A 'four-eyed' deep sea fish which uses powerful mirrors for eyes instead of lenses
A 'four-eyed' deep sea fish is the first to be discovered which uses powerful mirrors for eyes instead of lenses, say scientists. The spookfish, which lives at a depth of 3,280ft (1,000m), has been known to naturalists for 120 years, but the secret of its penetrating vision in the abyss had remained a mystery because no live specimen had been captured. Now, Professor Hans-Joachim Wagner, from Tuebingen University in Germany, has caught one off the Pacific island of Tonga. His research team used flash photography to confirm the fish's upward and downward gazes. Professor Julian Partridge, of Bristol University, who later conducted tests, confirmed it was the only vertebrate to have developed mirrors to focus the lights in his eyes in the murk where he lives. Prof Partridge said: 'In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes - how to make an image - using a mirror.' While the spookfish appears to have four eyes, it technically has two, each of which is split into two connected parts. Living at such depths, between Samoa and New Zealand, the spookfish needs one half to point upwards giving a view of the ocean and potential food above.
The other half, which looks like a bump on the side of the fish's head, points downwards. These 'diverticular' eyes are unique among all vertebrates in that they use a mirror to make the image. Prof Partridge said: 'Very little light penetrates beneath about 1000m of water and like many other deep-sea fish the spookfish is adapted to make the most of what little light there is. 'At these depths it is flashes of bioluminescent light from other animals that the spookfish are largely looking for. The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.' The mirror uses tiny plates, probably of guanine crystals, arranged into a multi-layer stack.
Prof Partridge made up a computer simulation showing that the precise orientation of the plates within the mirror's curved surface is perfect for focusing reflected light on to the fish's retina. He added: 'The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. 'That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.'
Spookfish Have World's Strangest Eyes 1
The four-eyed spookfish may have seemed strange enough. Now researchers say it doesn't really have four eyes. Instead, it is the known first vertebrate to use mirrors, rather than lenses, to focus light in its eyes. This is the only one known to have solved the fundamental optical problem faced by all eyes — how to make an image — using a mirror," said Julian Partridge from the University of Bristol. While the spookfish looks like it has four eyes, in fact it only has two, each of which is split into two connected parts. One half points upwards, giving the spookfish a view of the ocean — and potential food — above. The other half, which looks like a bump on the side of the fish's head, points down. These diverticular eyes, as they are called, are unique among all vertebrates in that they use a mirror to make the image, Partridge and colleagues found.
Very little light penetrates beneath about .62 miles (1,000 meters) of water. Like many other deep-sea fish, the spookfish is adapted to make the most of what little light there is. It is flashes of bioluminescent light from other animals that the spookfish are largely looking for. The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.
Although the spookfish was discovered 120 years ago, no one had discovered its reflective eyes until now because a live animal had never been caught.
When Professor Hans-Joachim Wagner from Tuebingen University caught a live specimen off the Pacific island of Tonga, members of his research team used flash photography to confirm the fish's upward and downward gazes.
Photographs looking down on the live fish produced eye-shine in the main tubular eyes that point upwards, but not in the diverticular eyes that point downward. Instead, these reflect light when seen from below.
It was when looking at sections of the eye that had been prepared for microscopy that Partridge realized that the diverticular mirrors where something exciting. The mirror uses tiny plates, probably of guanine crystals, arranged into a multi-layer stack. This is not unique in the animal kingdom (it's why silvery fish are silvery) but the arrangement and orientation of the guanine crystals is precisely controlled such that they direct the light to a focus.
A computer simulation showed that the precise orientation of the plates within the mirror's curved surface is perfect for focusing reflected light onto the fish's retina.
The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.
1. https://www.livescience.com/3191-spookfish-world-strangest-eyes.html
More from Creation.com :
Four-eyed spookfish has mirror eyes
Researchers Discover First Vertebrate with Eyes that Use Mirrors Rather than Lenses
A 'four-eyed' deep sea fish is the first to be discovered which uses powerful mirrors for eyes instead of lenses, say scientists. The spookfish, which lives at a depth of 3,280ft (1,000m), has been known to naturalists for 120 years, but the secret of its penetrating vision in the abyss had remained a mystery because no live specimen had been captured. Now, Professor Hans-Joachim Wagner, from Tuebingen University in Germany, has caught one off the Pacific island of Tonga. His research team used flash photography to confirm the fish's upward and downward gazes. Professor Julian Partridge, of Bristol University, who later conducted tests, confirmed it was the only vertebrate to have developed mirrors to focus the lights in his eyes in the murk where he lives. Prof Partridge said: 'In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes - how to make an image - using a mirror.' While the spookfish appears to have four eyes, it technically has two, each of which is split into two connected parts. Living at such depths, between Samoa and New Zealand, the spookfish needs one half to point upwards giving a view of the ocean and potential food above.
The other half, which looks like a bump on the side of the fish's head, points downwards. These 'diverticular' eyes are unique among all vertebrates in that they use a mirror to make the image. Prof Partridge said: 'Very little light penetrates beneath about 1000m of water and like many other deep-sea fish the spookfish is adapted to make the most of what little light there is. 'At these depths it is flashes of bioluminescent light from other animals that the spookfish are largely looking for. The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.' The mirror uses tiny plates, probably of guanine crystals, arranged into a multi-layer stack.
Prof Partridge made up a computer simulation showing that the precise orientation of the plates within the mirror's curved surface is perfect for focusing reflected light on to the fish's retina. He added: 'The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. 'That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.'
Spookfish Have World's Strangest Eyes 1
The four-eyed spookfish may have seemed strange enough. Now researchers say it doesn't really have four eyes. Instead, it is the known first vertebrate to use mirrors, rather than lenses, to focus light in its eyes. This is the only one known to have solved the fundamental optical problem faced by all eyes — how to make an image — using a mirror," said Julian Partridge from the University of Bristol. While the spookfish looks like it has four eyes, in fact it only has two, each of which is split into two connected parts. One half points upwards, giving the spookfish a view of the ocean — and potential food — above. The other half, which looks like a bump on the side of the fish's head, points down. These diverticular eyes, as they are called, are unique among all vertebrates in that they use a mirror to make the image, Partridge and colleagues found.
Very little light penetrates beneath about .62 miles (1,000 meters) of water. Like many other deep-sea fish, the spookfish is adapted to make the most of what little light there is. It is flashes of bioluminescent light from other animals that the spookfish are largely looking for. The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.
Although the spookfish was discovered 120 years ago, no one had discovered its reflective eyes until now because a live animal had never been caught.
When Professor Hans-Joachim Wagner from Tuebingen University caught a live specimen off the Pacific island of Tonga, members of his research team used flash photography to confirm the fish's upward and downward gazes.
Photographs looking down on the live fish produced eye-shine in the main tubular eyes that point upwards, but not in the diverticular eyes that point downward. Instead, these reflect light when seen from below.
It was when looking at sections of the eye that had been prepared for microscopy that Partridge realized that the diverticular mirrors where something exciting. The mirror uses tiny plates, probably of guanine crystals, arranged into a multi-layer stack. This is not unique in the animal kingdom (it's why silvery fish are silvery) but the arrangement and orientation of the guanine crystals is precisely controlled such that they direct the light to a focus.
A computer simulation showed that the precise orientation of the plates within the mirror's curved surface is perfect for focusing reflected light onto the fish's retina.
The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.
1. https://www.livescience.com/3191-spookfish-world-strangest-eyes.html
More from Creation.com :
Four-eyed spookfish has mirror eyes
Researchers Discover First Vertebrate with Eyes that Use Mirrors Rather than Lenses
