Deep-sea scientists have filmed an unusual fish that has a transparent head.
The barreleye fish (Macropinna microstoma) was caught on camera by Monterey Bay Aquarium Research Institute (MBARI) scientists during a recent expedition aboard the research vessel David Packard.
The fish lives in the ocean’s mesopelagic zone (or twilight zone) and is characterised by its gelatinous, translucent dome-like head. It’s the only animal known to have eyes inside its head, which allows it to scan the waters ahead and above in search of prey. This adaptation also provides the fish with a protective layer for when it plucks prey from the stinging tentacles of siphonophores (which are related to jellies).
Researchers from MBARI were exploring the farthest reaches of Monterey Canyon, at an MBARI research site approximately 90 kilometres (55 miles) off the Californian coast, when a member of the team saw the barreleye fish on the camera of the remotely operated vehicle Doc Ricketts.
“I’ve been lucky enough to see the barreleye a few times before, but my last encounter was nine years ago, before we had 4K cameras on the submersible,” says the expedition’s senior scientist Steven Haddock.
“It is such an amazing creature, which looks like it was created by an imaginative child. If you compare historical drawings of trawled specimens, the transparent dome surrounding their eyes has been stripped away. I didn’t even think they were illustrating the same species. So to see it alive with the dome of its ‘cockpit’ intact is a real privilege.”
The footage, which was captured in 4K, will help scientists to further understand how vision works in the darkness of the mesopelagic zone.
“Macropinna reminds us of the surprising ways that animals have adapted to thrive in the ocean’s midwater,” explains Haddock. “So many of them survive by looking for subtle optical cues, like a shadow passing overhead, and this sets off evolutionary competition, pitting bioluminescent camouflage against increasingly sophisticated visual capabilities.”
The barreleye fish was filmed on the eight-day Diving Deep for Delicate Drifters expedition, where MBARI scientists and collaborators aimed to study how gelatinous animals – such as jellies, siphonophores and ctenophores – have adapted to deep-sea conditions.
