrimp given half a chance. They will also eat the moults -- don't forget shrimps cast off a moulted exoskeleton each time they grow. For the snails, moults are a good source of calcium. What you have there could very easily be nothing more than harmless recycling of a shrimp moult into snail shell!>
I don't mind the loss since I've learned something from it.
Have a great day.
<You too, Neale.>

Assassin Snails for Snail Control in Soft Water 1/28/12
Hello again!
I made a mistake last week. With my last plant shipment I absent-mindedly added the plants to the tank without a thorough snail inspection. By the time I realized it was too late and, of course, this shipment must have had a few snail eggs. I have removed three snails from the tank already and see snail eggs littered across the glass. My lfs has assassin snails which I want to use, but my GH is 125 and KH 71 ppm and I know this is soft for snails. My tank already has a school of Danios and I will be adding a school of cherry barbs after they finish quarantine next week (although I can hold off on this) so I wasn't sure about adding shells or something similar to increase the GH. I don't necessarily want/need to keep the snails and was wondering how they will do temporarily. I can easily remove them and put them in a small hard-water tank after they finish off the other snails but, as I have never done this before, I don't know how long this will take. I considered adding Gouramis as I saw these will bug snails, but as my tank is a 20 tall and I already have two schools of 6 fish each this doesn't seem like a viable option (unless I decide to permanently keep the barbs in the 10 gallon). I have a couple shrimp in the 20 tall so I can't use a molluscicide but will definitely use it for any new plants in the future. I assume if I rinse new plants in this and then rinse them in plain water I will not need to worry about the chemicals leaking into my main tank? Any advice would be helpful!
Thank you!
<If the water is soft, the other snails should breed only slowly, if at all, so removal by hand would be the ideal here. If you must use Assassin Snails, provide a small piece of cuttlebone for them to consume. You can't stop snail shells dissolving ("pitting") in soft water, but you can at least make it easier for the snails to grow their shells in the first place. Even so, these snails will probably do poorly in acidic water in the long term, and may have a rather short lifespan. Cheers, Neale.>

Clea helena question, + observations 9/7/11
First, my thanks. I'm a card-carrying newbie, but many a disaster was avoided and even more were mitigated with the excellent advice that you folks share. It's not all fire-fighting; following your stocking and compatibility recommendations, even belatedly, has given me three happy little tanks. Unless something big and heavy gets in the way, you and my great LFS have spawned another "lifer".
Second, a Clea helena question: Nearly half of my juvenile assassins have a pinkish-rusty stripe instead of the yellow stripe. I don't know if they outgrow it or not, since observed it only last week. Water quality is maintained at NH3 and NO2 = 0, NO3 <15, pH 7.5, basic-to-acidic, heavily planted tank; plenty of cuttlebone for nibbling; so I haven't worried...yet...just curious. Diet? (Their favorite "snello" treat includes ground cichlid pellets. Possibly snacking on dwarf shrimp mates.)
Genetics? Any cause for worry or caution, that you can think of?
Third, Clea helena observations: Neale M.'s words sold me on these little rascals, and I've had not a moment's disappointment. May I add a little to your data, though?
I introduced 3 adult assassins to a 6-gallon, underwater jungle stocked with 4-5 doz RCS (do dwarf shrimp populations -ever- become self-limiting?)
on 1 Apr 2011. Plenty of red Ramshorns and MTS were available for munching, in addition to goodies the RCS passed over. By June 3, I'd moved 8 tiny assassins to another tank. On July 5, I moved 6 juveniles to a third tank.
Over the last two days, I removed 40+ juveniles and donated them to aforementioned LFS, plus moved another 8-10 juveniles to the other two tanks. I suppose their warm water (78F-80F) may be causing the grown-ups to burn their snailio candles at both ends, since reproduction hasn't been that, um, "overwhelming" in the cooler (74F-76F and 73F-75F) tanks.
Nevertheless, Agamemnon and Clytemnestra have been renamed Trudie and Sting. Paris is pretty much true to his, or her, namesake (pick one).
Regarding diet, these over-indulged critters have never, as far as evidence indicates, touched my MTS or Physa. They will topple everything and spit out flakes in order to get to a Ramshorn, though, assuming they beat their Betta tankmate to it. They and/or Betta-buddy also demolished 50 or so RCS within 2 months. Most fascinating, however, was observing 4 juveniles in 2 sizes take down a healthy Tylomelania while he was munching his zucchini treat. Two days later, I watched 3 juveniles kill one of my 2 Nerites (hey, everybody's got to eat). And so, while all were lying around burping like kings-of-the-jungle after the feast, I cleaned house, except for adults and lurkers, and into the LFS baggie or other tanks they went. Come to think of it, they have no business, or perhaps too much, in the dwarf Cray/crystal red shrimp tank!
Because it bears repeating, thanks for EVERYTHING you do, and for the hours you've dedicated to it.
<Harriet, thanks for your informative e-mail. This is all very interesting.
Yes, juveniles have slightly different, somewhat pinkish colouration. Your specimens seem to breeding rather quickly, but you are keeping your tank warmer than me (I rarely keep tanks above 25 C/77 F because so few fish appreciate such warm conditions). While I have seen adults consume juvenile Tylomelania, they haven't taken down any of the adults (which in my case are about 2-3 inches long) and they've never shown the least interest in my Nerite snails. But perhaps my specimens aren't typical. All extra information is much appreciated, so thank you! Cheers, Neale.>
Re: Clea helena question, + observations 9/7/11

