April 11, 2016 — For years, when biologist Laurie Sanderson peered into the mouths of filter-feeding fish, what she saw was a puzzle.
How did such fish, from the foot-long menhaden to the 42-foot whale shark, manage to filter tiny food particles so naturally, so efficiently from the water flowing into their mouths and out again?
The answer wasn’t a simple dead-end sieve, like a coffee filter or colander, which ichthyologists assumed for centuries. In fact, Sanderson says, some textbooks still get that wrong.
No, what the professor at the College of William and Mary, her colleagues and students have teased out by studying the filter-feeding paddlefish and basking shark is that they have a complex mouth architecture — with a series of bone ridges or gill arches that have the marvelous ability to form vortices or eddies in the fluid flow. Those vortices serve to separate and collect tiny food bits before the filtered water is expelled.