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Clownfish are small colorfully-striped fish often found hanging among the tentacles of sea anemones. Also known as anemonefish, most are bright orange with with white or back markings and have big eyes and a cute expression. Scientists recognize 28 species living in tropical and subtropical waters in Indian and western Pacific oceans. The are members of the colorful damselfish family.

James Prosek wrote in National Geographic, Clownfish get their name from the bold color strokes on their body (from rich purplish browns to bright oranges and reds and yellows), often divided by stark lines of white or black, quite like the face paint on a circus clown. Seeing clownfish darting among the tentacled folds of an anemone is like watching butterflies flitting around a flowering plant in a breeze-blown meadow — mesmerizing. [Source: James Prosek, National Geographic, January 2010]

Twenty-nine species of clownfish live among the reefs from East Africa to French Polynesia and from Japan to eastern Australia, with the greatest concentration of diversity on the north coast of New Guinea in the Bismarck Sea (where with a little luck and a competent guide you can see seven species on one reef). On a recent diving trip to Fiji, Gerald Allen — a research associate at the Western Australian Museum and the world's clownfish authority — discovered the 29th species, Amphiprion barberi. That brought his lifetime total to seven clownfish (and nearly 500 species of reef fish). "I still get a huge buzz when I find something new," Allen says. "Amphiprion barberi is a beautiful clown, orange and red like a blazing ember on the reef."

Clownfish form monogamous pairs and family units that occupy a single anemone and can change their sex. Often a dominant female will occupy an anemone with a mate of a different color. Young non-breeding individuals live close to monogamous pairs. When the dominant female dies the male changes color and become the a female and boss of the anemone and mates with another male. If a male dies or becomes a female, a lesser males will become sexually-active and take his place.

Some species of clownfish are specific to a certain area. One species, for example, is found only in waters off the Maldives and Sri Lanka. Another is found only around the Seychelles Islands. Clark’s anemonefish is the most widespread it is found in the Persian Gulf, across the India Ocean and Southeast Asia and as far north as India and as far south as Australia.

Websites and Resources: National Oceanic and Atmospheric Administration ; Smithsonian Oceans Portal ; Ocean World ; Woods Hole Oceanographic Institute ; Cousteau Society ; Montery Bay Aquarium

Websites and Resources on Fish and Marine Life: MarineBio ; Census of Marine Life ; Marine Life Images ; Marine Species Gallery

Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Wikipedia article Wikipedia ; Coral Reef Alliance ; Global Coral reef Alliance ; Coral Reef Pictures ; The Global Coral Reef Monitoring Network; the International Coral Reef Action Network.

Clownfish and Sea Anemones

Common clownfish
Clownfish hang around and are able to survive among the venomous tentacles of sea anemones. They are able to do this because the mucous on their skin is different from that found on the skin of most fish, which stimulates the discharge of toxins by sea anemones. If a clownfish strays from the anemone for too long it must establish immunity after returning through a series of brief encounters with the anemone’s stinging tentacles. Scientists are examining the mucous coating on clownfish that protects it from sea anemone toxins.

James Prosek wrote in National Geographic, “Among scientists and aquarists, clownfish are also known as anemonefish because they can't survive without a host anemone, whose stinging tentacles protect them and their developing eggs from intruders. Of the roughly thousand species of anemones, only ten host clownfish. It's still a mystery exactly how a clownfish avoids being stung by the anenome, but a layer of mucus — possibly developed by the clownfish after it first touches an anemone's tentacles — may afford protection. "It's a slime that inhibits the anemone from firing off its stinging cells," Allen says. "If you ever watch a new little anemonefish coming into an anemone, it makes these very tentative touches. They have to make contact to get this chemical process going." Thus shielded, the clownfish, in effect, becomes an extension of the anemone — another layer of defense against anemone-eating fish, such as the butterflyfish. What's good for the clownfish is good for the anemone, and vice versa. [Source: James Prosek, National Geographic, January 2010]

A dozen or more clownfish of the same species, from juveniles to mature adults up to six inches long, can occupy a single anenome. (Allen has seen as many as 30 on specimens of Sticho-dactyla haddoni.) Cruising around their anemone, they snag plankton, algae, and tiny creatures such as copepods, often hiding within the folds of their host to eat the larger food items. In the wild, where grouper or moray eels threaten, clownfish rarely live past seven to ten years, but in the safety of captivity they can go much longer. My neighbor keeps a spry 25-year-old, which used to bite my knuckles when I cleaned out his reef tank years ago as a kid.

