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
"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."