The remarkable serrated snout attached to the face of sawfish has long fascinated ponderers of the piscine. Now a team of Australian researchers has figured out exactly how the animal uses its strange head ornament.
Similar beak-like protuberances on other animals are thought to be used to smack prey into submission or to detect the electric fields emitted by potential meals. Barbara Wueringer, a zoologist at the University of West Australia in Crawley, and her colleagues have discovered that sawfish (Pristis microdon) use their saws for both purposes, a first in the fish world, or indeed anywhere.
This is rather like using your nose to sniff out a freshly baked cake, and then using it to cut yourself a slice (a social faux pas if ever there was one).
Firstly the researchers checked that captured young sawfish did actually use their saws for fishing. When fed with mullet and chunks of tuna the animals were seen swiping at their dinner with their saws — as seen in the video below. “The movement can split a fish in half, impale it on the teeth or sweep it onto the substrate [of the tank],” they report in Current Biology.
But the animals — relatives of sharks — also seem to use their bills for sensing. Sawfish and related animals have a network of electro-receptors on their bills. In this new paper the team show that a weak electric dipole suspended in the water will elicit the same saw-waving behaviour used to feed.
And although they found no evidence that sawfish use their bills to root through sediment (actually they keep their snouts aloft when foraging on the bottom) another odd behaviour was observed. Sawfish were seen to scrape their teeth on the bottom at random points. Wueringer suggests that they could be sharpening them in preparation for their next use.
The authors point out that one of the reasons the fish’s numbers are declining is that their saws tend to get stuck in fishing nets. A better understanding of how the animals use these remarkable appendages could aid strategies to keep them free of entanglement, they suggest.
Image: Detail from a photo by Guy Incogneato via Flickr under creative commons.
Video: Courtesy of Current Biology and Dr. Barbara Wueringer.