Why the Sawfish Has a Saw

Few creatures are as alien to humans as those of the aquatic variety. They live in vastly different environments, after all. Humans breathe air; fish breathe water. Humans walk upright; fish swim horizontally.

And they don't come much more alien than the sawfish. And the tale of why they have such a strange appendage is no big fish story!

It is said that, when they first came into freshwater rivers from the sea - millennia ago - the sawfish didn't have the specialized snouts of today. Back then, they still bore long, but smooth, flat snouts; there weren't any of the sharp, toothy protrusions off the sides.

But the trouble with coming into the rivers from the oceans was the vegetation growing thick beneath the water; tangled roots in the mangroves made it difficult for larger fish to swim through to better breeding and feeding areas.

The larger fish taught their offspring to cut through the vegetation while they were small, so that sawfish of all sizes could swim up the rivers unhindered. As they grew and worked at the tough tree roots of the mangroves, their snouts became increasingly both hardened and jagged.

The more tree roots a snout cut, the more developed and pronounced the jagged protruding teeth became, and the more effective the rostrum was at the task. Before long, this became a most desirable trait to have in a mate for both sexes, as keeping their nests clear of debris was a very important task. The best mates had full, unbroken rostrums with long, developed cutting teeth sticking out fully sideways.

Natural selection did all the rest, and now the sawfish is a most efficient underwater deforester!

In some areas, the fish use their strange snouts not to cut tree roots, but to carve out shallow underwater caves to safely lay and protect their eggs!