Clownfish and Sea Anemone Relationship

False Clown Anemonefish
at Great Barrier Reef
James Prosek wrote in National Geographic, Clownfish spend their entire lives with their host anemone, rarely straying more than a few yards from it. They lay their eggs about twice a month on the nearest hard surface concealed by the fleshy base of the anemone, and they aggressively protect the developing embryos. Just after a clownfish hatches, it drifts near the surface for a week or two as a tiny, transparent larva. Then it metamorphoses into a miniature clownfish less than half an inch long that descends to the reef. If the young fish doesn't find an anemone and acclimatize to its new life within a day or two, it will die.

Clownfish may venture away from the anemone to feed on zooplankton but when threatened they quickly return to the safety of the tentacles. About 10 species of anemone are known to host clownfish. Some will accept various species of clownfish. Others are species specific. The same is true with clownfish. Some are associated with a single species of anemone while other chose different species to host them.

Often times a breeding pair or a half dozen clownfish will live among a single host anemone. When several fish live at a single host there is a definitive pecking order with the larger fish having dominance over the smaller ones. The breeding females lays here eggs at the base of the anemone and her mate watches over them until they hatch, when the larvae of the bony fish that emerge drift in the currents and search for hosts of their own.

Young clownfish approaching a sea anemone for the first time do so very carefully but once they are used to their environment they actively move around the poisonous tentacles with few worries. Sometimes the clownfish will even crawl among the tentacles when the anemone closes up at night.

Clownfish receive protection from predators from the sea anemone. In return for this protection and scraps of food provided by the anemone, the clownfish keep's the anemone clean and occasionally feeds on the small parasites that torment it. Clownfish may also help attract fish and other creatures the sea anemone can eat and scare off some fish such as butterflyfish that are not affected by sea anemone poison and eat their tentacles.

Clownfish Hierarchy and Sexual Behavior

James Prosek wrote in National Geographic, “Clownfish may or may not become sexually mature adults. A strict hierarchy exists among the occupants of each anemone, which hosts only one dominant pair at any time. The female is the largest in this "family," followed by the male and the adolescents. A mature pair assure their continued dominance by chasing the juveniles, causing stress and reduced energy for food foraging. "During courtship especially, there's a lot of chasing between the dominant pair," Allen says. The female occasionally reminds the male who's boss by nipping at his fins. [Source: James Prosek, National Geographic, January 2010]

Many reef fish have the ability to change from one sex to another. Most, such as wrasses and parrotfish, change from female to male. But the clownfish is one of the few known to change from male to female: If a dominant female dies, the dominant male will become the dominant female, and the largest remaining juvenile will assume the role of dominant male. No one has yet identified the hormones responsible for this sexual plasticity. "It's a really good adaptive strategy to make sure the species is perpetuated," Allen says. "There will always be a breeding pair at any given anemone."

Clownfish and the Popularity of Finding Nemo

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Allard's clownfish
The popularity of film “Finding Nemo“ — whose central character was a clownfish — increased the popularity of clownfish as aquarium fish and ironically led to widespread poaching of the fish. Clownfish are now raised in fish farms in the Bahamas and other places. The trick to raising clownfish is to make sure they have an enough anemones in their tank.

James Prosek wrote in National Geographic, “When Andrew Stanton set out to make an animated children's movie set in the ocean and faithful to "the real rules of nature," all he needed was the perfect fish for his main character. Combing through coffee table books on sea life, his eye landed on a photo of two fish peeking out of an anemone. "It was so arresting," Stanton says. "I had no idea what kind of fish they were, but I couldn't take my eyes off them." The image of fish in their natural hiding place perfectly captured the oceanic mystery he wanted to convey. "And as an entertainer, the fact that they were called clownfish — it was perfect. There's almost nothing more appealing than these little fish that want to play peekaboo with you." [Source: James Prosek, National Geographic, January 2010]

So a star was born. Finding Nemo, the Pixar movie Stanton wrote and directed, won the 2003 Academy Award for best animated feature and remains one of the highest grossing G-rated films of all time, taking in over $850 million to date. Nemo — a clownfish of the species Amphiprion percula — introduced millions of children around the world to a wondrous tropical ecosystem: the coral reef and its denizens.