Thank you, Neale. I'm quite relieved to hear that the pink-to-rust color is natural, and -not- indicative of mutant spawn bent on world domination; or, worse, my fault in gross overfeeding.
<If it is a problem, I'm making the same mistake! But they seem to grow up the regular colours.>
Regarding juvenile hunters, there was no time to photograph the event, since there was only an instant (in snail time) between "munching with..." and "munching on'¦."
<Always the problem with predators is telling when they're hunting and when they're scavenging. They are certainly scavengers that will eat sick, dying or dead snails as well as most anything else, including dead fish.>
As the first two assassins, scarcely 1/2-inch shell length, wedged themselves between the snail (Tylomelania zemis? sold in US as "chocolate poso") and its shell (smaller than your tylos, about 1-3/4 inches), it jumped--an exaggerated flinch--then slowly relaxed. During that time, the "baby", 1/4+-inch, assassins were climbing the poso's head, one from the sand in front, one dropping down from the upper shell. Considering my lack of knowledge and experience, it's hard to tell at that scale if they're contributing or watching.
<Quite so.>
In another 60 seconds or so, other assassins were scampering toward the feast. So maybe adulthood, but not full growth, is reached by the time the anentome approaches 1/2-inch?
<Sounds about right.>
The trio who appeared to bag the Nerite were all more than 1/4-inch shell length, but not yet 1/2 inch. Again, everyone was busy tidying up a squash skin, when the three assassins ducked under the Nerite. The big snail wobbled a bit, but I thought perhaps it was from being lifted by little guys that are essentially moving pebbles. The assassins disappeared underneath, and I might have assumed they dug into the sand had they not been joined minutes later by a crowd of onlookers, all sizes, hell bent on a meal. The lot managed to tilt the Nerite shell. At that point, I had other things to do. Calling my LFS to arrange for multiple adoptions and a couple of new big snails, to start with.
<Very curious. It's not clear to me how they hunt in the first place, so possibly they use poison or something else to paralyze their prey.>
Considering the level of activity, I have moved/am moving remaining assassins out of the Betta tank to a cooler one with no intended, live targets other than MTS and Physa. That tank is heavily planted, also with a cable heater in the dirt, so there could be already a city of them under there with empty MTS shells stacked in the corners, for all I know. However, the plan is to move them out of the fast lane and warmth of the city lights into something a little more snail-paced.
<Sounds great.>
Thanks again for your various stocking recommendations. As a beginner, I've found them easy to care for, and first-rate "edu-tainment"!
<They are certainly very fun snails to keep, as are the Tylomelania, and bring a bit of the "reef tank" quality to our freshwater systems. It's so easy to watch snails and shrimps doing their thing, you sometimes forget it's a freshwater aquarium! Cheers, Neale.>

