Unwanted pest animals

Aiptasia (Glass anemone)

Also called "rock anemone", it belongs to the family Aiptasiidae, which currently contains 12 species; the most common are:

• Aiptasia pallida = translucent, it can be white or deep yellow/brown
• Aiptasia pulchella = brownish, even pale, with lighter tentacle tips
• Aiptasia diaphana = brown or pink/reddish with lighter tips and generally smaller than the others (no more than 3 cm)
• Aiptasia mutabilis = the only cold-water Aiptasia, larger than average (it can reach 12 cm), brown or yellow/brown with green or blue lines running from the mouth.

1. 1Aiptasia pallida translucent, white or deep yellow/brown
2. 2Aiptasia pulchella brownish, lighter tentacle tips
3. 3Aiptasia diaphana brown or pink/reddish, no more than 3 cm
4. 4Aiptasia mutabilis up to 12 cm, green or blue lines from the mouth

The article gives its own size only for diaphana and mutabilis: the other two are drawn at 5 cm, the maximum height given in general.

What it looks like

Aiptasia can reach a height of 5 cm, but in most cases it stays at about 2.5 cm. Its structure is made up of a foot, a long, thin column and an oral disc with a central mouth.

Around the edge of the oral disc there are 100 stinging tentacles, which alternate with one another and which it uses to defend itself by releasing a venomous substance contained in the nematocysts.

It also defends itself with dangerous white threads called acontia.

1. 1Foot anchors it to the rock and lets it move
2. 2Column long and thin; its colour comes from zooxanthellae
3. 3Oral disc carries the mouth and tentacles
4. 4Mouth in the centre of the disc
5. 5Stinging tentacles about 100, with venom in the nematocysts
6. 6Acontia white defensive threads

It can reach 5 cm, but in most cases stays at about 2.5 cm.

How it moves and spreads

The glass anemone anchors itself to the mostly rocky substrate with its foot and, if over time it no longer feels comfortable, uses it to move (about 4 cm an hour); but it can also detach and float in the water until it finds a place to anchor.

Since it is very small at birth, it hides very easily in rock crevices by turning into a little ball, and it can stay dormant even for a few months.

It can be added to the aquarium by accident on rocks or coral frag plugs and, since it reproduces very fast (it produces a dozen specimens in a single day), you should act as soon as possible to remove it with natural antagonists and/or by chemical or physical removal.

1. 1Sneaks in on rocks or coral frag plugs
2. 2Turns into a little ball in crevices, dormant even for months
3. 3Moves with its foot about 4 cm an hour
4. 4Floats in the water until it finds a place to anchor
5. 5Multiplies fast a dozen specimens in a day

You should act as soon as possible.

Of course it does not enjoy a very good reputation among marine aquarium enthusiasts; it is a real parasite that spreads very quickly, even killing invertebrates and small fish with its venomous tentacles.

It is a carnivorous animal: it feeds on zooplankton and particles suspended in the water, but it also gets food through its zooxanthellae, which are also what give it its colour.

Natural antagonists

Shrimps =

• Rhynchocinetes uritai
• Rhynchocinetes durbanensis
• Lysmata wurdemanni
• Lysmata boggessi

Nudibranch Berghia verrucicornis

Fish =

• Acreichthys tomentosus
• Chaetodon burgessi
• Chaetodon auriga
• Chaetodon lunula
• Chaetodon kleinii
• Chelmon rostratus

One point must be stressed about these Aiptasia predators: most of them are very hard to feed (once the glass anemones are gone) and to acclimatise, or they may not be very reef safe, or you may not have a tank of the right size for them to grow in the best conditions.

So weigh your choice carefully, especially if it involves butterflyfish.

Physical/chemical removal

You absolutely cannot think of removing an Aiptasia by scraping it off the rock, cutting it or crushing it, because even a single tiny fragment left behind will grow into a new specimen.

There are, however, other methods that can keep it under control, such as liquid chemical products (like Aiptasia X) or pastes which, placed on or into the mouth of the individual animal, can kill it; we are talking about compounds made of calcium and/or lime, well tolerated by the aquarium but to be handled with care, wearing gloves, because they can be caustic.

One of these, the most used, is kalkwasser paste: mixed with RO water to a toothpaste-like consistency and placed over the Aiptasia's mouth, it will dissolve it.

You can also use epoxy resin so as to trap the animal in the rock.

Another method within everyone's reach, because it is always in the house, is to use boiling white vinegar to inject the animal with a syringe, taking care to pierce it deeply with the needle.

1. 1Scraping, cutting or crushing: don't
2. 2A single fragment grows into a new specimen
3. 3Paste on the mouth kalkwasser in RO water, like toothpaste
4. 4Epoxy resin traps the animal in the rock
5. 5Boiling white vinegar needle in deep: handle with care

The methods that work hit the whole Aiptasia: one fragment left behind is enough to start again.

Majano (Anemonia manjano)

Rather small sea anemones (about 1.5 cm) of the family Actiniidae, they are much prettier than their Aiptasia cousins.

So far 22 species have been recognised. They too can get into the aquarium by accident, on rocks or coral frag plugs, and they can be very invasive and dangerous for fish and invertebrates, because they sting and are venomous just like Aiptasia.

They are brown/greenish, and the tentacles have green, white or otherwise light tips, rounded or pointed depending on conditions.

They move and anchor themselves with a sticky foot, sticking to anything (in our aquariums, equipment, glass, rocks and so on).

They feed through their zooxanthellae but, being carnivores, they also eat zooplankton.

Natural predators

Shrimp Lysmata wurdemanni

Fish =

• Centropyge (dwarf angelfish)
• The genus Apolemichthys (angelfish)
• The genus Pomacanthus
• Acreichthys tomentosus

With these fish too, you have to bear in mind their feeding habits and whether we have an aquarium big enough to house them in the future.

1. 1Shrimps Rhynchocinetes uritai, R. durbanensis, Lysmata boggessi
2. 2Nudibranch Berghia verrucicornis
3. 3Butterflyfish Chaetodon burgessi, C. auriga, C. lunula, C. kleinii, Chelmon rostratus
4. 4Lysmata wurdemanni shrimp listed for both
5. 5Acreichthys tomentosus fish listed for both
6. 6Angelfish Centropyge, Apolemichthys, Pomacanthus

Before choosing, think about afterwards: many are hard to feed and need a big tank.

Physical/chemical removal

Majano can also be removed by hand, and in this case the same techniques and products listed above for Aiptasia are used.

Article written by: Loredana Prologo

Sources

1. WoRMS Editorial Board (2026). Exaiptasia diaphana (Rapp, 1829). World Register of Marine Species.
2. WoRMS Editorial Board (2026). Aiptasia mutabilis (Gravenhorst, 1831). World Register of Marine Species.
3. WoRMS Editorial Board (2026). Anemonia manjano Carlgren, 1900. World Register of Marine Species.
4. Fofonoff P.W., Ruiz G.M., Steves B., Simkanin C., Carlton J.T. (2018). Exaiptasia pallida, NEMESIS species profile. Smithsonian Environmental Research Center.
5. NIOSH (2019). Pocket Guide to Chemical Hazards: Calcium hydroxide. Centers for Disease Control and Prevention.