Anemonefishes (aka clownfishes) have long been the darlings of the marine aquarium hobby. Not only are most of them attractive in color, but their amazing partnership with the “flowers of the sea” – the sea anemones – makes them fascinating additions to one’s captive ocean. While most anemonefishes are well-suited to life in the marine aquarium (especially captive-raised individuals, which are now readily available), their invertebrate hosts are not always that easy to maintain over the long haul.
Sea Anemones and Their Care
Sea anemones (phylum Cnidaria, class Anthozoa) are unusual animals with a simple body plan. They consist of a base (which is attached to the substrate), a column and a disc. The disc is where the mouth and tentacles are located. The tentacles are armed with stinging cells that are used to fend off most predators and also to capture small prey. Not all sea anemones available to anemonefishes are adopted by them as hosts. To date, 10 different species from five different genera have been found harboring anemonefishes in nature. The hosting anemones are relatively large species (from 8 to 39 inches in diameter), but their shape and tentacle structure can differ considerably. Some have long tentacles (e.g., Heteractis spp.), while others have short, stubby tentacles (e.g., Stichodactyla spp.). The color of these anemones can vary between and even within a species. For example, the magnificent sea anemone (Heteractis magnifica) can have a brown, green, pink, orange or even scarlet-red base.
Anemonefishes that inhabit sea anemones are all residents of coral reefs in the Indo-Pacific, and all inhabit relatively shallow water. The reason they are most common at lesser depths is because these anemones host zooxanthellae (dinoflagellate algae) in their tissues. These algae species require the intense rays of the sun to photosynthesize, the byproducts of which provide nutrients for their sea anemone host. The result is that these sea anemones are limited to clear, shallow, sunlit waters where their symbiotic algae partners can thrive.
In my experience, the two keys to successful anemone care are strong lighting and adequate water movement. If you are serious about keeping clownfish-hosting sea anemones, purchase the best lighting system you can afford (e.g., metal halide, high output or very high output fluorescent lighting systems). Anemones also need strong water movement, which serves to oxygenate their tissues and wash away waste products. When providing water flow for your cnidarians, make sure that the intake of the water pump has a strainer or sponge barrier to prevent the anemone from getting into the pump’s impeller. It is not uncommon for an anemone to insert its tentacles or base into the intake opening of a water pump; the impeller will lacerate the tentacles, which will kill the anemone. The propeller-type pumps are great for producing a more gentle flow. Those sea anemones that tend to wander a lot are also prone to migrating over overflow boxes. This can plug up the overflow and cause flooding problems.
Another thing to remember when keeping anemones is that not all species come from the same habitat. Some prefer to attach to hard substrates, while others plunge their bases into soft sediments. (You will find notes in the species accounts in this article regarding the various species’ microhabitat preferences.) Make sure you meet these microhabitat preferences in your aquarium.
Not all aquarists feed their sea anemones, relying instead on the “solar-powered” algae in the anemone’s tissues to provide needed nutrients. Yet supplemental feeding of your sea anemone is a good idea. They will eat finely chopped seafood (shrimp, clam, marine fish flesh) and mysid shrimp. Simply place the food among the tentacles once or twice a week. Some species may also prey on their fish neighbors. For example, members of the genus Stichodactyla can be dangerous to tankmates, catching and consuming careless or startled fish. This often occurs at night when the lights go off and the fish are moving about the aquarium trying to find refuge.
It is important that an anemone is not harmed when it is removed from a holding tank (especially species that attach to hard substrate). If the base is ripped during the removal process, it can open a site for bacterial infections and cause death. One way to remove the sea anemone from the rockwork (or the aquarium glass) is to use the edge of a credit card (this should be done carefully). Some aquarists suggest placing an ice cube against the base, which is said to eventually cause the anemone to release its grip (I have never tried this). If the anemone is attached to a small piece of rock, I recommend taking the rock along with the anemone.
Anemones in the Trade
All of the anemone species that host anemonefishes are available in the aquarium trade, though some are more common than others, and some do better in captivity than others. What follows are eight of the most common species in the hobby.
1. Adhesive sea anemone (Cryptodendrum adhaesivum).
This anemone is often sold as the “pizza anemone” because it is flat and has a ridge around the edge that looks like pizza crust. One of the downsides with this species is that it has a potent sting. When you touch it, the short tentacles feel sticky, while if you contact more delicate areas of skin (e.g., your wrist), it can cause welts. This “sticky” feeling is the anemone’s sting, and though it may not hurt a human, some anemone stings can be detrimental to some aquatic animals. The “crust” of the anemone can be a combination of yellow and pink, blue and gray, green and brown or gray and purple. Cryptodendrum adhaesivum is unique in that the tentacles differ in shape: some are branched, while others have a bulbous tip, and the column has rows of bumps (verrucae) that can be white, orange or yellow.
