Frontiers of Science:

Clowning Around with Anemones

By Dr. Sherwood B. Idso

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    Can a clown fish from the Indian Ocean find happiness with an anemone from the Gulf of California? That is the question we asked ourselves as we watched our recently acquired Amphiprion bicinctus wriggle out of the plastic bag it had resided in for the past hour and into our aquarium. The salesman at the tropical fish store had assured us that the two of them would get along famously, but then that’s what he had also told us when we introduced a moray eel to our now seven-armed octopus!

    The meeting in this instance was considerably less dramatic. After hovering around in an upper corner of the tank for a few minutes and being sized up by the other fish, the banded clown made her maiden voyage across the ten-foot expanse of our upstairs show tank. Scattered across this stretch of sand and coral are twelve different anemones that we have collected from the Gulf of California just south of Puerto Penasco, Mexico. We wondered which one the clown would choose for her own. Would it be one of the smaller reddish ones? Or would it be the large brown and purple one in the center of the tank? Or maybe several of them?

    Throughout that first day we didn’t notice too much activity on the part of the clown fish directed toward any of the anemones. But then on the second day, we saw that she had taken up a semipermanent residence close by the large anemone near the center of the tank. And soon she was vigorously wriggling among the many tentacles of her newly claimed possession.

    This close association between clown fish and anemones has been a topic of some controversy among observers of the symbiotic (living together) relationship for several years. It has usually been agreed that nestled among the tentacles of the anemone the clown is protected from its enemies. But what does the anemone reap from the association?

    At various times it has been suggested that the clowns purposely provided anemones with food or even lured other fish toward the anemones’ grasping tentacles with their nematocysts (poisonous stingers). This view has been challenged, however, by the observation that although clown fish have been observed to bring large chunks of food to an anemone partner, they do not let the anemone eat it. Instead, they often tear at it as soon as the anemone has grasped it, feeding themselves with small portions they break away from the large chunk. In the end, the anemone is left with nothing.

    Which view is true? We decided to find out for ourselves—and find out we did.

    Our first step was to provide a suitable food source. A quick trip to a nearby pond supplied us with plenty of freshwater minnows. We introduced three of them to the tank. Immediately the water churned with activity as the community of marine fish began to subdivide the minnows for their lunch. But then, as if from out of nowhere, the banded clown darted into the melee and returned just as rapidly with one of the minnows intact in her mouth. The clown fish’s rapid wriggling reminded us all of the joyous wagging of a puppy’s tail as the puppy returns to its master with a stick it has retrieved.

    Upon reaching the large brown and purple anemone, the clown fish actually shoved the minnow down into its outstretched tentacles. Immediately they responded to the stimulus and began to close about the prey. Assured that the minnow was securely trapped, the clown turned back to the fracas at the end of the tank. Once again she somehow managed to secure another minnow, and once again she wigwagged her way back to the blob of bloated protoplasm (organized living matter) that comprised the plump anemone. Plumper still with her second delivery, the anemone was soon to be truly gorged when the clown returned a third time with the last of the minnows.

    On the following day, in the manner of true scientists, we proceeded to see if our observations were repeatable. And indeed they were. Not only did the clown fish again succeed in securing three minnows for the anemone, but she retrieved them when a sneaky Heniochus (pennant butterfly fish) stole them out of the anemone’s grip. And in no instance did the clown fish attempt to reclaim any of the minnows as her own.

    It thus appears that the answer to our initial query about the banded clown and the displaced anemone is affirmative. An A. bicinctus can indeed find happiness with an anemone from the Gulf of California, and the association is most certainly mutually beneficial. What else can you say about a friend who brings you a three-course meal each day?

    1 Two different types of anemones. The one on the left comes from the waters of Hawaii, while the one on the right comes from the Gulf of California in Mexico.

    2 The clown fish Amphiprion bicinctus just after it has delivered a minnow to the Gulf of California anemone.

    3 The clown fish delivers a second minnow to the anemone.

    4 A minnow being ingested by the Hawaiian anemone.

    5 Several other fish swim among the anemones, looking for food. At center is a Heniochus, while to the right is a sailfin tang and above is a blue tang.

    6 The anemones protect their food by completely engulfing it and withdrawing their tentacles.

    7 The Heniochus never gives up and comes in close to the anemone to steal any morsel he can find.

    8 He’ll probably be able to grab this minnow away from a baby anemone that is just not big enough to completely swallow it.

    9 After a hard day’s work, the clown fish rests peacefully among the tentacles of the anemone it fed the minnows to during the day.