Fish move not just by swimming but also by jumping, burrowing, walking, and flying. Many species though move by undulating their body and caudal fin (the tail fin that is used for propulsion). These body-caudal-fin (BCF) swimmers, as they are called, exert force against the surrounding water to support and move their body in an undulating motion. Traditionally, these fishes were classified based on key morphological traits and then grouped into four expected swimming modes based on four model species: eel, trout, mackerel, and tuna. But do all fish swim in certain ways based on this hypothesis?
Former and current members of Professor George Lauder’s lab determined to find out the answer. In their new study in Proceedings of the National Academy of Sciences the researchers showed that despite variability in body shape and native environments, there is convergence in the swimming motion across fish species.
The study, led by postdoctoral researcher Elsa Goerig and former postdoctoral researcher Valentina Di Santo (currently Assistant Professor at Stockholm University), performed a comparative study of 44 diverse species of BCF fishes. The researchers found that kinematics variables such as body oscillation amplitude and wavelength had little effect on the swim speed achieved by the fish during steady swimming. Combing both the fish morphology and the various kinematics they discovered that while fishes vary greatly in their morphology, the majority of species studied showed a similar suite of kinematic characteristics.
“We showed that fishes cannot be placed in discrete categories with regards to how they swim, but are rather located on a continuum,” Goerig said. “This highlights that despite variability in body shape and native environments, there is convergence in the swimming motion across species.”
Understanding how fish move can aid other fields including designing biomimetic robotic platforms and conservation applications, such as fish passage infrastructures, habitat restoration projects, and bycatch-reducing devices used in the fishing industry.
Study contributors also include former PhD candidate Dylan K. Wainwright (‘19, currently postdoctoral researcher at Yale University).