Fish Articles

Anemones in Captive Systems

By Robert Fenner

Flowers of the sea? Hardly. Most anemones are marine; but they are definitely animals, just a step or two up from the "tissue-grade" life that is the sponges, phylum Porifera. The trade in these stinging-celled animals is brisk, and well it should be; many species are reasonably available and hardy, undemanding aquarium fare. This article deals with the natural history and captive care of the polypoid cnidarians (coelenterates) we call anemones.

Try imagining a reef system, photograph, television show, fish store without anemones. Hard to do, isn't it? Anemones are seemingly ubiquitous fixtures in all these.

Why? Many species make hardy specimens given proper collection, treatment and selection (by you). They have remarkable, interesting biologies.

Classification: Taxonomy, Problems

Early classifiers termed anemones "zoophytes" or animal plants, in reference to their flower-like appearance. Many of us know them from their old phyletic grouping within the "Coelenterata, an allusion to their gastrovascular cavity (coel= hollow, enteron= intestine). Modern classifications tend to leave out the comb-jellies (phylum Ctenophora), and group the anemones, jellyfish, hydras and corals as the phylum Cnidaria, describing their "possession of stinging-cells" on mouth-surrounding tentacles.

Within the phylum they are further sub-classified on the basis of body plan. Anemones are typically polyp-like (polypoid) cylinders, sessile, with their oral cavities upright. Other forms are generally medusa-like, free-swimming discs, mouth down.

Most are marine, a few freshwater, some interstitial (in the substate!). There are about 9,000 described species. Their fossil record dates back to earliest life time, the Cambrian period.

Within the Cnidaria, Anemones are placed in the Class Anthozoa; as single or colonial polyps, the medusoid stage completely missing. This group includes the bulk of cnidarian species (6000+) encompassing corals, sea fans, and sea pansies They are distinguished from the hydrozoans and scyphozoans by the lack of an operculum on their stinging cells and several structural/embryological differences.

Anenomes are separated from other anthozoans in the sub-class Zoantharia, and two main orders: The Actinaria are often called the "true anemones". They have internal seperations of body parts (mesenteries) arranged in hexamerous (six) cycles and usually with two ciliated oral cavities (siphonoglyphs). The other order, Ceriantharia, or "tube" anemones have greatly elongate bodies without pasal discs, secreted mucous tubes buried in soft substrates. One siphonoglyph and complete mesenteries.

Relation with other groups:

Placed a group above the sponges, Cnidarians are often grouped with the comb-jellies, phylum Ctenophora as the Radiata, for their radial symmetry. These are simple animals made of three basic layers, an outer epidermis, a lining of the gut (gastrodermis) and a changeable, amorphous inner layer of mesoglea. Cnidarians have little to no organ development.

Selection: General to Specific:

As faithful followers of my unending scribblings will testify, I will not abide nefarious practices in the aquatics trades and, unfortunately, dear reader, anemones are a "guilty" area.

Most anemones that die quickly in the hobbyists care were doomed through mis-collection or rough handling inbetween their purchase. I am referring to physically tearing the body, usually the disc/foot through hasty seperation from the wild substrate or aquarium. Where removing anemones goes, careful patience is key. Some thoughtful, conscientious wholesalers (e.g. Phil Shane's Quality Marine) have hit upon the use of indoor/outdoor carpeting material lining their tanks to facilitate removal and examination. But the ultimate damage born is due to too anxious handling. Carefully, slowly slide a nail under the disc, around the perimeter to remove a specimen. Examine and bag same under water! Avoid having anemones or their "slime" touching your wrists, eyes, other non-calloused areas, especially mucus membranes Rinse and wipe off your hands. Most folks can tolerate time to time contact with most offered species; should you develop a sensitivity, wear thin rubber gloves, or keep your hands off!

Colored Anemones:

Yes; tinted, dyed, artificially colored specimens. "Sebae" and "ritteri" anemones in particular are often adulterated with vegetable (and other) dyes to "enhance" their saleability. I put these (and the people who buy them) in the same box as "painted" fishes, minnows (Labeo, et al.), glassfish (Chanda), and (barf) others. No, the "pretty" color does not last and no, I cannot see how it adds to the organism's vitality. There are naturally colored anemones.

