Meeting Abstract
Suction feeding is the most common feeding mode in adult and larval fish. Yet our current understanding of its fluid mechanics shows that there is a lower size limit to suction feeders because suction is not effective in the creeping-flow regime. The smallest known suction feeders are members of the carnivorous plant genus Utricularia (bladderwort), which feed on zooplankton using underwater suction traps that are roughly 1 mm in size. We hypothesize that small suction feeders can escape the creeping-flow regime by completing their feeding strikes before viscous flow is fully developed. To test our hypothesis, we recorded the flow patterns generated by suction events at frame rates of up to 50,000 per second, and characterized the flow inside and outside the traps. We found that the fluid is accelerated at rates in excess of 45,000 m/s2 and reaches peak speed in excess of 4 m/s, ensuring that the flow is inviscid. We conclude that the short duration of the feeding strike (less than 1 millisecond) creates an effective inward jet. The flow is well described by inviscid flow models, showing that flow speed is limited only by the pressure inside the trap, and that the initial acceleration is determined by pressure and channel length of the trap.
