Fluid Dynamics of Crossflow Filtration in Suspension-Feeding Fishes

College Of William And Mary, Williamsburg VA

Investigators

Abstract

This project will investigate the fluid dynamics of crossflow filtration in suspension-feeding fishes such as menhaden, anchovy, and carp. These fishes filter massive volumes of water to extract suspended food particles that are as small as 5 micrometer to 1 mm in diameter. Although they comprise approximately 25% of the world fish catch and have filtration efficiencies approaching those of industrial filters, the mechanisms that they use to trap their tiny prey remain largely unknown. A miniature fiberoptic endoscope has been used recently to observe particle movement inside the oral cavities of live suspension-feeding fishes. These data, combined with computational fluid dynamics simulations in fish oral cavities, have led to the development of a new model involving crossflow filtration in suspension-feeding fishes. Although crossflow filtration is a multi-billion dollar industry for the manufacture of products that we use every day (e.g., dairy products, beer and wine, pharmaceuticals), this filtration mechanism had not been recognized previously in any vertebrate. During crossflow filtration in fishes, particles are concentrated inside the oral cavity as filtrate exits between the gill rakers, but particles are not retained on the rakers. Instead, the high-velocity crossflow along the rakers carries particles away from the raker surfaces and transports the particles towards the esophagus. Equations from the industrial filtration engineering literature could be used to calculate the hydrodynamic forces on particles and the resulting particle velocities and trajectories during crossflow filtration in fishes. However, values that are appropriate for suspension-feeding fishes must be used in place of the variables in the equations. The empirical data needed for the first quantitative analysis of biological crossflow filtration will be provided by laboratory experiments involving sonomicrometry, pressure transduction, fiberoptic endoscopy, high-speed video, and flow velocity measurement with micro-thermistor probes. This analysis will provide insight into the process of crossflow filtration as it determines the sizes and densities of particles that suspension-feeding fishes retain. The study will engage undergraduate and Masters students in interdisciplinary research that has important ecological, evolutionary, and engineering implications.