Scientists once assumed all filter-feeding fish used their mouths like colanders: Anything too big to fit through the holes stuck; the rest went out with the water. But Erin “Misty” Paig-Tran, a functional anatomist and assistant professor of biological science at Cal State Fullerton, wondered how that could be true. Filter-feeding manta rays and whale sharks she studied near Cancún, Mexico, fed in the same place at the same time, but ate totally different things.
By testing 3-D models of sharks and manta filters in the lab, she revealed how they do it. By adjusting their swimming speed and the width of their mouths or gill slits, the fish can catch their preferred food by manipulating the water flowing through their gullets. Generally, the faster the water’s speed, the smaller the food particles they ingest.