Monterey Bay Aquarium Research Institute (MBARI), Kalifornien, USA
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MBARI researchers Bruce Robison and Kim Reisenbichler used video footage from unmanned underwater robots, known as Remotely Operated Vehicles (ROVs), to study the so-called barrel-eyed fish in the deep waters off the coast of central California.
At depths of 600 to 800 meters below the surface, the ROVs' cameras showed these fish hanging motionless in the water, their eyes glowing a vivid green in the bright lights of the ROV. The ROV video also revealed a previously undescribed feature of these fish - the eyes are surrounded by a transparent, fluid-filled shield that covers the fish's head.
Researchers at the Monterey Bay Aquarium Research Institute recently solved the half-century-old mystery of a fish with tubular eyes and a transparent head. Since the first description of the "barreleye" fish Macropinna microstoma in 1939, marine biologists have known that its tubular eyes are very good at collecting light. However, it was believed that the eyes are fixed and only appear to allow "tunnel vision" of anything directly above the fish's head. A new paper by Bruce Robison and Kim Reisenbichler shows that these unusual eyes can rotate within a transparent shield that covers the fish's head. This allows the barrel eye to look up at potential prey or focus forward to see what it is eating.
Deep-sea fish have adapted to their pitch-black environment in a variety of amazing ways. Several species of deep-sea fish in the family Opisthoproctidae are called "barreleyes" because their eyes are tubular. Barreleyes typically live near the deep, where sunlight fades from the surface to complete blackness. They use their ultra-sensitive tubular eyes to search for the faint silhouettes of prey overhead.
In this picture you can see that although the shrimp's eye is pointed downwards, it is still looking straight up. This close-up
In this picture you can see that although the shrimp's eye is directed downwards, it is still looking straight upwards. This close-up "frame grab" from the video shows a barreleye that is about six inches (140 mm) long. Image: © 2004 MBARI
Although such tube eyes are very good at collecting light, they have a very narrow field of view. In addition, most marine biologists previously believed that the eyes of the tube eyes are fixed in the head so that they can only look upwards. This would make it impossible for the fish to see what is directly in front of them and it would be very difficult for them to catch prey with their small, pointed mouths.
Robison and Reisenbichler used video footage from MBARI's remotely operated vehicles (ROVs) to study the barleyfish in the deep waters off the coast of central California. At depths of 600 to 800 meters below the surface, the ROV cameras showed these fish hanging motionless in the water, their eyes glowing a vivid green in the bright lights of the ROV. The ROV video also showed a previously undescribed feature of these fish - the eyes are surrounded by a transparent, fluid-filled shield that covers the fish's head.
This front view of a Barreleye shows the transparent shield illuminated by the lights of MBARI's remotely operated vehicle Tiburon. As in the other photos, the two spots above the fish's mouth are olfactory organs called nostrils, which correspond to human nostrils. Image: © 2006 MBARI
This frontal view of a Barreleye shows its transparent shield illuminated by the lights of MBARI's remote-controlled vehicle Tiburon. As in the other photos, the two spots above the fish's mouth are olfactory organs called nostrils, which correspond to human nostrils. Image: © 2006 MBARI
Most existing descriptions and illustrations of this fish do not show its fluid-filled shield, probably because this fragile structure was destroyed when the fish were brought up from the deep in nets. However, Robison and Reisenbichler were very lucky - they were able to bring a netted barrel-eye to the surface alive, where it survived for several hours in an on-board aquarium. In this controlled environment, the researchers were able to confirm what they had seen in the ROV video: The fish turned its tubular eyes as it rotated its body from a horizontal to a vertical position.
In addition to their amazing "headgear", barleyfish have a variety of other interesting adaptations to life in the deep sea. Their large, flat fins allow them to remain almost motionless in the water and maneuver very precisely (similar to MBARI's ROVs). Their small mouths suggest that they can catch small prey very precisely and selectively. On the other hand, their digestive system is very large, suggesting that they can eat a variety of small drifting animals as well as jellies. In fact, the stomachs of the two fish caught in the net contained fragments of jellies.
After documenting and examining the unique adaptations of the Fassugen, Robison and Reisenbichler developed a working hypothesis about how this animal makes a living. The fish hangs motionless in the water most of the time, with its body in a horizontal position and its eyes facing upwards. The green pigments in its eyes can filter the sunlight coming directly from the sea surface and help the barrel-eye to detect the bioluminescent glow of jellies or other animals directly above it. When it detects prey (e.g. a floating jelly), the fish turns its eyes forward and swims upwards in feeding mode.
MBARI researchers speculate that Macropinna microstoma may eat animals caught in the tentacles of jellies, such as this siphonophore of the genus Apolemi
We would like to thank Kim Fulton-Bennett, Public Information Specialist from the Monterey Bay Aquarium Research Institute for the great photo!
Image: barreleye1.jpg
Credit: (c) 2004 MBARI
Description: The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that can rotate within a transparent, fluid-filled shield on its head.
The fish's tubular eyes are capped by bright green lenses. The eyes point upward (as shown here) when the fish is looking for food overhead.
