"Sailfish", National Geographic, September 2008
Sailfish (Istiophorus albicans) are the most prized sport fish in the world but very little is known about their behavior underwater. At 6 feet long, sailfish are the fastest swimming fish in the world. However, more than their speed, with this assignment we discovered that they are an exceptional predator and use their morphological design to catch their favorite prey, sardines. As they approach a school of fish they raise their sails to corral the bait ball, packing it tight. When their prey are confused and panicked they dive into the bait ball using their razor sharp bills to slice from side to side, wounding and isolating fish to prey on. Most amazing of all, they hunt as a group as do marine mammals, coordinating their efforts to collectively wear down the ball of sardines. They take turns driving the ball of sardines towards the surface and corraling them until the sardines are exhausted and finally succumb to the constant attacks.
Full article: http://ngm.nationalgeographic.com/2008/09/sailfish/holland-text