Ben Sproul was standing on a shallow sandbar offshore near Kill Devil Hills, NC when a huge school of Jumping Mullet raced by. He managed to catch the short, exciting moment on video. 

And why are they jumping? They could be avoiding predators, but there are a few theories (and old answers) as to why and one includes their need to absorb more oxygen. From australianmuseum.net.au

The research of Hoese (1985) suggests that Sea Mullet use this second category of movements to fill the pharyngobranchial organ (an area at the back of the throat) with air.

The trapped air is believed to allow the fish to remain active in water of low oxygen concentration for about five minutes.

Several interesting lines of evidence support this theory. The number of jumps is correlated with the concentration of oxygen in the water. The less oxygen, the more jumps.

Secondly, Sea Mullet feed during the day often in bottom sediments that have low oxygen concentrations. Jumping occurs much more commonly during the day. Sea Mullet rarely jump at night.

via Science Dump.