Barreleye

The Barreleye is a fish introduced in that appears in the Ocean. It can be found between 9 pm to 4 am all year.

Donating to the museum
Like all fish and insects in Animal Crossing, the Barreleye can be donated to the museum by talking to Blathers, the curator. He will tell the player some information about it when the player donates it.

In
When asked about the fish, Blathers will say the following:

"The barreleye is a deep-sea fish with protuberant eyes and a clear head, so some of its organs are... visible. At first blush, a transparent head seems absurd, but there is a reason: so it can see things directly above! But I must confess - the more I learn about deep-sea fish, the happier I am to live on dry land, wot."

The Barreleye can be found in the deep-sea fish tank at the very back of the aquarium.

Further Information
Macropinna microstoma is the only species of fish in the genus Macropinna, belonging to the Opisthoproctidae, the barreleye family. It is recognized for a highly unusual transparent, fluid-filled dome on its head, through which the lenses of its eyes can be seen. The eyes have a barrel shape and can be rotated to point either forward or straight up, looking through the fish's transparent dome.[1] M. microstoma has a tiny mouth and most of its body is covered with large scales. The fish normally hangs nearly motionless in the water, at a depth of about 600 metres (2,000 ft) to 800 metres (2,600 ft), using its large fins for stability and with its eyes directed upward. In the low light conditions it is assumed the fish detects prey by its silhouette. MBARI researchers Bruce Robison and Kim Reisenbichler observed that when prey such as small fish and jellyfish are spotted, the eyes rotate like binoculars, facing forward as it turns its body from a horizontal to a vertical position to feed. Robison speculates that M. microstoma steals food from siphonophores.[2]

M. microstoma has been known to science since 1939, but is not known to have been photographed alive until 2004. Old drawings do not show the transparent dome, as it is usually destroyed when brought up from the depths.