The normal habitats of this species are shallow fringing reefs or patch reefs, where C. adhaesivum sticks its base in holes, crevices or under rocks. The pizza anemone occasionally hosts the nonfussy Clark’s anemonefish (Amphiprion clarkii), but it is often home to commensal crustaceans. The adhesive anemone is a hardy aquarium species, but be aware that it has a potent enough sting that it can catch and eat fish tankmates. It is also not usually a welcome addition in a reef aquarium because it will fatally sting any coral it contacts.
2. Bulb anemone (Entacmaea quadricolor)
. One of the most often encountered host anemones in the aquarium trade is the bulb tentacle or bulb anemone. This species gets its name from its tentacles, which have a bulblike tip (their appearance can differ, depending on how expanded or contracted they are). The column is usually brown, while the oral disc and tentacles can be green, brown or even fluorescent orange (these are usually referred to as rose anemones).
There are two different types of E. quadricolor: a larger solitary form and a smaller colonial form. This species is one of the anemones that is better-suited for aquarium life, with the colonial form being especially durable (colonial individuals are typically the small individuals you see at fish stores). The colonial form will often reproduce asexually in captivity, with one anemone splitting into two. This can occur when life is going particularly well for your anemone or when they are especially stressed.
It turns out that Entacmaea are not only popular with aquarists, but they are also one of the most “popular” cnidarians with anemonefish species (13 different anemonefish species having been reported to utilize it as a host in the wild and a few more do so in the aquarium). The bulb tentacle anemone usually inserts its base deep into reef crevices and will retract into these interstices if threatened. This species usually is fairly well-behaved in the reef aquarium, as its sting is not as potent as many other anemones.
3. Beaded anemone (Heteractis aurora)
. The beaded or aurora sea anemone is easily recognized by its beautiful tentacles, which have a series of beadlike swellings along their length. The column is often pale with orange or red mottling, becoming more pale toward the disc. There are relatively few tentacles, which means much of the disc is exposed. The disc often has white radiating lines. The color of the tentacles and oral disc can be brown, greenish, creamy or purplish with light spots. Heteractis aurora shoves its base into sand or gravel, rather than a hard substrate. It will retract into the substrate when threatened. On rare occasions, individuals may adhere to coral rock.
This species is a host for seven different anemonefishes and most often harbors juvenile Amphiprion, which use it as a temporary sanctuary before moving to a more preferred, larger cnidarian host. The beaded sea anemone is relatively easy to keep if provided with a thick sandbed and good illumination. It tends to prefer the sandbed, so it is less likely to contact corals on the rockwork.
4. Leathery anemone (Heteractis crispa)
. The leathery or sebae anemone is another common species in the aquarium trade. It has a gray column and a leathery appearance. The disc and tentacles can be brownish, gray, mauve or green. The numerous tentacles, which are long and sinuous, often have purple or pink tips (captive individuals are often bleached out and are white in color). This sea anemone usually attaches itself to reef or rubble substrates. It may also be found with its base buried in the sand; in this case, the base is attached to subsurface rocks or rubble. This is a popular host for anemonefishes and crustaceans, with 14 species of anemonefishes having been reported among its tentacles in the wild. If a healthy H. crispa can be acquired, it tends to do well in the aquarium. It can suffer from shipping stress; stressed individuals eject their zooxanthellae during transport and are pure white.
5. Magnificent sea anemone (Heteractis magnifica)
. This anemone is one of the most beautiful species available to aquarists, but it is also one of the most difficult to keep. The column of this species can be magenta, blue, red, brown, green or white. The tentacles and oral disc are usually shades of brown but can be yellow, green or white. The tentacles are fingerlike, and some may be branched. Heteractis magnifica can occur singly or in groups (in some cases, these groups can cover large areas). These assemblages are the result of asexual reproduction. This is a beautiful sea anemone that is only found on hard structures. It usually sits in exposed areas, and it does not stick its base into reef crevices. When it is threatened, it pulls in all of its tentacles and forms a large ball. It is popular with anemonefishes, harboring 12 species, and is also home to a number of crustaceans. Unfortunately, this beautiful anemone is difficult to keep. It tends to be a vagabond in captivity, roaming about the aquarium in what appears to be an attempt to find a preferable microhabitat. This often means the anemone often contacts other stinging creatures, gets its tentacles sucked up into intake tubes, or stuck against or in overflow boxes.