Healthy specimens have long, fully expanded tentacles and a semi-clean earthy/marine smell. Dead, dying specimens smell bad.

If you are comfortable with the varieties you'd like and how you will care for them, specimens can be bought at local outlets, ordered through the mail/phone or even collected from the wild if not too dear or restricted by law. I offer my usual advice for purchase. Inquire as to origin, history on-site... and put down a suitable deposit, retrieving the individual(s) in a week or two. This will weed out the vast majority of doomed/damaged specimens and afford other folks the opportunity of viewing.

Anemones Naturally Symbiotic With Clownfishes:

Cryptodendrum adhaesivum (Klunzinger 1877), the Adhesive Sea Anemone, aka as the Pizza Anemone for obvious reasons. Not often seen or, used in the aquarium interest due to the species extremely sticky short tentacles and propensity for tearing in moving. Only one Clownfish species found in it in the wild, the Clarkii. This specimen in Pulau Redang, Malaysia.
Entacmaea quadricolor (Ruppell & Leuckart 1828), the Bubble-Tip or Bulb-Tentacle Sea Anemone.  This is historically the hardiest of large, naturally symbiotic Clownfish anemones for aquarium use... many more specimens are collected and received intact, in reasonably good health from the wild to distributors. Seen below are a colonial grouping and a close-up image of the Bubble-Tip Anemone and the Clownfish, Amphiprion bicinctus in the Red Sea, and an unusual colored specimen in Pulau Redang, Malaysia
Heteractis aurora  (Quoy & Gaimard 1833), the Beaded Sea Anemone. Up to two inch tentacles with characteristic beaded appearance. With apparent mouth opening and often with radiating appearance from center. Stalk may be mottled or solid orange or red. Live attached to solid structure, able to retract completely beneath the substrate. Full size and close up Malaysian  images.
Heteractis crispa (Ehrenberg 1834), the Leathery Sea Anemone. Often mis-sold/identified in the trade as H. ritteri. Has numerous long, tapering tentacles that end in points. Column gray in color. The first one here in Egypt's Red Sea, the second in the Cook Islands. See more typical aquarium specimen above.
Heteractis magnifica (Wuoy & Gaimard 1833), the Magnificent Sea Anemone. Found in open areas, attached to a solid object. Base of solid purple, blue, green, red, white or brown color. Oral disc flat with barely tapering, finger-like tentacles up to a meter across. Specimens below showing the range of disc and basal color and one open in Pulau Redang, Malaysia at right.
Heteractis malu (Haddon & Shackleton 1893), the Delicate Sea Anemone. Narrow, buried column of pale cream to yellow color, sometimes with some yellow or orange splotching. Upper part with adhesive verrucae  in rows. Sparse tentacles of stubby appearance, variable length, usually magenta tipped, with radial markings. Sound in sediment in shallow, still water.
Macrodactyla doreensis (Quoy & Gaimard 1833), the Corkscrew Tentacle Sea Anemone. Column colored dull orange to red on lower part, to white above, buried in sediment that it can completely retract into. Oral disc flared widely, with few, but long sinewy, tapering, corkscrew-like tentacles. Distinctive (eye-like) verrucae in rows Disc often with radial appearance.
Stichodactyla gigantea (Forsskal 1775), the Gigantic (Carpet) Anemone. Has characteristic deeply folded oral disc, with short tentacles. Often found attached to something solid while surrounded by sand in very shallow water. Come in browns, blue, green, pink, purple tentacle colors. Seen below are a specimen in Indonesia and a close-up in captivity.
Stichodactyla haddoni (Saville-Kent 1893), Haddon's (Carpet) Sea Anemone. Variably folded disc surface, open near surface. Has a tentacle-free central area. Very small tentacles. Lives in sand in which it can/does completely retract when disturbed. Close up and overall images of aquarium specimens.
Stichodactyla mertensii (Brandt 1835), Merten's (Carpet) Sea Anemone. Folded disc exceeding a meter in diameter in some specimens. Lives on hard surfaces that it covers closely. Small pedal disc, striated with some color. Short tentacles (1cm) of uniform color. Close up and further back on specimens in Pulau Redang, Malaysia shown below.

