Author: Bethany Brookshire / Source: Science News for Students
Some fish really have a twinkle in their eyes. A small reef fish can aim light through its bulging eyes and onto a reflective surface to send a blue or red flash into the water.
The fish make more flashes when their favorite prey are present. These glimmers, which scientists call optical sparks, might therefore help the fish keep an eye on their potential meal.At the University of Tübingen in Germany, Nico Michiels studies how fish use light. He noticed that a fish called the black-faced blenny (Tripterygion delaisi) has a particular glow to its eye. These fish live in shallow waters in the Mediterranean Sea and Atlantic Ocean. They like hanging out in crevices, then launching themselves at the tiny crustaceans they eat.
In the process, their eyes sparkle (see video below). “It really attracts your attention,” Michiels says. “It’s like there’s something glittery on the [eyes’] surface.”
Making eerie eye sparks
How do these fish make their eyes flash? In the black-faced blenny, “the lens of the eye sticks out…to quite a large extent,” Michiels says. “It’s like a bowl on the eye.” As light filters down into the water, it hits this bulging lens. That lens focuses the light coming into it. Light that passes through the lens and into the retina lets the fish see.
But in black-faced blennies, the lens doesn’t focus all the light onto the retina. It aims some light below the retina, onto the iris. This is the colored part of the eye. There, light bounces off of a reflective spot and back out into the water.
The result is a tiny spark that seems to come out of the fish’s eye.“It’s not a strong reflection,” Michiels says. He notes it’s about as bright as the light you’d see reflecting off a piece of white paper in a dark room.
But it’s not white light. Instead, the black-faced blenny can make twinkles in blue or red. “The blue is very…
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