The freshwater sawfish
is a highly endangered species of fish that is trying to make a living in
rivers and estuaries, but many have been sent to aquarium prisons and others
are finding their habitat disappearing. They are related to sharks and rays and
like them and sturgeons they are sensitive to electric fields produced by fish.
The head of a sawfish has an elongated length
of cartilage, which has teeth sticking out along the length. A new study of these
creatures has just been published in Current Biology by Wueringer et al which describes how they use their
saw (1, 2).
The
saw has electric field detectors along its length which helps the fish find its
lunch, which may consist of catfish, mullet or freshwater prawns. But just as
many things in nature are dual or more purpose, so is the saw.
When
a nice juicy catfish is detected, a vicious sideways swipe impales the prey
fish and the sawfish then manipulates the fish to a head on position for
gulping down. Eating catfish whole this way is a must as it has poisonous
spines pointing backwards along its dorsal surface.
So
nature has provided the sawfish with combined lunch detector and weapon, which
is ever ready for action. It is readily sharpened by honing it on the bottom of
the river. The big downside is that nobody has taught it about fishing nets. A
fishing net full of wriggling fish can be too tempting and a quick slash at the
captured fish can end with the sawfish’s saw entangled.
- http://www.cell.com/current-biology/fulltext/S0960-9822(12)00085-1
- http://www.bbc.co.uk/news/science-environment-17258808