Assassin Snail Behavior -- 05/07/11
Dear Crew,
I purchased a Clea helena more than six months ago and reported to Neale that after at least six months I found a tiny baby. The strangest thing has happened. I hadn't seen mom in several weeks but I got up one day to find the entire infestation of rams horn snails dead. I mean going from at least 50 to 0. I was concerned about water quality then noticed that there were plenty of rams shells with no one home. I thought the baby must have finally gotten his "teeth".
The weird part that got me testing the water is that all the rams from the floating plastic plants were also gone and I couldn't understand why they would come down from the floating sanctuary. Then the leaves on the plastic plants turned a dark purple I assume algae that is no longer being eaten.
Today I added a couple algae wafers to the tank for the Cory cats to snack on and guess what? I bet you can guess. I spot THREE assassin snails and to my utter surprise the smallest one is hanging on to the floating plant hopefully cleaning it up.
I don't think there's any special concern but I wanted to check because the food population (of live snails at least) has dwindled. Now I kind of miss the little nuisance snails that were kept at bay when there was one snail but are totally gone with three. I assume there might be some eggs for the rams and maybe there will be a new generation but it's been at least three weeks. The assassins killed every single one regardless of size.
One of my Zebra Nerite passed away a few months ago and I guess three Clea Helena probably equal one of those or not even mass wise. I also have a feeling that three might not be the max I see over time.
Still, Clea Helena is pleasant to observe which is rare but I know at least today that the algae wafer got them to show themselves as a group.
The question is, should I be varying the tank feeding to compensate for the lack of live treats? I'm assuming they will do OK cleaning up left over flake and algae and obviously the wafers were appreciated.
Any feedback appreciated. I'm pretty sure all is well but I like to check in when there's a major change.
thanks, Greg.
<Hello Greg. Ramshorn snails may well be eaten in significant quantities by Clea helena. But Nerite snails of larger size than the Clea helena do not seem to be at substantial risk. Possibly the odd one might get eaten, but do remember Nerite snails don't always adapt 100% to aquaria. As a ball-park estimate, it seems that out of every three or four Nerites you buy, one fails within the first few weeks, while the others go on to live for years. That's been my experience anyway. I have Nerites and Clea helena in the same tank, and there have been no Nerite deaths in 3 years. Clea helena do seem to specifically target small snails, ideally ones less than their own size. They are scavengers too, so if a snail dies from some other reason, they'll eat that. You don't need to specifically feed them anything. Their population will adjust to the amount of food available. In an aquarium many of the Clea helena will be going for flake food, bits of algae wafer, bloodworms, krill and so on, as well as the normal fauna of worms and crustaceans in your aquarium. You don't particularly want to increase your Clea helena population -- what you want is to build up your original adults into a stable population that minimises the impact of pest snails. If you want to add some snails, try Tylomelania snails. Clea helena will exterminate their babies without problems, but the adults, which are up to 12 cm/5 inches long, are far too large to be at risk. These snails are excellent scavengers and I've found them particularly good alongside catfish, predatory characins and so on. Despite initial reports to the contrary, Tylomelania appear to be extremely easy to maintain and are now fairly widely sold under a variety of names -- Yellow Rabbit Snails, Elephant Snails, Helmet Snails etc. Cheers, Neale.>
Re: Assassin Snail Behavior 5/16/11

Thanks Neale. I wish I would have been faster on the camcorder because one of the "2nd generation" Clea helena appeared to go after one of the Nerites last night. It was quite exciting for about 5 minutes. When on the sand the assassin seemed to be trying to scoop his horn under the belly of the Nerite. Have no idea if the Nerite actually sensed danger or not but to get away he went onto the glass side. The assassin gave up after about a minute following on the glass. Doesn't seem to be in real danger. First time I saw any such thing and I guess with the armor there isn't much to worry about.
Who knows what damaged could have been caused if any as long as the Nerite keeps moving. The Nerite is several times bigger than the assassin.
<Yes, I think after a while the Clea end up ignoring the much larger Nerites. But "your own mileage may vary" as they say. Nerites are pretty cheap here, so even if I'm wrong, there's not much lost.>
I found "mother" Clea helena today for the first time in weeks. She seems fine staying buried most the time. When it was just her the Ramshorns were held at bay at maybe 50 or so tops at hatching season but now they are completely gone. I counted FOUR assassins today. It appears to be three different generations based on size.
<Agreed, this is what I tend to see. Clea helena is a slow breeding species, but under good conditions does breed steadily.>
I don't know that much about their reproduction but it seems "mom" came in with a fertilized egg and now these two have mated to create two more specimens. I understand they are slower than the Ramshorns but they seem to be going about it pretty quick at this point but of course have killed off the meaty part of the food chain.
<At some point food will becoming limiting, and because they're carnivores rather than herbivores, the upper limit on population size is likely to be less per gallon than, say, Ramshorn snails.>
I want to make it clear that this increase in Clea helena population wasn't intentional. I brought home 1 specimen and now I have 4. The first one entered the tank in early November 2010 and the second one was spotted in March of this year. I wonder now if the two newest that I've spotted (and by far the smallest about the same size) were not a breed from between first and second generation and were left over from the original eggs that may have come home with mom. It seems four months for the first baby to be seen and two more for the second two. Two months seems rather fast and spells trouble unless I get into the breeding business but like you said the environment should sort it out.
<It will, or you can always remover surplus snails and sell them. There's a good market for Clea helena.>
With regards to what you said about adding Tylomelania, I assume you mean if I'm interested in another snail species and not to add them as a food source. Honest, I'd be happy with just the Nerites and I only added one assassin to keep the Ramshorns at bay. I didn't want to kill them all off because I was worried about what to feed the assassin afterwards. Now I have four instead of one but no Ramshorns. I assume though your advice overall is not to sweat it.
<Quite so. In all my tanks they seem to level off at a population where I'll see a couple or three if I hunt about, but no more than that.>
The only other odd side effect is that certain species seem to stake out their favorite areas. With the Ramshorns gone an area of black sand now has a green tint to it, I assume because the Ramshorns aren't there to till the soil. The catfish don't seem interested in that section of the tank for some reason and the sand just isn't churned as often.
<Curious. The Clea helena at least are excellent bioturbators.>
PS: My Trichogaster leeri male is doing the sand thing again. This time he's actually building his first bubble nest. I am supposing last year when the females were about half his size that either he wasn't old enough to understand his dad duties or the females weren't ripe enough. He is SUPER ORANGE now. Much brighter than last year.
The sand thing is interesting and I haven't seen it documented anywhere else. He scoops sand up from the bottom and dumps it on whatever is under the bubble nest. That used to be a cave which confounded me for days since I knew the filter wasn't doing it. Now there's 10" tall plastic tries that he's coating with sand.
<It is odd behaviour. Normally, these fish cement bits of floating plant debris into their nests.>
Life both out of and inside the tank are fascinating.
<Sounds to be the case! Cheers, Neale.>

