by David Grant
Whether you do your fish-watching
in tropical seas or pet stores, one of the most interesting and
ubiquitous families of fishes is the Pomacentridae, or
demoiselles. The family is usually divided into three groups:
- the damselfishes, which off our southeast coast include the sergeant-major and the beau-gregory;
- the Pacific damsels of the genus Dascyllus;
- and the clownfishes, which are also confined to the Indo-Pacific.
As a family they also are some of the most entertaining fishes in the sea, and the most amusing of the three groups are the clownfishes.
There are twenty-six species in the clownfishes group. The most familiar of these belong to the genus Amphiprion; all of them boldly patterned in orange, red, white or black. Noted for their association with sea anemones, they are never found far from a host and flee to it when threatened. Not adapted to life in the open reef and helpless prey to larger fishes there, the clownfishes have come to rely on their relationship with coelenterates for survival. In fact, they are so dependent on these coelenterates that they are also commonly known as anemonefishes. The mechanism that the clownfish employs to avoid being stung by the anemone is not completely deciphered, but it is the classic example of symbiosis and one of the best examples of the complexity of the coral reef ecosystem.
There are a number of theories that account for the clownfishes' imperviousness to the anemone's stinging tentacles. Apparently the key is disguising yourself with mucous so the host anemone recognizes your skin as itself and doesn't discharge any stinging cells. In experiments where fishes that have had their mucous removed by detergents or scraping, they succumb to the stings.
Clownfishes are always busy and frequently seem to mouth, bite and even eat small bits of the tentacles. They may be removing microorganisms or feeding on slime. They even eat regurgitated food and excretions of the anemone. It's not apparent what benefit the anemone derives from this arrangement, although some have suggested the clownfish acts as a lure for prey for the anemone, or that it is purposely gathering food for it, or that the anemone may even utilize the fish's droppings. Regardless, it is a neat deal for the clownfish and fun to watch.
When confronted with a new anemone, clownfishes will approach it cautiously, teasing it with their tail until it opens. Apparently they are sensitive to its stings initially. The acclimatization process is fast though and soon a clownfish will chase away other fishes that are not part of its community on the host, and happily lounge about in the safety of its new home.
My first experience with clownfishes was as a proud owner of a pair of small specimens that I purchased along with a sea anemone. The three thrived together in an aquarium for over a year, giving me many opportunities to observe their behavior. Clowns are an especially appealing group of fish, having a pleasant neotonic look - like that wide-eyed and baby-faced expression Walt Disney used to make Mickey Mouse lose his rat-like appearance.
In the aquarium, clownfishes spend
most of their time frolicking in the tentacles of their "home"
anemone. They are distracted only by food, the approach of a
predator, or another clownfish, and I would expose them to a
mirror to watch their responses. Notoriously defensive when other
clownfish are near, they will bully others away from their anemone.
In captivity, they care for their anemone and bring food particles
within its grasp, although it is not clear whether they fret
as much over their host in the wild.
At night or when the anemone closes, the fishes hide deep within its tentacles, but apparently never become dinner; although the anemone's stings may help keep the clownfishes free of external parasites. It seems like a perfect relationship, at least for the clownfish.
Many years later I had the opportunity to work on the Red Sea and observe the clownfish in its own environment. The fringing reefs of the Sinai Desert are considered the finest in the world by many Europeans, and divers, anemones, and clownfishes are fairly abundant in its warm waters.
Because of the isolation of the gulf and high salinity waters here, the reefs harbor over 100 types of coral, quite a number of endemic reef creatures, and an outstanding assortment of fishes, including several species of clownfishes.
I was here working on an aquaculture project that allowed plenty of time for diving on the reefs adjacent to the lab. Occasionally we would assist each other on various projects, the "fishiest" being ongoing research by a behaviorist studying the similarities between clownfishes and damselfishes. He was comparing their aggressiveness in defending territory as a measure of how closely the various species of each group are related. In essence, letting the fishes communicate through their behavior, what the taxonomists could not do by measuring and comparing this similar-looking group.
Now, I couldn't enjoy watching fishes more if I were a cat, and it's always a toss-up as to who is more entertaining, animals or the researchers who study them; so it was never difficult to drag me along for some fish watching.
