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Study Reveals Distinctive Filters of Rays

Manta, Devil Ray Research Could Be Used for Protective Measures

Oct. 18, 2013

Misty Paig-Tran, lecturer in biological science, is conducting research on the filters of manta rays and devil rays.

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Marine biologist Misty Paig-Tran marvels that some of the largest fish in the ocean, such as whale sharks and giant mantas, along with their smaller cousins, the devil rays, use filters in their mouths to capture and eat plankton.

To find out how they use these filters, Paig-Tran researched the anatomy of filters in manta and devil rays, discovering that each species has a uniquely identifiable filter to capture some of the smallest animals in the ocean, such as krill and zooplankton.

Her study findings recently were published as the cover article in the Journal of MorphologyThe Cal State Fullerton lecturer in biological science led the study, in collaboration with researchers at the University of Washington, where she earned her doctorate in biology last year.

"These rays use a mechanism called cross-flow filtration to capture their prey. Basically, this means particles hit the filter, and then are pushed to the esophagus. So it is a self-cleaning filter — and there is no clogging," said Paig-Tran.

For her research, the biologist filmed filter-feeding rays and whale sharks in the waters near the Yucatan Peninsula in Mexico, in order to examine their filter structures and placed satellite tags on some rays to monitor their feeding movements. She also trekked across the country to museums to examine the differences in filter-feeding fish specimens.

Paig-Tran's research focuses on biomechanics, or the blending of engineering and biology, to answer how organisms interact with the environment. Her study's findings have conservation and industry implications, as well.

Mantas and mobulas, including devil rays, are hunted because some people, mostly in Asian countries, believe the filters, when ground up and eaten, help to rid the human body of toxins.

"You can find hundreds of thousands of these filters stacked in markets in places like Indonesia, without the body of the ray," said Paig-Tran, adding there is no merit to these claims.

"To me, what was surprising, and most exciting about this study, is how we're able to identify which rays are being targeted for their filters, which will help conservationists, and how we protect them."

Her findings also may be valuable in developing innovative cross-flow filters for use in industry, such as in making soft drinks, wines and some pharmaceuticals.

Paig-Tran joined Cal State Fullerton in the spring to teach ichthyology — the study of fishes. She challenged her students to create short videos about their research topics, such as "Grunion Life History" by biology graduate student Ariel Carter and biological science major Elissa Lozano. 

This semester, she is teaching courses on human anatomy and physiology.

"The students here at Fullerton are pretty special. They work hard, they're dedicated and excited to learn about science," she said.

Paig-Tran earned her bachelor's degree in marine biology from Cal State Long Beach. She then studied biomechanics of filter-feeding fish at the University of Washington's Friday Harbor Laboratories, earning scholarly honors and securing grants for her doctoral research. In addition to teaching at CSUF, she is a postdoctoral research scholar at Arizona State University, studying the material properties and evolution of cartilage in deep-sea fishes.

Tags:  Academics & Research