A deep-sea fish species called the barreleye fish (Macropinna microstoma) has been observed with MBARI’s remotely operated vehicle (ROV) Ventana in Monterey Bay off California, the United States.
The barreleye fish (Macropinna microstoma). Image credit: MBARI.
Macropinna microstoma is a deep-sea ray-finned fish in the barreleye family Opisthoproctidae.
The species was discovered and described in 1939 by the U.S. marine biologist Wilbert McLeod Chapman.
It occurs at lower mesopelagic depths beneath temperate and subarctic waters of the North Pacific from the Bering Sea to Japan and Baja California, Mexico.
Macropinna microstoma measures around 15 cm (6 inches) in length.
It has a tiny mouth, most of its body is covered with large scales, and its eyes are capped with bright green lenses.
It also has a highly unusual transparent, fluid-filled shield on its head. This protects its sensitive eyes from the nematocysts (stinging cells) of the siphonophores, one of the apparent sources of its food.
“The barreleye lives in the ocean’s twilight zone, at depths of 600 to 800 m (2,000 to 2,600 feet),” MBARI scientists said.
“Its eyes look upwards to spot its favorite prey — usually small crustaceans trapped in the tentacles of siphonophores — from the shadows they cast in the faint shimmer of sunlight from above.”
“But how does this fish eat when its eyes point upward and its mouth points forward?”
“In 2019, our researchers learned the barreleye can rotate its eyes beneath that dome of transparent tissue.”
Macropinna microstoma normally hangs nearly motionless in the water using its large fins for stability.
Dr. Tommy Knowles and his team from the Monterey Bay Aquarium were aboard MBARI’s R/V Rachel Carson with ROV Ventana to collect jellies and comb jellies for the Aquarium’s upcoming Into the Deep exhibition when they spotted this fascinating fish.
“We stopped to marvel at Macropinna microstoma before it swam away,” the researchers said.
