Sawfishes are active predators with a fearsome appearance to match. These relatives of sharks and rays are famous for their “saws,” long flattened snouts that bear spiky teeth-like projections on either side, giving the sawfish its name. The saw functions mainly as a multifunctional hunting and feeding tool: it can both sense and handle prey in the water column or near the bottom. This makes the sawfish’s saw unique, as elongated snouts in other fishes are known to either sense or handle prey, but not both.
Like sharks and rays, sawfishes use electrosensitive receptor cells in their skin to sense electric fields that are produced by all living organisms. This sensory ability can be especially helpful when hunting in murky or dimly lit waters. Electroreceptor cells are particularly numerous on the top and bottom of the sawfish’s saw. The sawfish can search for nearby live prey sitting atop or partially buried in sand by waving its saw above the substrate, much like a handheld metal detector. Once a prey item is found, the sawfish can use its saw to pin the prey down or reposition it before biting into it. The saw can also detect live prey in the water column. Once prey is encountered there, the sawfish thrashes its saw side to side, resulting in prey that’s knocked out, cut apart, or impaled.
Sawfishes live in freshwater and marine inshore waters, where they are critically endangered worldwide. For instance, numbers of smalltooth sawfish (Pristis pectinata) off the coast of Florida have dropped significantly due to declining estuary health and overfishing.
For a video of the sawfish’s saw in action, check out this ScienceShots article.Edit Summary
“…[J]uvenile freshwater sawfish Pristis microdon [now known as Pristis pristis] 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.” (Wueringer et al. 2012:R150)