Summary: Reef manta rays (Manta alfredi) have been observed feeding on fish gamete clouds produced during spawning aggregations (SPAGs) of three surgeonfish species (Acanthurus triostegus, A. guttatus, and A. lineatus) on Guam. This is the first documentation of such behaviour. Manta rays, being ram-filter feeders, consume zooplankton, and their presence was found to be positively correlated with the size of the surgeonfish aggregations. Spawning events occurred at specific times and depths, with larger events early in the year. The manta rays actively fed on gamete clouds during spawning, and both manta rays and surgeonfish departed after the process. This research provides important insights into the feeding behaviour of reef-associated manta rays and the predictable patterns of surgeonfish spawning on Guam.