Monterey Bay Aquarium Research Institute scientists filmed a rare barreleye fish approximately 600 meters underwater offshore, marking their 11th encounter with the transparent-headed species and the first recorded in 4K resolution aboard their new research vessel, David Packard.
During an expedition aboard the research vessel David Packard, researchers from the Monterey Bay Aquarium Research Institute encountered a rarely seen barreleye fish, scientifically known as Macropinna microstoma. Researchers from MBARI’s Biodiversity and Biooptics Team were exploring waters filming and collecting deep-sea animals with the remotely operated vehicle Doc Ricketts when research specialist Shannon Johnson logged details of the sighting in MBARI’s annotation software.
Once news spread that the team had encountered a barreleye fish (Macropinna microstoma), it was standing room only in the ROV Doc Ricketts control room as the vehicle transmitted live footage from approximately 600 meters, or 1,970 feet, underwater, roughly 90 kilometers offshore.
Barreleye Fish Rotate Tubular Eyes Under Transparent Shield
The barreleye fish inhabits the ocean’s twilight zone, where it maintains a stationary drift using large fins for stability and maneuverability. Its large tubular eyes remain transfixed on the waters above, scanning for the silhouettes of prey. Once a potential meal is spotted, those eyes rotate beneath a protective dome of transparent tissue.
This gelatinous shield serves a dual purpose by protecting the animal’s eyes when it plucks small crustaceans caught in the stinging tentacles of deep-sea siphonophores. The expedition team spent roughly 20 minutes observing the fish, utilizing a high-resolution 4K camera on the Doc Ricketts alongside experimental lighting conditions to highlight the transparent head structure.
Macropinna reminds us of the surprising ways that animals have adapted to thrive in the ocean’s midwater.
Steven Haddock, senior scientist at MBARI
The scientific name Macropinna microstoma translates to large fins, small mouth,
features that were documented by Shannon Johnson using annotation software. ROV pilot and technician Cameron Law also maneuvered the vehicle close enough to record 3D stereo imagery using a VR camera to support future educational outreach.
Decades of Ocean Exploration and Rare Sightings
In nearly 40 years of ocean exploration, MBARI has completed approximately 7,000 ROV dives and accumulated over 41,000 hours of video. Despite this extensive effort, scientists have encountered Macropinna microstoma only 11 times, with the prior sighting occurring in 2021.
The Biodiversity and Biooptics Team studies how marine life interacts with light in dim depths. Researchers noted that the pigments in the lenses of the barreleye’s eyes likely function similarly to the green pigments found in the strawberry squid, another twilight-zone neighbor previously studied by the team. Although scientists did not collect the specimen during this expedition, the recorded footage provides resources for investigating visual adaptations against bioluminescent camouflage.
Earlier this summer, MBARI researchers collaborating with the Schmidt Ocean Institute in the mid-Atlantic Ocean documented another barreleye species known as the binocular fish (Winteria telescopa).