Abstract:
When suction-feeding vertebrates expand their buccal cavity to draw water into their mouth, they also exert a hydrodynamic force
on their prey. This force is key to strike success, directly countering forces exerted by escaping or clinging prey. While the ability
to produce high flow accelerations in front of the mouth is central to the predatorʼs ability to exert high forces on the prey, several
mechanisms can contribute to the disparity between the potential and realized performance through their effect on flow and
acceleration as experienced by the prey. In the present study, we test how interspecific variation in gape size, mouth
displacement speed and the fishʼs ability to locate prey at the optimal position affect variation in the force exerted on attached
prey. We directly measured these forces by allowing bluegill sunfish and largemouth bass to strike at ghost shrimp tethered to a
load cell that recorded force at 5000 Hz, while synchronously recording strikes with a 500 Hz video. Strike kinematics of
largemouth bass were slower than that of bluegill, as were estimated flow speeds and the force exerted on the prey. This
difference in force persisted after taking into account the faster suction flows and accelerations of bluegill, and was only
accounted for by considering interspecific differences in gape size, mouth displacement speed and fishʼs ability to locate the prey
at the optimal position. The contribution to interspecific differences in the force exerted on the prey was estimated to be 42% for
flow speed, 25% for strike efficiency, 3% for gape size and 30% for mouth displacement speed. Hence, kinematic diversity results
in substantial differences in suction performance, beyond those expected based on the capacity to generate a high flow velocity.
This functional complexity, in the form of biomechanically independent mechanisms that are recruited for one function, can
potentially mitigate performance trade-offs in suction-feeding fishes.