One of the common questions seen on the boards is how to control snails that are “taking over a tank”. These are sometimes assumed to be the result of some sort of spontaneous generation, who came in by magic and devour everything in the tank, including killing prize specimen fish and perhaps coming out at night and raiding the pantry, or at least the dog bowl.
Well, the reality is slightly different. Snails come from parent snails, most commonly by eggs deposited on solid surfaces, but some few are livebearing, producing miniature adults released directly by the parent. Snails are mainly vegetarian, but not at all exclusively so. They are more than willing opportunistic meat-eaters, not true carnivores, but at least omnivores. They have a rasping tongue-like structure (the radula) used to scrape whatever surface they find themselves crossing which has a “tasty” surface coat, be it green algae, diatoms (brown algae), a dying plant leaf, or an uneaten food flake, food pellet, or dead fish. Some burrow in the tank substrate and come out to feed most when the tank is dark, but most types in tanks are always visible.
Snails are gastropod mollusks, meaning they fit into the phylum Mollusca, in the class Gastropoda. Mollusks are as a rule soft-bodied creatures (lacking internal supporting structures such as bones), mostly protected by some type of external shell (snails, clams, oysters). The gastropods have a single shell, mostly coiled. The shell is composed largely of calcium carbonates. For tank-keepers, that last means that they prefer harder more alkaline waters (which tend to have higher calcium and carbonate content). Some snail’s shells will degenerate (by partially dissolving) if they are moved to soft acid waters. As this is their primary defense against predators, it means that even weak-jawed fish can get to the tasty snacks offered by their soft bodies.
Malaysian trumpet snails
Popular urban myth: Snails can take over a tank, multiplying endlessly until the tank is a one seething carpet of snails. (I do admit that is a pretty off-putting image, a bit Indiana Jones-ish). Fact: populations of common tank snails (common pond, common ramshorn, and Malaysian Trumpet Snails or MTS) are entirely controlled by the food supply. If your tank water is low in nutrients (especially nitrate and phosphate), algae growth will be limited. As algae are the snail’s primary natural food source, the numbers of snails will be minimized. If the fish are overfed, three food sources are offered: First, the excess uneaten food itself (of whatever type – flake, pellet, or frozen). Second, the excess fish poop, which from overfed fish, will consist in significant part of undigested food (fish have little or no natural suppression of appetite in the face of plenty, they keep ingesting even though undigested food is being dumped out the back end of the GI tract). And third, the additional nutrients released to the water by bacterial/fungal action on even the fully digested fish and snail poop, which in turn will feed algae. So as the tank-keeper, your maintenance practices will influence the snail population strongly. Overfeed and/or overstock, and you promote snail population explosions. Stock conservatively and feed judiciously, and you minimize snail populations to minimal maintenance levels. Ditto for water changes and tank vacuuming. Conscientious vacuuming will remove uneaten or only partially digested food/poop before it affects the water adversely. The same frequent cleaning of mechanical filters will also reduce the quantities of nutrients released into the water column from captured organic debris. The water changes will dilute out metabolite and other nutrient build-up. Just cleaning the tank glasses of algae on a regular basis will assist in snail population control.
Popular urban myth: Snails will attack and devour fish. Fact: No live healthy fish will submit to being grated on by a snail rasping away at its flesh. A quick flick of the fish’s body and the snail is elsewhere, and so is the fish. A dead fish obviously can neither notice nor react, and so is fair game and a nutritious meal. A comatose/dying fish could well be beyond reaction, and could even be argued that this was the immediate cause of death. IMHO (In My Humble Opinion), a fish in that state is effectively dead if it is so far-gone that it cannot and does not react to a snail or to human or net touch. The other fish in the tank will take part in the same meal- and do so much sooner and more effectively than the snails. That last is not at all good tank practice. Some of the worst biological hazards in tanks are transmitted well by such postmortem consumption by tank mates, including tuberculosis and Neon Tetra Disease, plus several intestinal parasites. If a fish is so bad that it cannot swim or react to touching, it should be out of the tank, either euthanized or at least isolated in peace.
