Fish
Largetooth Sawfish
Pristis pristis · also called largetooth sawfish, freshwater sawfish, common sawfish
The largetooth sawfish is one of the strangest and most endangered large fish in the world — a several-metre ray whose snout has been drawn out into a flat, tooth-studded blade that works as both a sensor and a weapon. Sawfish once patrolled warm coasts and rivers on every tropical shore; today they are nearly gone.
Overview
The largetooth sawfish lives in shallow coastal water, estuaries, and rivers throughout the tropics, and it moves freely between salt and fresh water. It historically occurred in more than 90 countries across three oceans. It is a bottom-oriented predator, cruising over mud and sand flats and along mangrove edges, and it can tolerate very turbid, low-oxygen water that keeps other large predators out.
The saw
The rostrum — the saw — is an extension of the skull lined with 14 to 23 pairs of tooth-like denticles. Its surface carries dense electroreceptors that detect the electric fields of animals hidden in sediment or dark water, so the sawfish “sees” prey it cannot see. To feed, it swims into a school of fish and lashes the saw side to side, stunning and slicing several at once, then presses them to the bottom to swallow. The saw is not a weapon against people; injuries happen only to fishers handling a thrashing captured animal.
A ray in a shark’s body
For all its shark-like shape, the sawfish is a ray: its gill slits and mouth are on its underside, and its pectoral fins are fused to its head. It is most closely related to guitarfish and, more distantly, to stingrays and mantas.
River nurseries
Female largetooth sawfish give birth in river mouths, and the pups swim upstream to spend their first few years in fresh water, sometimes far inland — records exist from deep in the Amazon, the Zambezi, and Lake Nicaragua. This ties the species to the health of rivers as well as seas.
Status
The largetooth sawfish is Critically Endangered, and sawfishes as a group are considered the most imperilled family of marine fishes. The toothed rostrum snags in every kind of net, causing massive bycatch, and the animals have been targeted for fins, saws, meat, and oil. Combined with the loss and damming of their shallow-water and river habitats and their slow reproduction, this has erased them from most of their range. Northern Australia is the last place they remain reasonably secure, and they are now protected under national laws and international trade bans across much of the world.
Largetooth Sawfish: common questions
What does a sawfish use its saw for?
Two things. First, sensing — the underside and edges of the rostrum are covered in electroreceptors that pick up the faint electrical signals given off by the muscles and hearts of fish buried in sand or hidden in murky water, so the saw works as a metal detector for prey. Second, hunting — the sawfish swims into or alongside a school of fish and swipes the saw rapidly from side to side, stunning, cutting, or impaling several fish at once, then pins the prey against the bottom to eat it. The saw is not used to attack people and there is no record of an unprovoked sawfish killing a human, though a thrashing captured one can injure a fisher badly.
Is a sawfish a shark?
No, though it looks like one. Sawfish are rays. The giveaway is anatomy — a sawfish's gill slits are on the underside of its body, its mouth is underneath, and its pectoral fins are broad and fused to the sides of the head, all ray features, whereas sharks have gill slits on the sides. The confusion is understandable because the sawfish's body is long, muscular, and shark-shaped rather than the flat disc of a stingray or manta. The "sawshark" is a separate, smaller, genuinely shark group with barbels on its saw and side gills.
Why is the sawfish Critically Endangered?
The sawfish has been called the most threatened family of marine fish in the world. Its long, toothed rostrum tangles almost inevitably in any net — gillnets, trawls, seines — so it has enormous bycatch mortality, and it has also been deliberately caught for its fins (highly valued in shark-fin soup), its saw (sold as a curio and used in some rituals), its meat, and its liver oil. It lives in shallow coastal and river habitats that are heavily fished and heavily degraded, and it breeds slowly. It has vanished from most of the 90-plus countries it once inhabited; northern Australia now holds the last stronghold.
Do baby sawfish live in rivers?
Yes. The largetooth sawfish in particular is strongly tied to fresh water as a juvenile. Females give birth to litters of about 7 to 14 pups in estuaries and river mouths, and the young then move upstream and can spend three to four years living entirely in fresh water, sometimes hundreds of kilometres inland — historically they reached deep into the Amazon, the Zambezi, and Lake Nicaragua. This makes the species doubly vulnerable, exposed to both marine fishing and the damming, extraction, and pollution of rivers.