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September 01, 2006

Are Marlins Lookdowns?

Maybe your Fish Facts experts can tell me why I always seem to see fish looking down!

Q: Maybe your Fish Facts experts can tell me why I always seem to see fish looking down! I've noticed this in artwork of big-game fish, as well as close-up photos of marlin, mahi and other species (fish with large eyes, so easy to see this). So my first question is: Am I crazy? Do these fish look down? Can they look up? I look forward to your assurance of my sanity.
Boris Von Ballavishny
Newark, New Jersey

A: Fishes such as marlins and tunas roll their eyes downward into their sockets in order to protect their delicate corneas, Boris. We consulted Guy Harvey and Kerstin Fritsches, biologists who have spent considerable amounts of time observing, studying and, in Dr. Harvey's case, painting the eyes of pelagic fishes. Both agree that this behavior helps protect these fishes' eyes. This is a well-documented behavior in white sharks, which, like marlins and tunas, lack nictitating membranes that would help protect their eyes. Interestingly, that behavior explains why, when being chummed to a boat, white sharks frequently turn away from their intended prey and bite metal objects instead. They roll their eyes for protection far down into their sockets, leaving them functionally blind when preparing to bite. At that point, white sharks rely on their electroreception capabilities rather than vision to home in on their prey during those final moments. A metal object immersed in saltwater puts out a stronger electrical signal than does a hunk of meat, so white sharks frequently end up biting shark cages, swim platforms and outboard motors. You mention noticing big-game-fish eyes aimed downward in artwork and close-up photos. That makes sense since these fish are often hooked and would be rolling their eyes downward to better     protect them from harm. - Ray Waldner