Rare Transparent-Headed Barreleye Fish Spotted During MBARI Expedition off California

MOSS LANDING, Calif. — Researchers with the Monterey Bay Aquarium Research Institute (MBARI) have reported a rare encounter with a deep-sea fish whose head is partly transparent, offering a glimpse of the remarkable life found far below the ocean’s surface.

The observation occurred October 20, 2026, during an expedition aboard MBARI’s research vessel David Packard. The fish, known scientifically as Macropinna microstoma or the barreleye, is so seldom seen that it marks only MBARI’s 11th documented encounter across nearly four decades of deep-sea research, according to an October 30 report citing the institute.

Why does the fish have a transparent head?

Barreleye fish have a fluid-filled, transparent dome around their eyes. The unusual structure helps scientists understand how these animals detect faint light and watch for prey in the deep ocean. Their tubular eyes can be directed to search for food above them.

This species typically lives around 1,500 to 2,600 feet below the surface, a realm too deep and dark for most casual marine observations. Even extensive scientific missions rarely see it.

A very rare sighting

MBARI has recorded more than 41,000 hours of deep-sea video over its history. The October 20 encounter was reportedly the first sighting of the species by the organization since 2021.

The observation highlights why locally based ocean research is valuable. Direct observations, camera systems and remotely operated vehicles enable scientists to document species that are otherwise difficult to study without disturbing their habitat.

What it means for Monterey Bay

The deep waters offshore of Monterey Bay make the region a globally significant center for marine science. MBARI, headquartered in Moss Landing, conducts research on ocean ecosystems and develops technologies to explore the deep sea.

Residents can explore the institute’s research and educational videos at mbari.org. This reported observation is a scientific encounter, not evidence that the fish is unusually abundant or easily seen near shore.

Illustrative photograph: NOAA / Unsplash, documenting other deep-sea research; not MBARI’s October 20 barreleye encounter.

Sources: Monterey County Now, October 30, 2026, reporting MBARI’s observation; Monterey Bay Aquarium Research Institute.

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