Physics of fish


The Physics of Fish

Prof. James Puckett and Julia Giannini ’18 study collective animal behavior

“We know a lot about the atom, and about stars, but then somewhere in the middle of these two scales—life, basically—it gets messy,” explains Physics Prof. James Puckett.

Prof. Puckett and GianniniPuckett and Julia Giannini ’18, his research assistant, are sitting in their lab. At the back of the room is a small tank of rummy-nose tetra, a species of tropical fish that like their water around 26 °C (about 78 °F). To the left sits another large water tank Puckett and Giannini built by hand for their experiments, covered by a tarp to keep the warm water from turning the room into a sauna.

“If you don’t eat, your system will decay—that’s a normal, expected path your body would take,” continues Puckett. “But life always pushes things in different directions. Our everyday life is in an out-of-equilibrium state, which makes the physics of these systems very difficult to understand.”  In other words, getting back to Puckett’s original point… life is messy. 

Giannini and Puckett are working on a project to make sense of the messiness. Their research has two parts: the first is to observe how a school of fish behaves and reacts as an entity, and the second is to learn how each individual fish contributes to the group’s behavior.  They can then potentially apply these findings to other animals and species and make predictions about how they will behave and move as groups in different systems.

“This isn’t the whole story, it’s just a model. We know animals are way more complicated than this,” said Puckett.

But in general, all organisms behave in similar ways. Fish feel safety in numbers, as do humans. If someone gets too close and invades your personal space, you move away to reestablish a comfortable distance, as do fish. This behavior is not all that unlike the behavior of molecules in a system. For example, air molecules speed up and expand to fill a space as it gets hotter, and they slow down when it gets colder (which is why you may notice your tire pressure decrease in the winter). The cohesive forces of water molecules are responsible for surface tension.   Everywhere, we can observe the forces of attraction and repulsion at work. 

Investigating the practical applications of these principles is what first attracted Giannini to the project over the summer, when she started working with Puckett as part of the Cross-Disciplinary Science Institute at Gettysburg College. The Physics and Mathematics major said the interdisciplinary nature of the work was also a draw.


“As a first-year student studying physics, you learn about these concepts—Newton's Laws, forces, statistical mechanics—but it’s interesting to see them at play. I get to see all the moving parts behind this project,” Giannini said. “As a math major, you have computer science coursework, which I get to apply when I’m analyzing my data. Of course, underlying physical models is also a lot of math—and in this case biology, because we’re working with animals.”

In March, Giannini will present their preliminary findings at the American Physical Society meeting.

“Most people might think this is not really physics, what we’re studying,” said Giannini. “Part of this experience for me has been learning how to articulate why it is. I’m also learning the practical side of the work, like learning to solder, setting up the equipment on the computer, and I really appreciate that. It takes some of the mystery out of the science.”

Founded in 1832, Gettysburg College is a highly selective four-year residential college of liberal arts and sciences with a strong academic tradition. Alumni include Rhodes Scholars, a Nobel laureate, and other distinguished scholars. The college enrolls 2,600 undergraduate students and is located on a 200-acre campus adjacent to the Gettysburg National Military Park in Pennsylvania.

Contact: Carina Sitkus, senior assistant director of communications, 717.337.6803

Posted: Fri, 19 Feb 2016

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