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thomas712
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Just another interesting article I'd like to share with you all. Feel free to comment.
Clownfish Have a Nose for Perfume
Clownfish spend their entire life in a kind of marriage with their poisonous host, the sea anemone. But until recently it was not known how the tiny, juvenile fish could detect their many-tentacled host when first settling on a coral reef in the middle of the night.
Sea anemones are known to release powerful olfactory 'perfumes' which attract juvenile clownfish. While anemones are poisonous, clownfish are protected by mucus in their skin which lacks the compound necessary for the tentacles to 'fire'.
Michael Arvedlund, of James Cook University's Department of Marine Biology, has discovered that clownfish find their hosts by remembering their smell, which drifts over them as embryos. Having successfully raised clownfish in the laboratory for the first time, his theory was put to the test in the waters around Lizard Island and proved to be correct.
"Sea anemones survive by using their poisonous tentacles, with which they 'burn' and kill small fishes, and scare most potential predators away," he explained.
"Clownfish are the only exceptions. They guard their territory of anemones, and will heroically chase all enemies away, including butterfly fishes with their long trumpet-like mouths capable of biting off whole anemone tentacles. The clownfish's reward is their safety, living amongst colourful, protective tentacles which are instant death for most other little fishes."
Mr Arvedlund said it was not always easy to find clownfish on the Reef. More often than not it was the fish who, in an aggressive flurry, finds divers. Although not much bigger than your hand, it attacks fearlessly in defence of both its host anemone and its hidden nest.
Sea anemones have long been known to release very powerful olfactory compounds, which might best be described as perfumes.
"Nobody has been able to explain why this perfume is released, until hundreds of experiments conducted in the laboratory gave me the theoretical answer that the host sea anemone uses this tool to attract juvenile clownfish," he said.
An anemone's scent is imprinted on clownfish in their embryonic stage. Egg clutches, lying next to the anemone, are covered in its perfume-like compounds.
"My research indicated that clownfish become 'addicted' to the perfume as an embryo in the egg, lying next to the sea anemone covered in perfume-like compounds it releases. The theory then had to be proved underwater by locating a lot of clownfish egg-clutches nestled by host anemones."
Mr Arvedlund's research at Lizard Island confirmed that clownfish lay their shining red egg clutches right under sea anemones, so that the fish embryos were bathed in the flower's strong perfume.
And the evidence is plainly seen in an array of colourful slides of eggs, anemones and clownfish, photographed by his research photographer Dr Ingvar Bundgaard Jensen, who flew in to assist with field investigations.
"Over several weeks of successful dive investigations, I observed about 40 pairs of clownfish with egg-clutches and, without exception, they had all placed their clutch right next to their host anemone's column, not even a millimetre away."
By good memory, and a keen sense of smell, he said juvenile clownfish can quickly track down a suitable sea anemone by smelling their way to the perfume, when they settle on the reef two weeks later. Earlier American and Japanese research on the fate of reef fish larvae established that clownfish larvae emerge from the egg case after seven to nine days, and immediately swim to the surface.
"They swim around in the ocean, sometimes drifting with the currents, vulnerable to the environment, and feeding on plankton. After two weeks, the juvenile clownfish are about a centimetre long and ready to settle on the reef," he explained.
"This always happens in the middle of the night, when there is less chance of being discovered by a hungry predator."
Once the fish reach a coral reef, the search is on for a suitable host sea anemone to take them under its protective tentacles.
"Not all of them will be fortunate enough to find one, and the unlucky ones will end up on the menu of many larger fish or invertebrates on the reef. But for the lucky surviving ones, the smell they instinctively remember is their passport to safety."
Mr Arvedlund believes this chemical imprinting may be more widespread among reef fishes than is thought. He and a number of other scientists argue that smell is the trigger which leads most fish to coral reefs when they come to settle.
For example, a project funded by the Australian Research Council recently started by Australian researcher Dr Michael Kingsford of Sydney University and American Professor Jelle Atema of Boston is examining the role chemical cues play in encouraging fish larvae to establish their home territory.
"It is suspected that olfactory cues perhaps released from corals, similar to the perfume released from sea anemones, might be the trigger for many juvenile coral reef fish to settle," Mr Arvedlund said.
Meanwhile, the enigma of what makes the clownfish immune to the poisonous tentacles remains. While many theories have been published as the definitive answer, they are contradicted frequently by further research.
"Basically there are two main competing theories. I subscribe to the view of the late Dr Roger Lubbock from Oxford University, who thought that the mucus in the skin of the clownfish simply lacks the compound necessary for the anemone tentacles to 'fire'," Mr Arvedlund explained.
"The opposing theory, proposed by the German researcher Dr Dietrich Slicther, is that by rubbing themselves into the slime of the tentacles, the clownfish retrieves a protective shield against the stinging tentacles of the sea anemone.
"The mystery has intrigued researchers all over the world for almost a century, but the question still remains scientifically unresolved," Mr Arvedlund said.
Michael Arvedlund is a Danish Ph.D student in the Department of Marine Biology at James Cook University. This is an edited version of his submission to the CRC Reef Research Centre Ltd's 1998 Marine Science Journalism competition.
