Thesis

Developing a mechanical model of a suction feeder

Suction feeding is a common feeding mode in macroscopic aquatic organisms and the dominant feeding mode in fish. In contrast, microscopic aquatic organisms do not use suction feeding. In fact, the smallest known suction feeders are fish larvae and bladderwort, a genus of carnivorous plants that catches zooplankton in underwater traps, both of which have gapes around 200 microns in diameter. Experimental and theoretical studies of suction feeding have shown that the ability to generate a steep spatial pressure gradient correlates strongly with capture success. Those studies also show that suction feeding is essentially an inertial process and therefore will be effective only if viscous fluid forces can be neglected, which is as long as the gape is large enough and the suction flow (i.e. the negative pressure gradient near the mouth) fast enough to minimize the relative effects of friction. Our current understanding of the hydrodynamics of suction feeding suggests that suction feeding is not effective in small organisms. In fact, both mathematical models of suction feeding, and experimental observations of larval fish suggest that their gape of 200 microns is near the lower size limit of suction feeding and that their suction flows generated by a 0.2 kPa pressure differential are too weak to ensure prey capture. In this project, we explored the lower size limit of suction feeding by characterizing the suction flows of bladderwort and salamanders and using the data collected to develop a robotic model of a suction feeder.

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