MBARI Films Barreleye Fish With Transparent Head in 4K for First Time

The Monterey Bay Aquarium Research Institute (MBARI) has recorded the first 4K footage of the barreleye, a deep-sea fish with a transparent head and upward-facing eyes. The video, released on October 28, shows the fish's green eyes clearly through its see-through skull.

The two dark spots above the mouth look like eyes, but they are actually the fish's nostrils. The real eyes are the green, tube-shaped structures inside the transparent head. They normally point straight up, scanning for the silhouettes of prey passing overhead.

How the eyes work

The eyes can also rotate forward. When the fish closes in on food, it swings them to look ahead and feed. MBARI described this mechanism in research published in 2009. The transparent dome covering the eyes also appears to protect them from the tentacles of siphonophores.

A rare encounter

The discovery was a matter of chance. Staff spotted the fish while the team was bringing the remotely operated vehicle Doc Ricketts back to the surface. Researchers and crew members then gathered in the control room one after another.

Over roughly 40 years, MBARI has sent its underwater vehicles down about 7,000 times and recorded more than 41,000 hours of deep-sea video. Even so, this was only its 11th barreleye sighting, and the previous one came in 2021.

The team observed the fish for about 20 minutes, adjusting the lighting while filming with a 4K camera. They also captured three-dimensional footage using a VR camera.

MBARI says the recording will be valuable for continuing research on the species. Close-up views of the eyes in particular could help explain how the fish sees in the dim waters of the deep sea.