Clownfish Have a Nose for Perfume
Clownfish spend their entire life in a kind of marriage with their poisonous host, the sea anemone. But until recently it was not known how the tiny, juvenile fish could detect their many-tentacled host when first settling on a coral reef in the middle of the night.
Sea anemones are known to release powerful olfactory 'perfumes' which attract juvenile clownfish. While anemones are poisonous, clownfish are protected by mucus in their skin which lacks the compound necessary for the tentacles to 'fire'.
Michael Arvedlund, of James Cook University's Department of Marine Biology, has discovered that clownfish find their hosts by remembering their smell, which drifts over them as embryos. Having successfully raised clownfish in the laboratory for the first time, his theory was put to the test in the waters around Lizard Island and proved to be correct.
"Sea anemones survive by using their poisonous tentacles, with which they 'burn' and kill small fishes, and scare most potential predators away," he explained.
"Clownfish are the only exceptions. They guard their territory of anemones, and will heroically chase all enemies away, including butterfly fishes with their long trumpet-like mouths capable of biting off whole anemone tentacles. The clownfish's reward is their safety, living amongst colourful, protective tentacles which are instant death for most other little fishes."
Mr Arvedlund said it was not always easy to find clownfish on the Reef. More often than not it was the fish who, in an aggressive flurry, finds divers. Although not much bigger than your hand, it attacks fearlessly in defence of both its host anemone and its hidden nest.
Sea anemones have long been known to release very powerful olfactory compounds, which might best be described as perfumes.
"Nobody has been able to explain why this perfume is released, until hundreds of experiments conducted in the laboratory gave me the theoretical answer that the host sea anemone uses this tool to attract juvenile clownfish," he said.
An anemone's scent is imprinted on clownfish in their embryonic stage. Egg clutches, lying next to the anemone, are covered in its perfume-like compounds.
"My research indicated that clownfish become 'addicted' to the perfume as an embryo in the egg, lying next to the sea anemone covered in perfume-like compounds it releases. The theory then had to be proved underwater by locating a lot of clownfish egg-clutches nestled by host anemones."
Mr Arvedlund's research at Lizard Island confirmed that clownfish lay their shining red egg clutches right under sea anemones, so that the fish embryos were bathed in the flower's strong perfume.
And the evidence is plainly seen in an array of colourful slides of eggs, anemones and clownfish, photographed by his research photographer Dr Ingvar Bundgaard Jensen, who flew in to assist with field investigations.
"Over several weeks of successful dive investigations, I observed about 40 pairs of clownfish with egg-clutches and, without exception, they had all placed their clutch right next to their host anemone's column, not even a millimetre away."
By good memory, and a keen sense of smell, he said juvenile clownfish can quickly track down a suitable sea anemone by smelling their way to the perfume, when they settle on the reef two weeks later. Earlier American and Japanese research on the fate of reef fish larvae established that clownfish larvae emerge from the egg case after seven to nine days, and immediately swim to the surface.
"They swim around in the ocean, sometimes drifting with the currents, vulnerable to the environment, and feeding on plankton. After two weeks, the juvenile clownfish are about a centimetre long and ready to settle on the reef," he explained.
"This always happens in the middle of the night, when there is less chance of being discovered by a hungry predator."
Once the fish reach a coral reef, the search is on for a suitable host sea anemone to take them under its protective tentacles.
"Not all of them will be fortunate enough to find one, and the unlucky ones will end up on the menu of many larger fish or invertebrates on the reef. But for the lucky surviving ones, the smell they instinctively remember is their passport to safety."
Mr Arvedlund believes this chemical imprinting may be more widespread among reef fishes than is thought. He and a number of other scientists argue that smell is the trigger which leads most fish to coral reefs when they come to settle.
For example, a project funded by the Australian Research Council recently started by Australian researcher Dr Michael Kingsford of Sydney University and American Professor Jelle Atema of Boston is examining the role chemical cues play in encouraging fish larvae to establish their home territory.
"It is suspected that olfactory cues perhaps released from corals, similar to the perfume released from sea anemones, might be the trigger for many juvenile coral reef fish to settle," Mr Arvedlund said.
Meanwhile, the enigma of what makes the clownfish immune to the poisonous tentacles remains. While many theories have been published as the definitive answer, they are contradicted frequently by further research.
"Basically there are two main competing theories. I subscribe to the view of the late Dr Roger Lubbock from Oxford University, who thought that the mucus in the skin of the clownfish simply lacks the compound necessary for the anemone tentacles to 'fire'," Mr Arvedlund explained.
"The opposing theory, proposed by the German researcher Dr Dietrich Slicther, is that by rubbing themselves into the slime of the tentacles, the clownfish retrieves a protective shield against the stinging tentacles of the sea anemone.
"The mystery has intrigued researchers all over the world for almost a century, but the question still remains scientifically unresolved," Mr Arvedlund said.
Michael Arvedlund is a Danish Ph.D student in the Department of Marine Biology at James Cook University. This is an edited version of his submission to the CRC Reef Research Centre Ltd's 1998 Marine Science Journalism competition.
