Anemone keepers embrace several different feeding strategies; they vary based on species. Some feed anemones standard aquarium fare, such as cut fish or shrimp on a regular basis, while others refrain from feeding these tentacled pets any food at all, instead allowing the symbiotic algae living within the anemones to produce all of the creatures' nutrition. Anemones are a diverse group of animals whose diverse habitats require various feeding strategies. For best results, you should attempt to mimic your pets' diet in the wild.
Although they are similar to plants in many aspects, anemones are animals who dine -- at least in part -- on the flesh of other animals. Members of the phylum Cnidaria, anemones are close relatives of corals and jellyfish. Like their jellyfish relatives, anemones possess a collection of tentacles that contain specialized cells called nematocysts, which are capable of firing venom-tipped barbs into predators or prey. When an unsuspecting animal stumbles into the anemone’s forest of tentacles, the creature quickly succumbs to the venom. The anemone then draws the animal into its digestive cavity to complete the process.
Although all anemones share a few common characteristics, over 1,000 described species inhabit the world’s oceans. Across the group, anemones exhibit significant variation in their biology and natural history. While marine biologists understand some species rather well, others remain enigmatic. For example, crusty red anemones (Urticina columbiana) primarily consume jellyfish, whereas the fish-eating anemone, (Urticina piscivora) prefers its namesake prey. However, these and other cold-water anemones are not as common in the aquarium hobby as Indo-Pacific and Caribbean species are. According to marine biologist Dr. Ronald L. Shimek, tropical sea anemones' diet is not well established.
While captive anemones often consume fish, shrimp and other items when offered, many species also rely on alternative nutritional pathways. Like many corals, some anemones harbor tiny photosynthetic algae within their cells; these algae provide the anemones with sugars, while the anemones provide them with nutrients, carbon dioxide and protection. Such anemones require very well lit aquariums to thrive. Many species that harbor symbiotic algae require no supplemental feeding at all, although additional protein may accelerate growth or help trigger propagation.
If you keep an anemone who does not harbor symbiotic algae, supplemental feeding is required. Offer your anemone small bits of fish or shrimp, placing them near the oral cavity with a pair of long forceps. Different aquarists recommend various feeding schedules; some feed their captives three times a week, while others feed them only once every few weeks.
While anemones have stinging tentacles that immobilize their prey, some fish have evolved mechanisms by which they can pass through the tentacles without suffering harm. Accordingly, the fish can use the tentacles as a safe haven from predators. While the fish derive protection from the anemones, the anemones are able to consume scraps of food and waste from the fish. Various clownfish species commonly live amid the tentacles of different anemones, but cardinal fish (Pterapogon kauderni) and a few other species have evolved the ability to do so as well. Some invertebrates have also evolved the ability to live within the tentacles of an anemone.
Many aquarists keep clownfish and similar fish with their anemones. In such cases, supplemental feeding is likely unnecessary, as the clownfish waste and the food particles the fish create will feed the anemone. This is particularly true for those species with symbiotic algae.