A School of Hawaiian Squirrelfish

A school of Hawaiian squirrelfish.
James Watt, USFWS Pacific

Check out the eyes on these Hawaiian squirrelfish (Sargocentron xantherythrum)! Because squirrelfish are almost entirely nocturnal, they need big eyes to absorb as much moonlight and starlight as they can in the dark. During the day, they hide out in the nooks and crannies of tropical coral reefs. To defend its small hiding place, the squirrelfish grunts by grinding its teeth and stretching the muscles along its gas bladders—grunts that sound a bit like the chatter of squirrels!