MOSS LANDING, Calif. - Researchers at the Monterey Bay Aquarium Research Institute recently solved the decades old mystery: How could a fish with eyes that look up, eat with a mouth that faces forward?
The fish is called the "barrel-eye" fish. A new paper by MBARI researchers Bruce Robison and Kim Reisenbichler shows that the fish's unusual eyes can rotate within a transparent shield that covers the fish's head. This allows the barreleye to peer up at potential prey or focus forward to see what it is eating.
"Wow, this is a cool fish," Reisenbichler said when he first saw the barreleye. He says the barreleye can be found in the canyons of the Monterey Bay, some 2,000 to 2,600 feet deep. MBARI was able to capture images of the fish thanks to it's remotely operated vehicles.
According to MBARI'S research, barreleyes typically live near the depth where sunlight from the surface fades to complete blackness. They use their ultra-sensitive tubular eyes to search for the faint silhouettes of prey overhead.
After documenting and studying the barreleye's unique adaptations, Robison and Reisenbichler developed a working hypothesis about how this animal makes a living. Most of the time, the fish hangs motionless in the water, with its body in a horizontal position and its eyes looking upward. The green pigments in its eyes may filter out sunlight coming directly from the sea surface, helping the barreleye spot the bioluminescent glow of jellies or other animals directly overhead. When it spots prey (such as a drifting jelly), the fish rotates its eyes forward and swims upward, in feeding mode.
Reisenbichler says the unique fish's adaptation comes into it's best utility when attempting to "steal" food caught by a jelly and avoid it's stinging tentacles.
"Its a very elegant means of collecting food that it would be very hard to make a story of if you hadn't seen it," Reisenbichler said.
He adds the new research reveals greater insight into the marine life food chain, and shows just how delicate the balance can be.
"Its just filling in another small piece of our puzzle on how different animals can interact with one another."
Robison and Reisenbichler hope to do further research to find out if their discoveries about the barreleye also apply to other deep-sea fish with tubular eyes.
