Physicists Investigate How Hatchetfish Camouflage in the Deep Sea

The midwater region of the ocean is the largest habitat by volume in the world, making up 99 percent of Earth’s livable space. It’s home to a myriad of occupants, many of which have evolved peculiar abilities to allow them to survive.

“They spend their whole lives sort of suspended in the middle,” says Alison Sweeney, an assistant professor in the Department of Physics & Astronomy. “Because they live in this three dimensional void, they have to deal with being potentially visible from every angle. There’s literally nothing to hide behind and so they end up hiding within the light itself. The deep sea is a really amazing place to look for cool biological optics because so much of the ecology is driven by light.”

Hatchetfish, so named because the shape of their bodies resembles the blade of a hatchet, are one of the “classic-example weirdo fish denizens of the midwater.”

Because many deep-sea creatures hunt by looking up and seeing shadows or silhouettes, hatchetfish's large flat bodies keep them relatively well hidden. Their skin is somewhat metallic-looking, resembling the dull side of aluminum foil.

Hatchetfish also have a line of photophores on their belly that produce light, or bioluminescence. This is useful for when the fish are swimming in waters shallow enough for sunlight to dominate. By producing their own light with the same intensity as the faint sunlight coming from above, the hatchetfish make themselves invisible to predators.

Click here to read the full article.

Arts & Sciences News

Michael C. Horowitz Awarded Department of Defense Grant to Lead Team on Study of Autonomous Systems and AI

Michael C. Horowitz, Professor of Political Science, will oversee the study of autonomous systems and artificial intelligence.

View Article >
Earthquakes at the Nanoscale

In collaboration with Robert Carpick and David Goldsby, Tian, who graduated from Penn in 2017 with a doctorate in physics, recently published a paper in Physical Review Letters which attempts to tackle these devastating natural phenomena by investigating the laws of friction at the smallest possible scale, the nanoscale.

View Article >
Doris Wagner Named Robert I. Williams Term Professor

A leader in the fields of plant biology, chromatin modification, and epigenetics, Wagner’s research focuses on understanding at the molecular level the complex changes that occur when an organism switches developmental programs.

View Article >
Wrongful Convictions Reported for 6 Percent of Crimes

A study from Penn criminologists results in the first general estimate for the prison population as a whole.

View Article >
Race Has a Place in Human Genetics Research, Philosopher Argues

Penn philosopher Quayshawn Spencer says there is a racial classification that’s medically useful to reliably sample human genetic diversity.

View Article >
Exploring the Sounds of the Middle Ages

Assistant Professor of Music Mary Channen Caldwell's freshman seminar course, “Hearing (in) the Middle Ages,” explores a range of sounds heard throughout the medieval period, whether produced by people, instruments, bells, or animals.

View Article >