Sawfish

From Encyclopedia Jr, free information reference for Kids

Sawfishes
Smalltooth sawfish, Pristis pectinata
Conservation status
Endangered (EN)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Chondrichthyes Subclass: Elasmobranchii Superorder: Batoidea Order: Pristiformes Family: Pristidae
Genera
Anoxypristis Pristis See text for species.

For other uses of the term, see Sawfish (disambiguation).

Sawfishes 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, from the Greek and Latin pristis meaning "sawfish" (cf. Greek πριστήρ pristēr meaning "saw").

They are not to be confused with sawsharks (order Pristiophoriformes), which have a similar physical appearance.

[edit] Physical characteristics

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 denticle scales (The scales of a sawfish have a similar structure to its teeth, confusing the distinction somewhat).

A plate sketching of a sawfish.

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 smalltooth sawfish, Pristis pectinata, appears olive green.

Like other elasmobranchs, sawfishes lack a swim bladder and use a large, oil-filled liver instead to keep them buoyant. Their skeleton is made of cartilage.

The eyes on a sawfish are undeveloped due to their muddy habitat. The rostrum is the main sensory device.

The intestines are shaped like a corkscrew, called a spiral-valve.

The smallest sawfish is the 1.4 m (4.6 foot) dwarf sawfish, Pristis clavata, a species much smaller than most other sawfish. The largest species seem to be the largetooth sawfish, Pristis microdon and the southern sawfish, Pristis perotteti, both of which can exceed 7 m (23 feet) in length. One southern sawfish, whose length for some reason went unmeasured, was said to have weighed 2,455 kg (5,400 lb).

[edit] Location and habitat

Sawfishes are found in tropical and sub-tropical areas around Africa and Australia and in the Caribbean, and frequently ascend far into rivers. They are also found in bays and estuaries.

Sawfishes live only in shallow, muddy water and can be found in both freshwater and saltwater. Most prefer river mouths and freshwater systems. All sawfishes have the ability to traverse between fresh and saltwater, and often do so.

[edit] Reproduction

Little is known about the reproduction habits of the sawfish. Each individual lives around 25 to 30 years, and matures at 10 years.

Females give live birth to pups, whose semi-hardened rostrum is covered with a rubbery envelope. This prevents the pup from injuring its mother during birth. The rubbery envelope eventually disintegrates and falls off.

The sawfish is estimated to mate once every two years, with an average litter of around eight pups.

[edit] Behavior

Sawfishes are nocturnal, usually sleeping during the day, hunting at night. Despite fearsome appearances, they are gentle fishes and will not attack humans unless provoked or surprised. The smalltooth sawfish is well known by fishermen as a prize game fish because of the fight it puts up once hooked. Capturing sawfishes is illegal in the United States and Australia.

[edit] Species

• Genus Anoxypristis
  • Knifetooth sawfish, Anoxypristis cuspidata (Latham, 1794).

    Also known as the narrow or pointed sawfish. Lives in muddy areas, appears grey.

• Genus Pristis
  • Dwarf sawfish, Pristis clavata Garman, 1906.

    Also known as the Queensland sawfish. Inhabits muddy bays and estuaries along the northern coast of Australia. Relatively small compared to other species, only around 1.4 m.

  • Largetooth sawfish, Pristis microdon Latham, 1794.

    Inhabits freshwater systems and have been found deep inland. The largest Australian freshwater fish.

  • Smalltooth sawfish, Pristis pectinata Latham, 1794.

    Also known as the wide sawfish. Lives in muddy areas, appears green or bluish-grey. Found Also lives in the Caribbean and around the Australian and African coastlines.

  • Large-tooth sawfish, Pristis perotteti Müller & Henle, 1841.

    Lives around the Caribbean and Central American coastline. Seriously endangered in Central and South America, especially Lake Nicaragua.

  • Common sawfish, Pristis pristis (Linnaeus, 1758).

    Once plentiful in the eastern Atlantic and Mediterranean, this species has become either critically endangered or is assumed extinct.

  • Longcomb sawfish, Pristis zijsron Bleeker, 1851.

    Prefers muddy bays and estuaries. The most common sawfish.

[edit] Conservation

All species of sawfish are considered endangered, or critically endangered. As well as being accidentally caught in fishing nets sawfish are also hunted for their rostrum (which is prized as a curiosity by some), their fins (which are eaten as a delicacy), their liver oil and for use as medicine.

It is illegal to capture Sawfish in the United States and in Australia. The sale of smalltooth sawfish rostra is also prohibited in the United States under the Endangered Species Act (ESA); the sale of other sawfish rostra remains legal however due to the fact that most rostra on the American market are from the smalltooth sawfish. Very few laymen can differentiate the species from which the rostra originated and it is therefore generally advised not to purchase sawfish rostra at all.

Loss of habitat is another threat to sawfish conservation.

Sawfishes are difficult to conserve in aquaria because it appears they may require a blend of saltwater and freshwater to stay healthy. However, the amount and duration of exposure are uncertain.

[edit] References

• "Pristidae". FishBase. Ed. Ranier Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.
• Sawfish - Sharks with swords
• Unique Australian Animals - Sawfish
• Photograph
• The Ocean Conservancy: Sawfish