Snails: Friend or Foe in the Aquarium?
By Richard Brown
First published in Tank Talk, Canberra and District Aquarium Society, Australia
Aquarticles
Introduction
Snails have a bad reputation. When I first started keeping fish around 12 years ago, I was
told by many ‘reliable’ sources that snails were bad news: "They will eat
your plants," "they will breed like crazy and turn your tank into a creeping
mass of snails," "they will foul your water." Not surprisingly, for several
years I have treated snails with an amount of disgust and contempt. However, over the last
few years I have discovered that snails are actually a very useful and decorative
creature. I hope the following account will encourage some of you to give snails a go.
The Biology of Snails
Along with creatures such as Clams and Oysters, snails belong to the phylum Mollusca.
A generalised trait of molluscs is that they are soft-bodied creatures lacking supporting
structures such as bones or exoskeletons. The topic of this article, snails, belong to the
class Gastropoda. Gastropods are distinguished by their having a single
shell. This shell is usually coiled and is part of the snail's living body. The
soft-bodied section of the snail can be withdrawn into the shell, thus forming a defence
against predators.
An important thing to know about snails is that they have been on this planet probably
longer than us, the primates, and our pets, the fish, combined. Snails appear in the
fossil record around 500 million years ago. They are easy to find around many of the
limestone cliffs on the Australian coast.
Snails are a very successful species, there are around 80,000 species of snails that
have been identified. The majority of snails, approximately 55,000, can be found in the
marine environment. The remainders are land snails and freshwater snails. Water snails
breathe through gills whereas land snails breathe through a hole in their body near the
base of the shell.
Land snails are hermaphroditic, that is, each snail has both male and female parts.
They still must mate to reproduce, however. A hole near the head is the genital orifice
where the snail mates and also from where it lays its eggs. Aquatic snails have both
hermaphroditic and heterosexual reproduction. Most snails lay eggs, however a notable
exception to this is the Malaysian Trumpet Snail, which is a live-bearer.
The shell of the snail is largely calcium carbonate. This chemical is familiar to
aquarists as the buffering agent that promotes pH stability. As a consequence of this,
snails generally tend to prefer harder and more alkaline water. In fact, acidic water
tends to dissolve the shell and leave its occupant open to attack from predators - either
to the joy or the horror of the fish keeper.
Apart from their shells, other features that generally distinguish gastropods from
other molluscs is that they have an eye located at the base of each tentacle. The
‘foot’ of the snail is a muscular appendage used to ripple its way across its
environment. Under the tentacles is the mouth. Inside the mouth there is a rasp-like
tongue that acts like a saw. It shreds the snails' food much like a grater sheds cheese.
This leads me to a topic that may be of interest in the context of the home aquarium -
snails’ eating habits. The diets of snails vary depending on the species. Indeed,
some snails are carnivorous and will actively hunt down other gastropods. Generally
though, snails eat algae, plants, and on occasion the decomposing flesh of dead animals.
The Advantages of Snails
The fact that snails eat algae and decomposing flesh can be of great benefit to the
aquarium keeper. I am sure that many of you keep Bristlenoses and other algae eating
catfish. While I do not want to criticise these valued fish, for they do make fantastic
pets in themselves, their algae eating capacities are often over estimated by their
owners. Snails however are very thorough cleaners of glass and rocks and can get into the
nooks and crannies that catfish may miss.
Some species of snail are renowned as decorative plant eaters, however, in my opinion,
only the pond snail should be regarded with any real suspicion in this regard. Most
healthy aquarium plants produce cyanides and other poisons that prevent animals such as
snails from making meals of them. The myth that snails can destroy your plants probably
originates from observations of snails eating the leaves of plants that are already highly
deteriorated or close to dying. At this point, the plant was probably doomed and at least
the snails are preventing the plant from decomposing, a process that can potentially
unbalance aquarium water chemistry.