The clownfish and the anemone — their relationship has captivated home aquarists since the 1970s, when improvements in the shipping of fish and in tank design and filtration caused a boom. But never before has a fish had a bigger boost than the clownfish in the wake of Finding Nemo (unlike the notoriety of a very large mechanical killer with teeth). At first, fear spread through the aquarium industry that the story line would cause a backlash: Nemo is captured and held in a tank in a dentist's office, and his father spends the rest of the time trying to rescue him. "I'm here to tell you the opposite happened," says Vince Rado of Oceans, Reefs and Aquariums (ORA), a hobby-fish hatchery and wholesaler in Fort Pierce, Florida, whose sales of A. ocellaris — a Nemo look-alike species — jumped by 25 percent. "Thank God for little Nemo!"

Stardom has been a mixed blessing for clownfish themselves. For years it has cost much less to catch and ship wild-caught clownfish than to raise the fish in captivity. Breeding them in tanks presents certain challenges — getting the larvae to feed, for one — and it takes at least eight months to grow them to marketable size.

But the economics of wild clownfish have been changing: Rising fuel costs have made shipping them more expensive, and populations have been declining. Overharvesting and invasive collection methods, such as the use of cyanide to stun and capture fish, are destroying reefs and their inhabitants. In the Philippines and Indonesia, for instance, clownfish have been severely depleted. Loss of clownfish leaves anemones exposed and vulnerable to predation. When reefs go bad, one of the first things to disappear is anemones — and their clownfish. "They're a really good indicator group," Allen says.

Besides spurring demand for clownfish, Finding Nemo helped fuel the explosion of websites and chat rooms devoted to raising reef fish in captivity. ORA breeds 13 clownfish species, as well as designer exotics such as the Picasso clown. Rado says he sells some 300,000 clownfish a year — "that's several hundred thousand that won't be taken from the wild." Despite the reef degradation Allen has witnessed during his 40-year career, he says that in some areas "there's incredible hope. Many reefs are almost pristine and very healthy." His focus now, as a consultant for Conservation International, is "to identify these areas and help with their preservation before it's too late."

Although the movie may have harmed native populations, Stanton's colorful little character also created a new group of nature lovers, eager to preserve clownfish and their reef homes. "I hope it increased awareness," Stanton says. "I know it's precarious out there."


Coral gobies
Gobies are generally small fish that are often found around coral reefs or in tidal pools. They make up the largest marine fish family. There are more than 2,000 different species worldwide. Among them is the crabeye goby which has fin markings called double eyespots that mimic huge eyes and are spaced at the same distance as the eyes of gobies that feed on fish that feed on gobies.

Some inch-long translucent gobies live and feed in the mantles of giant clams. Another kind leaps from tidal pool to tidal pool as the tide retreats. Somehow they know exactly where all the pools are and never miss. Apparently they make a mental map while tide is high and remember it when the tide is low.

The orange-colored goby, fish found off the shores of Japan, changes sex. When a group of females are placed together the largest one turns into male, fertilizes the eggs and guards them. When a large male is placed with a small male the small male becomes a female.

Another species of gobies found near Japan live in burrows built by bulldozer shrimp. The two sea creatures have a symbiotic relationship. The gobies alert the nearly blind shrimps to approaching dangers. The shrimps, in return build the burrows used by the gobies and keep them clean by bulldozing the sand in search of food.

One of most renowned experts on gobies is the Emperor Akihito of Japan. Much of his works has been devoted to distinguishing between the difficult-to-distinguish goby species through comparisons of minute details of the fish’s shoulder blades. Akihito spends a great deal of time looking at specimens under a microscope in his palace laboratory.

The Exyrias akihito is a species of goby named after the Emperor. A bottom feeder, it is 10 centimeters long a and has big bug eyes and orange speckles on its translucent body. Peter Miller, an emeritus professor at the University of Bristol, told the Times of London, “He has made a very useful contribution, and I’m not saying that because he’s the Emperor. I have referenced his papers myself. I doubt there are more than a dozen scientists in the world who can match his expertise.”


Birdmouth wrasse
Wrasses are a large family of small fish that are often found around reefs. They often start out as females and become males who vigorously defend territories. As small females grow they become large enough to defend their own territories. When the become big enough they change sex, fight off male rivals and mate with females who come to visit.

If a male leaves the group, a female changes her behavior in minutes. Her color changes in a day. Within a week she produces sperm instead of eggs. The dominant female controls sexual activity in her group. If she leaves and doesn't return her mate becomes the dominant female and a younger male become her mate.

Wrasses are very good at changing color. One species quickly changes from ripples of green on an orange background to mostly orange when it suddenly opens it mouth to warn off a rival or stall a predator. Male flasher wrasses flare out fins with bright blue markings that flash on and off.

