Saturday, August 20, 2005

Sawfish

Sawfish are related to sharks and rays. Their most striking appearance is a long, toothy snout. They possess a cartilaginous skeleton and no swim bladder. They are the sole family Pristidae of the order Pristiformes.
Their name comes from the Greek word "pristis", for 'saw'.
They are not to be confused with the sawshark, which is also in the order Chondrichthyes and bears a similar physical appearance.
The most eye-catching feature of the sawfish is of course, their saw-like snout; called a rostrum. The rostrum is covered with motion and electro-sensitive pores that allow sawfishes to detect movement and even heartbeats of buried prey in the ocean floor. The rostrum acts like a metal detector as the sawfish hovers over the bottom, looking for hidden food. It has also been used as a digging tool to unearth buried crustaceans. When a suitable prey swims by, the normally lethargic sawfish will spring from the bottom and slash at it furiously with its saw. This generally stuns or injures the prey sufficiently for the sawfish to devour it without much resistance. Sawfishes have also been known to defend themselves with their rostrum, against predators (like sharks) and intruding divers. The "teeth" protruding from the rostrum are not real teeth, but modified scales. Due to the appearance of the fish, sawfishes are sometimes called "Sharks with Swords".
The body and head of a sawfish is flat as they spend most of their time lying on the sea floor. Like rays, the sawfish's mouth and nares are located on its flat underside. The mouth is lined with small, dome-shaped teeth for eating small fish and crustaceans; though sometimes the fish swallows them whole. Sawfishes breathe with two spiracles just behind the eyes that draw water to the gills. The skin is covered with tiny dermal denticles (skin-teeth) that gives the fish a rough texture. Sawfishes are usually light grey or brown; the Australian Smalltooth Sawfish (Pristis pectinata) appears olive green.

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