Another great advantage of snails is that they are less likely to eat the eggs of fish.
While eggs laid by fish in or around the substrate of the aquarium are vulnerable to
attack by Bristlenoses and the like, snails are much less likely to embark on such raiding
excursions. Consequently, if you are keeping egg-laying fish in a tank with alkaline water
specifically for the purpose of breeding then snails are probably the solution. They will
keep maintenance down by cleaning your glass but will not scoff the eggs at the first
opportunity. For instance, I am currently keeping a breeding pair of Neolamprologus
ocellatus in a two foot tank and rather than keeping Bristlenoses, I have a
crew of Red Ramshorns to keep the tank clean. Interestingly enough, in nature these little
cichlids, which originate from the hard waters of Lake Tanganyika, adopt used snail shells
as their homes. They keep their shells immaculately clean, hide in them when threatened
and eventually lay eggs and raise their young in them. Although they are brave little
fish, the heavily armoured Bristlenoses that I keep tend to be oblivious to the attacks of
the ocellatus, presumably their eggs would be helpless at night.
Lastly, snails make interesting and hardy pets in themselves. They can be quite
attractive, especially in the case of the Mystery Snail. They also have interesting habits
and life cycles.
The Disadvantages of Snails
There is no doubt that snails can get out of control. Unfortunately, given the right
conditions of hard alkaline water and without natural predators, snails can multiply very
rapidly. I have experienced this first hand in the case of the Malaysian Trumpet Snail.
Several years ago, in a four foot Malawi tank that I was keeping at about 250 ppm of total
carbonate hardness, the floor of the tank almost seemed alive. The plague of snails was
most unsightly and remedial action was called for.
There are several ways to keep snails in check:
· The “predator” method. Several species of fish just love snails, for
breakfast that is. The most common snail eater is the attractive Clown Loach, Botia
macracanthus. The Clown Loach will grab the unprotected soft part of the snail and
literally suck the poor gastropod out of the shell. If you don’t mind me saying, this
can be quite entertaining. In the marine tank, Pufferfish are good snail eaters and will
crunch the shell of the snail and eat the soft parts. In fact, some people grow snails
specifically to feed to their Clown Loaches and Pufferfishes. I have to admit that my Red
Ramshorns live side by side with a healthy Clown Loach. Perhaps I overfeed him.
· The “bait” method. Run some hot water over a lettuce leaf and just before
you turn the lights out, tie a piece of cotton around it and drop it in the tank. It will
sink to the bottom and in the morning you should find it covered in snails. Remove the
lettuce, snails and all. Repeat until the snails are under control. In fact, this was the
method that I used to remedy my Malaysian Trumpet Snail problem. Needless to say,
persistence may be called for.
· The “starvation” method. It is important to note that most snail blooms
are caused by overfeeding. In these cases, the only reason that the snails are
overpopulating is because they are feeding on the excess food that the fish leave behind.
Watch your fish when feeding, if they do not eat all their food after 3-4 minutes or less
then you are overfeeding.
· The “local fish shop” method. There are some commercial snail killers
available that local fish shop owners might try to sell you. If used as instructed these
remedies may well kill your snails. However, these chemical based solutions should be
avoided because they tend to kill the bacteria that keep ammonia and nitrite levels in
check. In turn, this may also kill your fish.
Prevention is usually better than the cure. If buying plants from a local fish shop or
even at a CDAS meeting and you don’t want to accommodate any hitchhikers then I
suggest that you take the following action. Before introducing your plants into the
aquarium, make the effort of soaking them in warm salty water. After ten minutes remove
the plants and wash thoroughly. This should remove or kill any unwanted gastropod guests.
It will also remove potentially harmful parasites such as White Spot (Ich).
Conclusion
I have to admit that despite my first impressions, I am now very happy to see a few snails
in my aquarium. When kept in check, they can form an integral part of a well balanced
aquatic environment. So, why not give snails a go?
|