Choosing a Clownfish and a Sea Anemone

Which reef enthusiast hasn’t been intrigued by the strange relationship of the clownfish and the sea anemone? The anemone mercilessly entangles various small fish in its paralyzing grip, but spares the little colorful clownfish the same fate, allowing it to nestle safely among its stinging arms. When no danger’s lurking, the clownfish enjoys dancing and darting through the dense forest of the anemone’s long arms. Creating a home for such a couple in the saltwater aquarium is relatively easy do if you know a little bit about the habits and biology of this dynamic duo.

Scientists have determined that part of the clownfish’s immunity to the anemone is literally only skin deep. The anemone does not recognize the clownfish as an enemy because the clownfish has a slimy coating that is a close chemical match of the anemone’s. In human terms, one might say they smell alike. Bolting into the web of anemone arms when danger lurks, the clownfish is rescued from hungry predators.

Although the clownfish-anemone relationship is a fascinating one to observe, scientists still are unsure about the benefits the clownfish provides to its host. Most think that the clownfish brings activity within the anemone’s vicinity, and increases its chances for capturing food. Such a give-and-take relationship is called symbiosis. And, although this relationship in nature proves a necessary one, each can easily be kept on its own in a home aquarium, where food is abundant and predators are of no concern. Although purists will maintain that clownfish should only be kept with anemones, they are considered one of the best start-up fish for a new tank belonging to an enthusiastic novice marine aquarist.

The Amazing Clownfish

Clownfish get their name from their waddle-like swim and vivid colors, but one could also argue that they’re named for their almost comical gender relationships.

All clownfish are born as males. The dominant fish in the habitat, usually based on size, will eventually morph into a female and the second-dominant male becomes her mate. Should the female die, the most dominant male in the group, usually her former mate, transforms into a female, and the next dominant male becomes her new mate. Despite this gender-switching, these fish are relatively easy to breed.

Clownfish are in the family Pomacentridae and live exclusively in regions of the eastern Indian Ocean that are inhabited by anemones. Thus it is also known as an anemonefish. The most common aquarium clown is the orange-and-white striped Amphiprion ocellaris. Growing to about 3.5 inches in length in the wild, it usually doesn’t get much longer than 3 inches when in captivity.

Clownfish in the wild maintain small home territories, which makes them easy to keep in a smaller tank. Do not keep clowns with fish such as triggerfish that eat anemones. Keep only one in a small tank or, if you intend to introduce anemones, no more than a pair in a 30-gallon aquarium. You need at least one anemone per couple or the fish will fight over whose anemone it is. Like most marine species, they need a pH of between 8.2 to 8.6, water temperatures of between 74 and 78 degrees Fahrenheit, and a specific gravity of about 1.022-1.027. Clownfish are some of the least picky eaters among marine fish. They are omnivorous and will eat flake-food, algae, crustaceans or frozen worms.

The Astounding Anemone

Anemones require a little more attention than clownfish. They are natural relatives of corals, jellyfish and hydra; invertebrates that possess stinging cells called nematocysts. Anemones are sedentary bottom or reef dwellers, nestling onto a hard surface. Your tank should have such a surface, possibly a chunk of live rock, to which an anemone can anchor. The current in the tank shouldn’t be too strong.

Anemones have photosynthesizing organisms, called zooxanthellae, living in their tissues and so light requirements in the tank are high (2 to 5 watts per gallon of water for 12 to 14 hours per day, preferably with some blue spectrum provided by actinic light bulbs or higher-temperature metal halide lighting). The zooxanthellae also give anemones color. If an anemone is stressed it will eject them, turn white and shrink down until it dies.

Anemones require no special filtration or aeration and water quality requirements are essentially the same as that of their companion clowns, although it is recommended that nitrates be below 10 parts per million. They can be fed finely chopped frozen shrimp and other such foods by using a turkey baster to squirt the food close to their tentacles.

Although the natural companion to the common clownfish is the carpet anemone, they are difficult to care for and are becoming endangered in their natural reef environments. But clownfish will accept many kinds of anemones as hosts. The greatest success stories speak of saddle anemones and smaller to medium-sized species. Clownfish also accept bubble anemones, Heteractis dorensis, and the long-tentacled anemone, Macrodactyla dorensis, but they stay away from anemones in the genus Aiptasia as well as tube and curlique anemones.