The mechanics of fish evasion*

Fish evade predators by employing a rapid ‘fast C-start’ escape response. Previous studies of fish evasion focus on either identifying optimal evasion strategies, or on the mechanics of the fast C-start response. However, the connection between the mechanics of the fast start and the resulting evasion strategy is not well understood. Here, we develop a reduced-order mechanical model of the fast C-start, in order to evaluate the constraints imposed by the fluid-body mechanics on the evasion strategy. We employ a 3-link fish model and account for the fluid forces in the context of the potential flow theory. The model will serve to understand and evaluate evasion maneuvers in fish, it will also have implications for setting fast-start actuation in underwater soft robotics.