The function of the sawfish's saw
Summary Jawed fishes that possess an elongated rostrum use it to either sense prey or to manipulate it, but not for both. The billfish rostrum, for instance, lacks any sensory function and is used to stun prey [1], while paddlefishes use their rostrum to detect and orient towards electric fields of plankton [2]. Sturgeons search through the substrate with their electroreceptive rostrum, and engulf prey by oral suction [2]. Here, we show that juvenile freshwater sawfish Pristis microdon are active predators that use their toothed rostrum — the saw — to both sense prey-simulating electric fields and capture prey. Prey encountered in the water column is attacked with lateral swipes of the saw that can stun and/or impale it. We compare sawfish to shovelnose rays, which share a common shovelnose ray-like ancestor [3] and lack a saw.