Sawfish, freshwater

Pristis Microdon

phylum: Chordata

class: Elasmobranchii

order: Pristiformes

family: Pristidae

status: Endangered, IUCN

range: Australia, India, Indonesia, Papua New Guinea, South Africa, Thailand

Description and biology

Sawfishes are large rays (shark-like fish that live at the bottom of the water) with long, flat, tooth-studded rostra (snouts). The unique snout, usually between one-quarter and one-fifth of the sawfish's total length, is used as a weapon to kill or stun prey (usually small fish) or to fend off the sawfish's enemies when they attack. It is also used to forage in the muddy bottoms of the water for crabs or clams. The freshwater sawfish (also called the largetooth sawfish) is a medium-sized sawfish, but it is the largest freshwater fish in Australia. An adult freshwater sawfish measures about 9.8 to 23 feet (3 to 7 meters) and can weigh over 1,325 pounds (600 kilograms). It looks like a slender shark except for its distinctive rostrum, which holds 14 to 22 modified scales that look like teeth. It is dark yellow to gray in color and has a white or cream-colored underside. This coloring, common among fish, provides safety: if looking down on the fish from above, the dark color of its back will blend with the darkness of the water; if looking up from below,

the lightness of its underside will blend into the light from the surface. Freshwater sawfishes have wide, triangular pectoral (front) fins and tall, pointed dorsal (rear) fins. Sawfishes have breathing openings behind their eyes called spiracles, which are used to inhale water. Their eyesight is good, but in the dark water at the bottom of rivers they must rely more on other senses. Fortunately, their rostra are so sensitive that sawfishes can actually feel the heartbeat of their prey in the water. Freshwater sawfishes have the ability to travel from the sea into freshwater as they choose.

Freshwater sawfish probably mate every other year. They produce baby fish, rather than laying eggs as some other fish do. The female produces anywhere from 1 to 12 young (usually about 8) at a time. Pup sawfishes are around 2.5 feet (77 centimeters) long at birth. They are born with a protective covering over their saws, which are quite soft at the time of birth, probably to prevent injury to the mother. Their saws begin to harden quickly and the covering dissolves. They can begin to hunt small prey soon after birth. The freshwater sawfish reaches maturity at about 10 years of age and lives about 25 to 30 years.

Habitat and current distribution

The freshwater sawfish inhabits rivers, lakes, estuaries, and creeks. It moves between fresh and salt water easily, but probably prefers to sit on the bottom of shallow muddy rivers. It is not known to travel into the seas. Freshwater sawfish are found in fresh or brackish (part fresh water and part salt water) rivers in northern Australia, in Queensland, the Northern Territory, and Western Australia. They have been found up to 62 miles (100 kilometers) inland. The species has been known to range from southern Africa and eastern India through much of southeastern Asia to northern Australia, but appears to have disappeared from many regions where it once occurred. Australia may have some of the last healthy populations of freshwater sawfish.

History and conservation measures

All sawfish species are listed as endangered or critically endangered by the International Union for the Conservation of Nature and Natural Resources (IUCN). Some of the biggest dangers to the freshwater sawfish are gill nets and trawling nets. With their saws, these fish become hopelessly entangled in any net. Freshwater sawfish have also been hunted for their snouts, which are popular as souvenirs. Other parts of the fish's body have been used in traditional medicines. Over-fishing has depleted the fish. Habitat loss is also responsible for decline in the population.

The freshwater sawfish was listed as critically endangered in Australia under the Environment Protection and Biodiversity Conservation Act of 1999 (EPBC Act). In Australia, research was underway in the early 2000s to determine which waterways were occupied by freshwater sawfish. One of the problems in trying to protect this rare fish is that little is known about it. Australian conservationists (people who work to protect and manage nature and natural resources) have launched studies in order to acquire much-needed data about the species and its habitat needs.