Naturally Symbiotic Relationships Between Amphiprionines and Actinarians (After Fautin)

#1 Cryptodendrum adhaesivum, #2 Entacmaea quadricolor, #3 Heteractis aurora, #4 Heteractis crispa #5 Heteractis magnifica, #6 Heteractis malu, #7 Macrodactyla doreensis, #8 Stichodactyla gigantea, #9 Stichodactyla haddoni, #10 Stichodactyla mertensii 

Other Anemones in the Hobby:

Condylactis species. Though most of these come to use from the tropical West Atlantic as inexpensive "Condys", there are Indo-Pacific species. This one in Fiji.

Environmental: Conditions

Anemones for the most part are extremely un-demanding. Some writers state otherwise, but many species have been maintained (and reproduced) in synthetic sea water. Many folks have suggested at least blending some natural with artificial marine water. Phillip Gosse in A Handbook to the Marine Aquarium in 1855 (yes, that's eighteen fifty-five), public aquaria, large trans-shippers, wholesalers, retailers, even I have had success in non-"real" water.

Habitat

Bellomy goes so far as to suggest a full-blown anemonarium. A suitable chemically inert glass or plastic container of as large a capacity as practical/available will help insure stability. Shallow water, intertidal species predictably make for good choices for small, crowded conditions.

Be aware of your species life habits, or at least be prepared to offer them a choice of light conditions, substrate types and variable circulation. See below re acclimation.

Chemical/Physical

Some writers list anemones as their choice for hardiest of marine animals, surviving/tolerating fluctuations in temperature, salinity and pH better than other groups. Many may be crowded together (some species of Condylactis) or housed in small aquaria. There are few things that seem fatal to anemones, other than metal-based chemical therapeutics or accidental introduction of metal ions from other sources.

For almost all species identified, absolute and varying specific gravity is not problematic. Keeping it between 1.022 and 1.028 is recommended. Ditto with temperature; something between seventy and eighty degrees F is great.

Keeping your eye on possible weak buffering by natural water, a pH of 7.6 to 8.3 is satisfactory. For crowded systems in particular, I would utilize a test kit weekly and periodically dose the system with water changes supplemented with a "pinch" of sodium bicarbonate or more-expensive adjuvant-equivalent.

Biology/Other

Anenomes are aerobes - they need oxygen to respire and need to shed themselves of excess carbon dioxide. Some have internal (endo)symbiotic algae (zooxanthellae) which aid in these processes, in addition to producing food sugars. Respiration is accomplished by simple osmosis and accelerated active-transport.

Filtration

Most importantly, circulation is important. I prefer a non-bubbly power-head, canister or inside-power filter over air-infusing mechanisms for moving the water around; but whatever the means do move it vigorously. One of my childhood heroes Robert P.L. (Straughan) warned against air-bubble entrapment mortality in captive anemones.

Good aquarium practices in set-up and maintenance will preclude anemone loss.

The removal of regurgitated food in mucus balls and bands through netting and siphoning must be a regular maintenance feature. Digestible foods are converted almost entirely into ammonia...to be removed by system filtration. Some filter-feeding anemones produce mucus nets, pass them up and over, trapping particles and ingest the whole mass. Mucus strands from locomotion and filter-feeding do not appear to be toxic.

Behaviour: Territoriality

What? Oh yes, they do can/move and do wage outright chemical/physical war with undesireable tankmates. In particular other stinging-celled organisms: corals, sea fans (gorgonaceans), and other anemones may sting/digest each other to the death. Suitable choice in specimens, crowding/provision of habitat are important considerations.