Urban myth: Snails just appear. Fact: Spontaneous generation is out. As stated in the introduction above, snails come from snails. Their introduction to the tank may not have been noticed, but it happened. Many introductions to tanks are done on plants. Common pond and common ramshorn snails lay eggs in transparent gelatinous globs attached firmly to solid objects. Plants are a prime site- if this is where you feed, there may well be immediately available food for your babies when they emerge, so it is a good place to put your egg mass. I am confident that a snail does not really think such thoughts, but placement instincts provide the right locations. Tank glass, rocks, pots, filter tubes, etc may also be used, so that any material transferred from one tank to another may carry snail eggs if not examined carefully and/or disinfected. This includes gravel and filter media. Disinfection by various commercially available remedies may knock off baby to adult hitchhikers, but are IME (In My Experience) less certain with the eggs. Baby snails, which may be tiny and dot-like, may even be introduced with fish- if the fish was net caught against the glass of the LFS tank, or among plants, and then fish, water, and hitchhikers are all released into the tank at home.
Dangerous urban myth: Commercial snail killers are safe for tanks, fish, and plants. Fact: These remedies have been shown time and again to be dangerous to both fish and plants. The effects may vary from death to infertility for the fish; the effects tend to be lingering decline for the plants, but sometimes these treatments cause sudden collapse. Many of these “treatments” are based on copper or other toxic metal, or antimetabolites that may affect snails more quickly than fish or plants, but are far from “safe” for extended exposure. In a word, don’t use these if you value your tank and its inhabitants. They are not 100% effective either. Should they kill the excess population of snails (they are not necessarily ineffective), you are then faced with the chore of getting the mass of dead snails out of your tank before the tank is polluted (snails decompose with astonishing speed) and the filters may be overloaded. MTS snails can close their operculum and wait out such treatment, to reappear in good health when the water is better. Manual, non-chemical, techniques are far safer.
The simplest excess snail population short-term control is by feeding them. Not the contradiction it seems to be, the feeding is by use of food in such a way that the feeding snails are removed with a container, or with the leftover food. Select a fairly heavy lettuce leaf, run hot tap water over it to wilt it a bit, or just leave it on the counter to wilt an hour or so, then clip or weight it down in the tank, preferably just before lights-out. The next morning, collect the leaf and the attached snails. Drop in a plastic bag and put in the freezer for the day. That night discard the bag, leaf and dead snails. Repeat as needed for control while you are cutting back of excess food, fish population, and upgrading vacuuming, filter upkeep, and water change routines. An alternate technique would be to use an algae wafer or food pellet, sunk to the bottom of the tank in a bottle whose neck is too small for the fish, but allowing entry of the snails. Next morning, remove the bottle with contained snails, rinse them into a styrofoam or plastic disposable cup or bag, freeze, and discard as before, repeating as needed for control while taking the measures required to correct the underlying cause of the problem rather than just reducing the symptoms.
Also note that the snails have been living on something- algae, fishfood, whatever. That something or various somethings are still going to occur in the tank unless tank maintenance practices are modified, and you may be faced with algae outbreaks, fungus on or in the gravel, or bacterial or algal water cloudiness. IME, snail poop is easier for the tank to “handle” than the things that result in snail poop. Remember that you must always treat or correct the underlying cause of problems; not just relieve the symptoms.
Multiple types of fish are great snail eaters. Clown loaches are classic, they relish snails. These are “snail-slurpers”; they grab the exposed snail body with their teeth and pull it out of the shell. The shells can be removed at the next vacuuming. Puffers are “snail-crushers”, chewing the beasts up shell and all, ejecting the flakes of shell through their gill or occasionally just spitting out the larger pieces. A number of cichlids and catfish are snail eaters as well. Whether any of these fish are suitable for you or your tanks is a personal decision.
What snails are likely tank inhabitants? I’ll go through the commonest types seen, but for more detail and photos you will have to browse some of the standard aquarium references such as Baensch’s Aquarium Atlas (1).
Malaysian Trumpet Snails: These relatively small snails have deeply spiraled ice-cream-cone shaped shells. An MTS snail with a ¾” shell is large. Most will be smaller. These snails spend most of the daylight hours (read as tanklight hours) burrowed into the gravel if the tank inhabitants harass them in any way, and come out to feed after lights out. Because of this habit, their true numbers may not be obvious. If they are the only snail species you have, go into the room after it has been in total darkness several hours and switch on a light, or just use a hand-held flashlight. Then you will see the true MTS population. These are the most desirable tank snails IME and IMHO. They seem totally harmless to plants but graze happily on green algae and decaying foliage. They do not touch hair or filamentous algae. They are reported (2) to be parthenogenic females, males being either rare or not seen. So these may well be self-cloning organisms, rather like summer Daphnia. They are also livebearing, producing fully formed offspring without an external egg phase. As they have opercula, a sort of trap door they can close after withdrawing their body into the shell, they are more difficult for predators without large strong grinding jaws to eat (the shells are exceptionally heavy and strong relative to their size). They are the one snail type that clown loaches may not be able to eradicate, but they will certainly greatly reduce the population. MTS burrowing is commonly exaggerated on the boards. They are sharply limited in the depths to which they can dig by the oxygen content of the substrate. Few substrates offer sufficient oxygen to allow digging as much as an inch.