6. Corkscrew anemone(Macrodactyla doreensis)
. This anemone has a column that is often dull orange or red with rows of small bumps (verrucae) running upward. The oral disc and tentacles can be green, cream-colored or even purple. The tentacles are long and sometimes exhibit a corkscrew shape. Macrodactyla doreensis lives on soft substrates and will bury its base and column in the sand, mud or gravel bottoms (it is also found on mixed-rubble-sand substrate). It will retract into the substrate when disturbed. This sea anemone is a host to only three anemonefish species (including Clark’s and the pink skunk anemonefish). This anemone is a hardy aquarium inhabitant if provided with a suitable habitat (e.g., thick sandbed and good lighting).
7. Haddon’s carpet anemone (Stichodactyla haddoni)
. Like all the members of the genus Stichodactyla, which are known collectively as carpet anemones, Haddon’s carpet anemone has relatively short tentacles. The tentacles of the Haddon’s carpet anemone are very short and round. The nematocysts pack a fierce punch and feel sticky to the human hand. The disc is usually quite convoluted. The disc can be yellow, green or tan, and it does not have heavy folds (as per Stichodactyla gigantea and S. mertensii – two species that are difficult to keep). The tentacle tips can be green, yellow, gray or (on rare occasions) pink. This species is a resident of sand or gravel substrates. It plunges its base and column into the substrate, and when threatened, it will pull under the sand surface. Occasionally, it will attach to bare coral rock.
There are six anemonefishes that will live in this anemone. While most of the carpet anemones are difficult to keep, this species does quite well in captivity if provided with high-intensity lighting and a moderately deep sandbed in which to sink its base.
8. Giant carpet anemone (Stichodactyla gigantea)
. This anemone has a deeply folded disc with short tentacles. The tentacles have a tapered end and can be brown, greenish, purple, pink, deep blue or bright green. The oral disc is often tan or pink, while the column is tan, gray, green, yellowish, blue or maroon. Another unusual characteristic is that the tentacles often look like they are vibrating. S. gigantica ranges from the Red Sea to Micronesia.
The giant carpet anemone prefers sandy, shallow habitats. It plunges its base into the sand and will retract under the substrate surface if threatened. It occurs from the intertidal zone to depths of at least 16 feet. It most often occurs in protected lagoons, including sea grass meadows. Stichodactyla gigantea serves as a host to seven species of anemonefishes and a number of crustacean species. This is a difficult species to keep in captivity, often suffering from shipping stress and lethal bacterial infections.
Not only do anemonefishes adopt sea anemones that they do not naturally occur with, they will also make their home among the tentacles of long-tentacled corals in an aquarium where natural hosts are not present.
Some stony corals that are known surrogate hosts include members of the genera Alveopora, Catalaphyllia, Euphyllia and Goniopora. Most of these species have long tentacles or polyps that are reminiscent of a clownfish’s sea anemone host. In most cases, when the coral colony is in good shape, the anemonefishes do not appear to harm their coral host. But anemonefishes may cause polyps to contract when they bathe in the tentacles or even nip at them. If the coral is in bad shape, the anemonefish’s activities could push it over the edge.
Anemonefishes will also wallow among the tentacles of certain soft corals (e.g., Anthelia, Sarcophyton, Xenia) and zoanthids. They may even adopt mushroom anemones (corallimorpharians) as a host, especially those that are “hairy” (i.e., have tentacles on the disc). As with stony corals, they usually do not harm these cnidarians.
Finally, there are some anemonefishes that will even adopt noncnidarians as a host. I have seen young clownfish living with the tentacular crown of feather duster worms and have also had these fish adopt patches of filamentous algae as a surrogate anemone.
Other Anemone Hosts
In captivity, anemonefishes have been known to adopt nonsympatric sea anemones as hosts (anemones that do not occur with them in the wild). The most commonly utilized nonsympatric anemone is the pink-tipped or giant sea anemone (Condylactis gigantea), a large, long-tentacled cnidarian from the tropical Atlantic. In the aquarium, certain anemonefishes will acclimate and live in this anemone. The species that most often do this are Clark’s anemonefish (A. clarkii), which is the least selective anemonefish, and the maroon anemonefish (Premnas biaculeatus). The maroon anemonefish is almost always found in the bulb tentacle sea anemone (Entacmaea quadricolor) in nature.
That ends our survey of the fish-hosting sea anemones. With proper care, these animals can live for decades in the home aquarium (they are thought to live for more than 100 years in the wild), and along with their anemonefish associates, can provide the aquarist with many hours of fun and fascination. Happy fish-watching!
Scott W. Michael is the author of “Reef Sharks and Rays of the World,” as well as “Reef Fishes: A Guide to Their Identification, Behavior and Captive Care” and more. His photos have appeared in publications around the world.