Assassin snail eggs? 4/4/2011
I have a twenty gallon tank with a single female Betta, 3 assassin snails, and I just added 6 glass or ghost catfish.
Two of the assassin snails were crawling all over each other for almost a half a day and the next day I found about 10 little spots on the glass that look like sacs with something inside. They're about 1mm.
I've included a pic but I'm sure if you can tell from it.
My question is can I use a gravel cleaner in there or will I take a chance on killing some of them? How long will I have to wait?
Thank you,
<Hello Tim. Clea helena lay eggs in transparent, sachet-like capsules about 1 mm across. They tend to be dotted about on hard surfaces, far apart rather than in clumps. Once they hatch, the baby snails dive into the substrate, so yes, you want to leave the substrate alone. I've only kept them in tanks with sand -- in the wild they burrow into sand and silt -- and the juvenile snails reappear at shell lengths around 5-6 mm long,
usually several months later. I wouldn't keep them in a tank with gravel given their ecology. In any event, using a gravel cleaner is generally pointless so I'd lay off if you want to breed these snails. In a sandy tank you don't ever use a gravel vacuum, the snails cleaning the sand all by themselves. Cheers, Neale.>

Re: Assassin snail eggs? 4/4/2011
The substrate is mostly the smaller material for growing plants. I wasn't planning on breeding them but it happened. Should I try and make a sandy area for them?
<Wouldn't bother for now. See what happens!>
<Do have some personal observations here:
Cheers, Neale.>

Clea helena New Baby 3/15/11
I know I don't have a perfect track record of identifying new born snail species (I brought home pests on plants and had no idea back then) but I'm sure I'm right on this one. I have a new baby Clea Helena.
<Cool! They breed rather slowly, but yes, they do breed.>
Thing is, I only had one since November 1st. I haven't seen "mom" for a bit but that isn't unusual.
<Indeed not.>
There's plenty of empty Ramshorn shells that shows the job is being taken care of. This new snail though is extremely tiny.
<Yes; a couple of mm long, with a small brown shell, sometimes with the yellow stripes visible.>
So even though I haven't seen both together, there's no way it's the same snail. I'm talking about the size of a baby Ramshorn. I would never have seen it if it wasn't on the glass and it is so small I'm surprised it wasn't eaten.
<Somehow they survive!>
I'll get a picture later after the camera charges. I just didn't know how unusual this is to start with "one" and four months later have two. I know this is a rather new to the trade creature so I wanted to share my discovery.
<Thanks for sharing. Mine do breed, and to a degree, you should end up with a stable population. Better still, they help to keep pest snails in check.
Cheers, Neale.>
Clea helena New Baby
<PS. I have a photo of a young Clea helena about halfway down this page:
Cheers, Neale.>

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