Why do manta rays swim with their mouths open?

Manta rays feed by swimming through water with their mouths open and directing plankton, krill, and small fish into specialized filtering structures. Their gill rakers trap the food while water passes back out through the gills. This feeding method is efficient in nutrient-rich areas such as upwelling zones and reef channels. Unlike many fish that hunt individual prey, manta rays rely on dense clouds of small organisms. Their open-mouth swimming posture is therefore part of a highly specialized filter-feeding strategy.