This video says about itself:
Manta Rays Use Tiny Fish to Help Them Stay Clean
12 January 2018
Wrasse perform a vital cleaning function for other fish, by ridding their bodies of dead cells and parasites. Their biggest customers–literally and figuratively–are the massive manta rays. From the series: David Attenborough’s Great Barrier Reef: Visitors.
Manta rays have an unusual mouth filter that resists clogging. Instead of snagging in the filter, plankton ricochets toward the manta’s throat. By Laurel Hamers, 2:05pm, September 26, 2018.