The most common theories as to why mullets jump out of the water are because the mullets are attempting to shake away parasites, break open eggs during spawning season or avoid predators. Mullets, also called gray mullets, are part of the Mugilidae family and are ray-finned fish found throughout the world in tropical and coastal waters.
Biologists speculate on the idea that mullet fish leap out of the water in order to clear water from the gills and increase exposure to higher levels of oxygen. This could be because the mullets spend a lot of time in waters that are low in dissolved oxygen. The Mugilidae family consists of 80 different species in 17 genera.