Filter-feeding fish tend to cruise around, letting water flow in their mouths and pass over special structures that pluck out tasty morsels, and flush filtered water from the gills. But anyone with a dishwasher knows filters tend to get clogged. How do fish keep theirs clean?
A model of those gill structures provides an answer. Tiny vortices, like mini-whirlpools, not only whisk solids off the filter surface, but concentrate particles smaller than the filter's pores to let them be captured too.
The findings, published in Nature Communications by biologist Laurie Sanderson and colleagues from the College of William and Mary in Williamsburg, Virginia, may be used in a range of industrial applications, such as beer and dairy production, where fluids are filtered.
To nut out how filter-feeding fish stay efficient, Sanderson and her team looked to structures called "gill arches" in the mouth of paddlefish and basking sharks. A series of bony loops that support the gills, gill arches sit either side of the pharynx.
So Sanderson 3-D printed gill arch models as backward-facing ribs in a cone shape, popped them in a tank and let water flow through them, emulating a real fish mouth.
When dye was added, they saw the gill arches channelled the water flow between the ribs into currents and vortices, helping concentrate small particles, and keeping the filter clear.
This "vortical cross-step filtration" can be extended to other filter feeders, from tadpoles to baleen whales.
They also suggest the work be used to desgin better filters for practical use.
So one day, your cold refreshing brew might be filtered through a fish-inspired device.
Belinda Smith is a science and technology journalist in Melbourne, Australia.
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