You can’t put it much more succinctly than the excellent Deep Sea Research blog does: “Scientists Solve The Mystery Of Why This Fish Is So Freakin’ Crazy.”

The fish in question is the barrel-eye (Macropinna microstoma). The ‘freakin’ craziness’ is that is has upward pointing tubular eyes that can rotate inside its own transparent head.

Previously, researchers had apparently not realised that the eyes could rotate, leaving them scratching their own non-transparent heads as to why a fish would want eyes that could only look directly upwards, and are thus not very useful for getting food into their under-slung mouths.

They mystery was solved when Bruce Robison and Kim Reisenbichler used remotely operated vehicles from the Monterey Bay Aquarium Research Institute and observed that the fish could rotate its eyes. They also noticed the transparent head, which had been destroyed on previously described specimens (press release).

“The eyes are contained within a transparent shield that covers the top of the head and may provide protection for the eyes from the tentacles of cnidarians, one of the apparent sources of the food of Macropinna,” write the authors.

As Reisenbichler told Fox35, the fish will attempt to swipe food that has been caught by jellyfish, and the shield may stop them getting stung. “Its a very elegant means of collecting food that it would be very hard to make a story of if you hadn’t seen it,” he said.

The paper describing this work was published last year in Copeia. Videos are below the fold.

Image: © 2004 MBARI