They point forward when the fish is feeding. The two spots above the fish's mouth are olfactory organs called nares, which are analogous to human nostrils.
At depths of 600 to 800 meters below the surface, the ROVs' cameras showed these fish hanging motionless in the water, their eyes glowing a vivid green in the bright lights of the ROV. The ROV video also revealed a previously undescribed feature of these fish - the eyes are surrounded by a transparent, fluid-filled shield that covers the fish's head.
Researchers at the Monterey Bay Aquarium Research Institute recently solved the half-century-old mystery of a fish with tubular eyes and a transparent head. Since the first description of the "barreleye" fish Macropinna microstoma in 1939, marine biologists have known that its tubular eyes are very good at collecting light. However, it was believed that the eyes are fixed and only appear to allow "tunnel vision" of anything directly above the fish's head. A new paper by Bruce Robison and Kim Reisenbichler shows that these unusual eyes can rotate within a transparent shield that covers the fish's head. This allows the barrel eye to look up at potential prey or focus forward to see what it is eating.
Deep-sea fish have adapted to their pitch-black environment in a variety of amazing ways. Several species of deep-sea fish in the family Opisthoproctidae are called "barreleyes" because their eyes are tubular. Barreleyes typically live near the deep, where sunlight fades from the surface to complete blackness. They use their ultra-sensitive tubular eyes to search for the faint silhouettes of prey overhead.
In this picture you can see that although the shrimp's eye is pointed downwards, it is still looking straight up. This close-up
In this picture you can see that although the shrimp's eye is directed downwards, it is still looking straight upwards. This close-up "frame grab" from the video shows a barreleye that is about six inches (140 mm) long. Image: © 2004 MBARI
Although such tube eyes are very good at collecting light, they have a very narrow field of view. In addition, most marine biologists previously believed that the eyes of the tube eyes are fixed in the head so that they can only look upwards. This would make it impossible for the fish to see what is directly in front of them and it would be very difficult for them to catch prey with their small, pointed mouths.
Robison and Reisenbichler used video footage from MBARI's remotely operated vehicles (ROVs) to study the barleyfish in the deep waters off the coast of central California. At depths of 600 to 800 meters below the surface, the ROV cameras showed these fish hanging motionless in the water, their eyes glowing a vivid green in the bright lights of the ROV. The ROV video also showed a previously undescribed feature of these fish - the eyes are surrounded by a transparent, fluid-filled shield that covers the fish's head.
This front view of a Barreleye shows the transparent shield illuminated by the lights of MBARI's remotely operated vehicle Tiburon. As in the other photos, the two spots above the fish's mouth are olfactory organs called nostrils, which correspond to human nostrils. Image: © 2006 MBARI
This frontal view of a Barreleye shows its transparent shield illuminated by the lights of MBARI's remote-controlled vehicle Tiburon. As in the other photos, the two spots above the fish's mouth are olfactory organs called nostrils, which correspond to human nostrils. Image: © 2006 MBARI
Most existing descriptions and illustrations of this fish do not show its fluid-filled shield, probably because this fragile structure was destroyed when the fish were brought up from the deep in nets. However, Robison and Reisenbichler were very lucky - they were able to bring a netted barrel-eye to the surface alive, where it survived for several hours in an on-board aquarium. In this controlled environment, the researchers were able to confirm what they had seen in the ROV video: The fish turned its tubular eyes as it rotated its body from a horizontal to a vertical position.
In addition to their amazing "headgear", barleyfish have a variety of other interesting adaptations to life in the deep sea. Their large, flat fins allow them to remain almost motionless in the water and maneuver very precisely (similar to MBARI's ROVs). Their small mouths suggest that they can catch small prey very precisely and selectively. On the other hand, their digestive system is very large, suggesting that they can eat a variety of small drifting animals as well as jellies. In fact, the stomachs of the two fish caught in the net contained fragments of jellies.
After documenting and examining the unique adaptations of the Fassugen, Robison and Reisenbichler developed a working hypothesis about how this animal makes a living. The fish hangs motionless in the water most of the time, with its body in a horizontal position and its eyes facing upwards. The green pigments in its eyes can filter the sunlight coming directly from the sea surface and help the barrel-eye to detect the bioluminescent glow of jellies or other animals directly above it. When it detects prey (e.g. a floating jelly), the fish turns its eyes forward and swims upwards in feeding mode.
MBARI researchers speculate that Macropinna microstoma may eat animals caught in the tentacles of jellies, such as this siphonophore of the genus Apolemi
We would like to thank Kim Fulton-Bennett, Public Information Specialist from the Monterey Bay Aquarium Research Institute for the great photo!
Image: barreleye1.jpg
Credit: (c) 2004 MBARI
Description: The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that can rotate within a transparent, fluid-filled shield on its head.
The fish's tubular eyes are capped by bright green lenses. The eyes point upward (as shown here) when the fish is looking for food overhead.
They point forward when the fish is feeding. The two spots above the fish's mouth are olfactory organs called nares, which are analogous to human nostrils.