His project was a classical "gradual" school endeavor consisting of endless variations of the same theme: Find an anemone inhabited by a group of clownfishes; stay underwater until you are shivering uncontrollably and on the verge of hypothermia; observe the behavior of resident clownfishes when they are presented with various poorly constructed models of closely and distantly related clownfishes; determine which of the postures they made were defensive or submissive "displays"; compare how aggressively the fishes defended their "home" anemone from being usurped; and finally, conclude that you really only got decent observations at the very end of the dive and that it all had to be repeated again tomorrow.
It was soon apparent that while my associate knew plenty about behavioral psychology, he was weak in basic biology and not a very good model maker. I like simple solutions to problems and suggested trying mirrors or perhaps real fishes (Some might say all such research is "smoke and mirrors!").
Weeks later, things became a bit awkward when I arrived at work one morning to find live clownfishes sealed in plastic bags drifting in one of the holding tanks. The fishes were obviously stressed from lack of oxygen and some were resting on their sides, gasping for air.
I sought out my acquaintance, who quickly began telling me of his latest strategy involving live fishes. "I bag up clownfishes from one anemone and move them towards another anemone that is defended by more clownfishes; and I'm finally getting great results! Look at the display behavior!"
We discussed the responses he was observing as we headed towards the tanks and when we reached his captives I suggested that perhaps the lack of oxygen in the bags was affecting the fish's behavior. His reaction was memorable. As the implications of what I said began to sink in, his eyes focused on something that must have been miles behind me and his mouth dropped open like a two dollar suitcase. "Oxygen? Oxygen! Well ... I never considered that!"
Curiously, I was not invited on any other diving excursions, but I suspect that his research confirmed what many aquarists have discovered when they keep members of this group; that they are territorial and aggressive towards other fishes, particularly those that are closely related to them and might compete with them for food or space. And one should be mindful of these survival instincts when choosing aquarium mates.
My experiences underwater with fishes have always been interesting, but the most memorable were with the clownfishes near Eilat. Whether it is because they live in a stressed environment with fewer resources or simply that I had more exposure to them here, I found them to be feistier than any other little fish I've ever encountered.
Snorkeling over the shallow reef near the lab I regularly noticed larger clownfishes rising from their home anemone to inspect me. However, being new to the area and trying to absorb as much scenery as possible - as well as avoid fire coral, urchin spines and lionfishes - I didn't really focus my attention on these small inoffensive friends of the reef. Initially I assumed they were merely curious or were used to being fed by other divers, but I soon learned they were squaring off with me and defending their territory. When I came too close with my camera they would become visibly agitated and would charge it, behavior I'd seen before in Caribbean damsels.
I laugh when I think about how unaware we are of the world around us and it took several encounters with large clownfishes for me to realize what was happening with them. Or rather, what they were trying to tell me. One day I came across a particularly robust pair of fishes living in a large Stoichactis anemone on an isolated patch of reef. This would be the pair I would photograph for an entire roll of film on just clownfishes.
The fishes were cooperative ... too cooperative. As they swam out from their anemone to meet me I thought, "This will be easy." Apparently the larger clownfish had the same thought, but for different reasons. Squaring off in front of my face, it stubbornly blocked my path to the anemone and its companion. It was "Turk against Turk" over the reef in Eilat.
Clownfishes can move their eyes independently so they have a very expressive face. And if looks could kill, this fish was going about to do just that. At the same instant it finally dawned on me that all along these poor fishes had been reacting to their reflection in my camera lens and face mask and were defending their anemone, the clownfish decided it was about time to show this intruding member of its race just who had the hometown advantage. It charged head-on and rammed my mask! I'm not certain which of us was more flabbergasted.
Things look about one third larger underwater, and an angry fish that routinely chews on stinging anemones, even a small one, is not what I want hovering too close to my face. However, the fish had an expression like it had just banged heads with the "mother" of all clownfishes. We both returned to our comers eyeing each other warily until I retreated far enough that the clownfish felt secure and reciprocated by burying itself in the anemone and pouting.
Tucked away somewhere I still have my photo essay of clownfishes. Half the shots of a distant anemone with two tiny fish, the other half, a series of orange and white blurs of a clownfish that was too close and out of focus.
For the clownfish it was just another moment guarding the
old homestead and doing chores around the anemone. For me, it
was a day to remember. Another opportunity to learn from the
sea and a chance to commiserate with an endearing clownish.
Something to think about:
- What advantages are there to being "territorial" towards your own species as well as other species?
- How do clownfish avoid the stings of their home anemone?
- Define symbiosis.