How Do Fish Swim? Wellesley Biology Professor Looks for Answers in Lake Waban

December 5, 2018
A bluegill sunfish
Credit:
Clinton Moran

In the summer of 2016, a diver working with a research team headed by David Ellerby, associate professor of biological sciences at Wellesley, swam into Lake Waban and installed two underwater video cameras to record the movements of bluegill sunfish.

Ellerby, who studies physiology and the mechanics of animal locomotion, said this new technique has let him analyze fish swimming behavior in 3D detail.

Locomotion is a key factor in an animal’s fitness and ability to forage, reproduce, migrate, flee from predators, and adapt to changing environments. Researchers use bluegill sunfish as a model because of the abundance of lab data on this species’ swimming performance, energy use, and muscle properties.

“Previously, most of my work has been lab-based, with the focus on the physiology of movement in terms of energy cost and performance,” said Ellerby, whose study on the ecological relevance of swimming performance traits in bluegill sunfish recently appeared in Aquatic Ecology. “Our new goal is to make a better connection between lab data and the behavior of animals in their natural habitats.”

As a fish bends its body and flaps its fins against the current, researchers analyze the complicated interplay of fluid mechanics and biomechanics that propel a fish through the water, and they quantify parameters like body and fin motion, maximum speeds, and aerobic capabilities.

In the laboratory setting, fish swim in a tank in which water flow and speed can be regulated. In large tanks, researchers can recreate open-water environments found in a lake or in-shore spaces that are cluttered with submerged objects and underwater vegetation.

“You can measure behavior in a meaningful way in the lab, but you need the information from the lake to refine how you collect the data,” said Ellerby.

Ellerby didn’t have to leave campus to find an ideal setting for his field research. In Lake Waban, his team had the diver install mount underwater cameras in two distinct habitats—one just offshore, and the other farther out in deeper water.

In the video, Ellerby and his team observed that the fish in the various settings exhibited different behaviors: Those closer to the shore spent more time maneuvering slowly or hovering in one place as they foraged for food on submerged plants that grew on the bottom. Offshore, in open water, the fish moved faster and consumed plankton as they moved, and they interspersed periods of rapid tail beats with periods of nonpropulsive gliding.

Ellerby said the team will compare data from the field work with their analysis of lab experiments to “ensure that we’re measuring the right things in the lab in terms of patterns of movement, the energy costs of those patterns of movement, and how the swimming muscles actually power those movements.”

Photo: David Ellerby, associate professor of biological sciences at Wellesley, researched Lake Waban's bluegill sunfish, pictured here, as part of a case study for the ecological relevance of swimming performance traits in fish.