This amazing underwater footage shows an aggregation of Sailfish, Istiophorus platypterus, feeding on a school of baitfish.
The scientific name Istiophorus platypterus literally means 'flat-winged sail bearer', in reference to the huge dorsal fin. The movie clearly shows the dorsal fin being raised and lowered during manoeuvring and while herding the baitfish.
Pepperell, J. 2010. Fishes of the Open Ocean. A natural history & illustrated guide. University of NSW Press. Pp. 266.