Introduction/Acclimatisation

First impressions are important! I stand by my advice; do not introduce the shipping/collecting water into the "home" system (unless possibly these are the only/first live specimens). Take the anemone(s) out of the shipping water, or alternatively rinse them over with holding system water, removing wastes and excess mucus. If possible do all this underwater including moving them into the system via a container. Place the specimens in their desired area, waiting a while for attachment if appropriate/possible. Overall circulation should be arrested for the meanwhile. Observe the new arrivals frequently for the first hours/day or so. Be careful when situating them near sharp corals, coral and shell skeletons or rocks. Purposely move them if necessary, otherwise they will move themselves.

Monacanthinids are not touchy in terms of handling stress. They typically "brighten up" shortly after introduction, displaying curiousity about their new digs.

Predator/Prey Relations

Can be important. Many fishes and crustaceans will eat anemones if hungry. Triggerfishes, puffers and many butterflyfishes are not to be trusted.

And yes, anemones may and do eat most anything they can snare. I wish you and I had all the money "spent" on feeding sea-horses, other barely mobile tankmates and unfamiliar species of fishes mixed with "exotic" anemones.

Reproduction:

Spans the entire gamut, sexual and asexual. New individuals may form from a piece torn off during locomotion or trauma, by longitudinal or transverse fission.

Sea anemones may be separate sexes or hermaphroditic. If same sex, generally eggs and sperm tend to be produced at different times. Fertilization and some development may occur within the body cavity or not. Typically, anemone larvae have a planktonic developmental phase before settling.

A gorgeous Heteractis magnifica Anemone in captivity undergoing asexual reproduction by bilateral fission.

Locomotion:

Is accomplished through a muscular-ciliary-mucus "gliding" of the bottom (basal or pedal disc) or complete loosening and "drifting" of the animal with current. Even mud-dwelling "tube" anemones are capable of moving and re-inserting themselves in soft substrates. Some species are actually pelagic, swimming about by lashing their tentacles.

Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes

Anemones possess rings of tentacles around their mouths used for prey collection and manipulation. These are arrayed with numerous stinging (cnidocysts) and sticky (spirocysts) cells below their surface. These specialized cells may be found in and on other body areas and assist in immobilizing and holding prey as well as warding off would-be predators.

Underfeed, underfeed, don't feed! Most losses in captive systems are the result of over-feeding. How many more times do I feel I need to write this? Bunches! Some anemones have been kept for YEARS without any intentional external feeding. Know your stock! Many anemones (especially larger species) are detritovorous (a polite term meaning they eat poop), planktivorous, and largely chemoautotrophic/photosyntheticizing species/individuals that hobbyists try to over-stuff with meaty/prepared foods. My bid for largest cause of loss of anemones is the consequences (lack of oxygen, hydrogen and other sulfide production...) from over-feeding. Cut it out! Within normal temperatures and other conditions, most can and do do well on weekly feedings. If you're going on vacation, leave them alone.

For almost all varieties kept, an occasional (weekly or so) perfusion (wash?) of live brine shrimp, prepared mash of frozen or dried food, or frappe (as in with your blender) of "fresh" marine food meant for human consumption (shellfish, shrimp, langusto, not-so-oily fish) with or without supplementation. Temporarily turn off your particulate filters and squirt the food onto their tentacular surface.

Some authors suggest the use of beef and other foods unlikely to be encountered in the wild. I do not.

Disease: Infectious, Parasitic, Nutritional, Genetic, Social

An unhealthy specimen is sometimes hard to discern. When acquiring, avoid flaccid choices over good turgidity. Good specimens should not be torn, leaking, with grayish, whitish necrotic or obviously infected areas. Photosynthetic species should show evidence (color) of yellow, golden or green symbiotic algae.

If a specimen shrinks down, don't automatically assume the worst and toss it. Maybe it's just "bummed-out" by too much/too little light, circulation, chewing tank-mates, polluted water from over-feeding, a metal source.

Bibliography/Further Reading:

Humann, Paul 1992. Reef Creature Identification, Florida, Caribbean, Bahamas. New World Publications, Inch. Jacksonville,Florida.320pp.