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Ciliate colonies appearing out of thin air?

caridina English Edition - epaper ⋅ Ausgabe 3/2019 vom 30.07.2019

A closer look at vorticellids, and an assessment if they are a threator not

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Bildquelle: caridina English Edition, Ausgabe 3/2019

Vorticella on a dwarf shrimp.

Photo: Chris Lukhaup

The bell-shaped sessile animalcules from the Vorticellidae family can be found in aquariums from time to time, especially in newly set-up tanks. Per se, they are not really dangerous, and there is no urgent need for countermeasures, however, they may be a sign of impending problems – especially in a tank with less robust shrimp –, and therefore they merit a closer look.

Bell animalcules, aka vorticellids, are unicellular organisms that belong to the ciliates and live in ...

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... freshwater habitats. Their trivial name refers to the bell-shaped “head”, sitting on a very slender stalk. The upper fringe of the “bell” is seamed with tiny bristles, or cilia, which these tiny animalcules use to create a vortex that transports food into their mouth opening – hence the name “vorticellids”, or Vorticellidae. They mainly eat microorganisms, mostly bacteria. The stalk ends in an adhesion pad which holds the ciliate in place.

The members of the Vorticellidae family can loosen these adhesion pads from its substrate, and swim freely – but quite slowly – through the water by beating their cilia, to reach new areas to settle on. Some species can contract their stalk in a spiralling way. If you touch such a colony you can perceive a wave-like movement. Vorticellids reproduce through cell division or through budding, like all ciliates. There are several genera in this family, likeVorticella ,Carchesium ,Rhabdostyla orEpistylis .


Vorticellids usually sit on the aquarium decoration, the plants or the glass, but they can also occur on the exoskeleton of shrimp or crayfish, on snail shells and even – though less frequently – on fish, and even on worms. Individual specimens are very small and slender, so they usually go unnoticed. You will only find them if you are looking for them, as they grow to only 0.25 mm in size.

However, there are quite a few vorticellids that form colonies, and those are quite easy to detect: They are whitish to beige and look a bit like mildew. Small colonies consist only of a few specimens, but large colonies may cover an area of several centimeters in length. Those often have a cloud-like appearance. If you look closely, you can see the “heads” of the bell animalcules as tiny white spots within the cloud.

Schematic drawing ofCarchesium polypinum .

Drawing: Popular Science Monthly Volume 5, 1874

Vorticellids on the aquarium glass, next to a daphnia (Daphnia pulex ).

Photo: Oliver Mengedoht

Quite frequently, vorticellids are called “parasites” or “(faux) shrimp mold” – an absolutely unnecessary alarmism, since they have nothing in common with mold, and they are not a parasite! They merely sit on the carapace of the shrimp or crayfish without doing any harm: they are strictly ectocommensal organisms. With the possible exception of fish skin they won’t damage the substrate they are sitting on. The mucous membrane of a fish can indeed be harmed by vorticellids clinging to it, which makes the fish susceptible for secondary skin infections.

When their habitat starts to deteriorate, if the waterbody dries out or food gets scarce, vorticellids can encapsulate, thus forming a cyst, which is so light in weight that it can be carried away by the wind and becomes part of the natural dust. In nature, this is a great strategy to reach a new biotope, and at the same time this is also how vorticellids find their way into our aquaria – they literally come out of thin air!

Bell animalcules magnified by the factor 160; the L-shaped structure is the nucleus.

Photo: Picturepest-CCBY20

Vorticella campanula sitting on an a

Photo: Giuseppe Vago / CC-BY 2.0

Of course you can also introduce them as they sit on invertebrates, plants or decoration from running aquaria. A small number of these tiny organisms in the aquarium is absolutely no reason to worry, they are a normal part of the biotope, and play an important role in the ecosystem as they keep the bacteria population in check.

Vorticellidae on the shell of a Common Ramshorn Snail (Planorbis planorbis ) in a pond at Kirchwerder, Hamburg, Germany.

Photo: Aiwok CC BY-SA 3.0


However, if the number of bacteria in the tank grows extremely, the vorticellids may also reproduce in high numbers. This is the reason why you usually see large colonies in cycling tanks, or if something goes wrong in the ecosystem so a high number of bacteria accumulate in the water. You can often detect vorticellid colonies in places with a high nutrient density, like the feeding areas of crayfish, for example.

Therefore, an “infection” with vorticellids can be an early warning signal. A high concentration of germs in the aquarium water often goes unnoticed, but may do great harm to less robust shrimp that need very clean water, like e.g. Bee shrimp, Tiger shrimp and their hybrids like Shadow Bees, the new shrimp breeds like Boa or Red Devil and so on. If you notice the presence of a large number of vorticellids in such a tank you need to act, and fast!


There is no need to eradicate the vorticellids directly, though, so you won’t need to dose the tank with medication, as some sources recommend. We want to fightthe reason, not the symptom, after all! This means you’ll have to lower the germ concentration in the water. As a rule, it depends on the presence of nutrients in the water, which increases when aquarium hygiene is a bit sloppy, or when the tank is overfed. An easy first step to lower the germ concentration is a large water change.

As second step, critically inspect your feeding habits. Quite frequently, aquarium pets are overfed. In nature, shrimp mainly eat detritus, biofilms, brown tree leaves that fell into the water, and of course (more rarely) insect larvae or even a bit of dead fish or other shrimp, worms and such. If you already feed sparingly, you may want to look into the food quality – high-quality food is digested better, which usually results in a lower organic load.

Besides regular water changes, mucking off the substrate may also lower the germ concentration in the tank. Especially in the feeding area, leftovers seep into the ground, on which the bacteria feed. Removing dead plant parts and – of course – dead animals may also reduce the bacterial load. If you carry out these measures diligently, you can literally watch the vorticella decline and disappear all by themselves.

The structure ofVorticella convallaria (A), the vortex created by the cilia (B) and a series depictingV. convallaria contracting its stalk into a spiral within microseconds.

@@Vorticella (small, upper left) and trumpet animalcules on the leaf of an aquatic plant.

Photo: Oliver Mengedoht