Describing the mating of flasher wrasses, Les Kaufman wrote in National Geographic: “Males shoot neon blue stripes across their bodies and outstretched fins, creating miniature laser-light show. Spurred to passion by a male’s display of lights, a female rose in the water column with her chosen suitor and released an explosive burst of eggs to mix with his sperm. Job done, the male instantly went drab, and the consummated pair sped to get safety of the reef.”

Cleaner Wrasses

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small wrasse cleaning a
large Humphead wrasse
Cleaners wrasses are small slim fish, about three inches long, with blue and white stripes that play an important role in the reef community by feeding on parasites that feed on other fish. They also eat dead skin and mucus.

Some fish pull up to sections of reef inhabited with cleaning wrasses like cars pulling up to a car wash. The fish wait and line and when it is their turn the wrasse picks off parasites, fungus and pests. The wrasses also provide free medical service, munching on tasty parasites which congregate around a given fish's open wounds. Wrasse cleaning station are often manned by a group of female wrasses and one male. When the male dies one of the females turns into a male.

The wrasses clean squirrelfish, sea bass, butterflyfish, moray eels, parrot fish, scorpionfish, jacks, grouper and other predators much larger than themselves. The wrasses even clean divers feet and climb into the gills and mouths of sharks and clean their teeth. The grooming of algae and other marine growths by wrasses is believed to help manta rays fend off life-threatening infections.

The wrasses set up cleaning stations at well defined areas. Fish signal they are ready to be cleaned by assuming a relaxed pose with their fins erect. The fish line up for their turn. One scientist observed 300 fish get cleaned by a single wrasse at a single station in a six hour period.

Cleaners wrasses swim in the mouths and clean many creatures that could easily consume them as a meal. Barracuda have been observed swallowing wrasses after having their mouths cleaned. Studies have shown that the wrasses seem to distinguish hungry hosts from non-hungry ones by oscillating around the host to size it up. When a wrasse faces a hungry coral trout in an aquarium in an experiment at the University of Queensland the cleaner wrasse oscillate to the side and did not go near the trout’s mouth. Around a well-fed trout the wrasse oscillated less often.

Descriptions of Wrasse Cleaning Stations

Describing a cleaner wrasse at work on a grouper, David Attenborough wrote: The wrasse "dances in front of the new arrival with a bobbing motion. The grouper now hangs in the water, holding open its gill covers and mouth, often with its body tipped more vertically than horizontally, sometimes head-up. sometimes head-down, in a posture that signals its willingness to have its toilet attended to...The little wrasse swims in and fusses all over its client, trimming off pieces of dead skin, snipping away infestations of fungus, boldly venturing right into the huge jaws and coming out through the gaping gill covers."

Describing a Pacific cleaner wrasse in action, Douglass Faulkner, "Boldly he swims up to one of them and pops his head into its mouth. The squirrel fish appears to be swallowing him whole. But the four-inch daredevil backs out unscathed. Approaching each squirrelfish in turn, he nibbles at the flanks of one, at the gill covers of another. When the visitors swim away, the slim blue-and-black fish remains by his post on the coral reef."

See Manta Rays

Jawfish and Garden Eels

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The three-inch-long yellowhead jawfish lives in a 12-inch burrow that its digs for itself. When a predator comes around it dives into the burrow tail first. The fish lines its burrows with pebble walls and often get into fights with other jawfish over possession of pebbles.

Female jawfish place newly hatched young in their mouth to keep them protected for predators while allowing water to circulate and provide them with oxygen. When feeding the jawfish hides her young in a reef hole. Males also incubate eggs in their mouth. Some fasten an upside-down jellyfish to their back for camouflage and defense.

Gardens of eels resembling two-foot-high sea grass can be found in some parts of the world, with the most well-known ones in the Red Sea. These eels bury their tails in the sand in holes that are tightly sealed with mucous.

Colonies of garden can have thousands of members and the eel's mucus lined holes are sometimes only a few inches apart. Anchored to their holes the eels sway in the current eating sea squirts, fish eggs and tiny crustaceans that float by. Because they disappear quickly whenever a threatening object like a big fish, boat or a diver appears they were not discovered until the 1960s.

Image Sources: National Oceanic and Atmospheric Administration (NOAA); Wikimedia Commons

Text Sources: New York Times, Washington Post, Los Angeles Times, Daily Yomiuri, Times of London, Japan National Tourist Organization (JNTO), National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2012

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