Malaysian Trumpet Snail
Common Ramshorns and Red Ramshorns: These snails (Planorbis species) have a flat-coiled shell. The maximum shell diameter is just over ¾”. Unlike the MTS, these are always visible, not minding the light at all. They too are plant-harmless IME. These reproduce by means of the familiar flattened, dense jelly-like egg masses spotted freely on any potentially algae-growing area. These egg masses are clear to light amber in color, with the dark eggs or embryos showing clearly. I have not found a fish that will eat or disturb the egg mass, but there may be such around. Any snail-eating fish will devour the juvenile or adult form of these beasts. They have no opercula, so are available to snail-slurpers and snail-grinders alike. Many fish will devour the small young of these snails, but they can still become population problems in overfed tanks. By the way, they are easy to color select. I have selected for red bodies several times by removing all dark-bodied snails (I raise snails for puffers) from the tank as soon as they are seen. At first you just select for lighter bodies, eventually for reddish, and finally for bright strong red. This strain is suitable trade goods for a decent LFS. I have also had white-bodied ramshorns, but this strain for me is harder to maintain- they seem weak and do not reproduce well (perhaps a desirable trait?), requiring backcrossing to normal colored snails fairly frequently for successful maintenance. These snail are hermaphrodites, each may serve as male or female in a given pairing.
Common Pond Snails: These are perhaps the commonest hitchhikers. They are roughly in the genus Lymnea, but some references use multiple genera for the group. The egg mass is much like the ramshorn’s, but is completely clear in the varieties I have kept. If the egg-layer is small, so will the mass be, and contain only a few embryos, so may escape casual inspection. The shell is rather football shaped, or a somewhat domed coiled turban. Some varieties will abrade the surface of some aquarium plants, and too many of the largest of these snails (1/2 – 3/4″) can lead to visible plant damage. If the largest specimens are removed, so will new damage. IME it seems that snails of this type less than ½” cannot abrade healthy foliage. These have very high reproductive and growth rates, so are dandy for rearing for puffers or other snail-eaters, but watch the maximum size allowed to develop if you value the plants housed with them. Don’t be concerned with removing breeders, these seem capable of reproduction from a very small size onward. Both white and reddish mutants have been observed, but I have not strain-selected these myself.
Apple Snails: This group includes the largest freshwater snails that the hobbyist will encounter. Overall ball-shaped or rounded spiral shells, they are available in a variety of colors for both body and shell. Bizarre and fascinating to watch, these giants are visible from across the room, even to aging eyes. They have snorkels that can be extended to the surface to take in air from above the water surface to supplement their gills. They are large heavy beasts and should be counted as a large heavy fish in tank capacity considerations. They have appetites to match their size, and certain species devour any vegetable matter available, so should not be trusted with any live plants. They are breedable in tanks, but deposit the eggs in a mass above the water surface. The egg mass, appearing like a very tight bunch of very small grapes to a smallish cauliflower rosette, will dry and harden. After ~2-3 weeks the babies will break out and drop into the water if they not over-heated or over-dried in the meantime. These snails are not hermaphroditic. They are either male or female, and both are required for reproduction.
One type of Apple snail, the “mystery snail” is harmless to most plants. It is medium sized for the group and not so deeply incised in the grooves of the spiral as the other common varieties. They too are available in several color forms. I would hesitate to trust most LFS to tell the good guys from the plant eaters.
Gold mystery snail
The “Colombian Ramshorn” is a flat-spiraled snail like a giant version of the common ramshorns discussed above, but far more attractive. It tends to show several dark stripes on the outside of the spiral. This is the only (known) flat-coiled Apple snail, and it too is a plant eater.
Snails can be a boon or a curse, may help keep the tank neat, or may tell you things about your care that you had rather not hear but need to know. They can assist plant growth by moderate substrate stirring and cleaning the leaves of some algae, or devour your favorite plants. They can be specimens in their own right, or unseen workers in the dark. The choice is yours.
This article appeared first on another site. It has been edited for use on this site.
Robert T. Ricketts, a.k.a. RTR