Ancient underwater giant

Education | Ocean Park 17 Sep 2019

The sawfish species in today's world appeared in the ocean around 56 million years ago.

The largetooth sawfish sports a flat head and a body that is grayish to golden brown, with gill slits and its mouth on its cream-colored underside. These predatory fish derive their name from the elongated, saw-like rostrum with 14 to 23 sharp teeth on each side. Males usually have two more on each side and like two rows of spears, the denticles are used for stunning or killing prey as well as self-defense.

Hailed as an ancient underwater giant, this bizarre-looking fish can weigh up to an astonishing 600 kilograms and grow to a length of 6.5 meters.

As an elasmobranch, a sub-class of cartilaginous fish which include sharks, rays, skates and sawfish, the largetooth sawfish is sometimes mistaken for a shark.

While the two share dorsal fins and similar swimming manner, the largetooth sawfish is in fact classified as a ray - with gills on their underside, while sharks have theirs on the side of the head.

Inhabiting the shallow waters of tropical and sub-tropical coasts and estuaries, sawfish are typically found chilling on muddy and sandy bottoms.

As a bottom-dweller, a largetooth sawfish feeds mostly on fishes, crustaceans and other invertebrates which it stirs up from the sea floor with its saw.

While its eyes are positioned at the top of its heads to ensure vision when it is on the sea floor, its tooth-lined saw has a special sixth sense for prey-hunting. Fine electromagnetic sensors called ampullae of Lorenzini along the largetooth sawfish's rostrum allows it to detect the weak electric waves given off by the muscle contractions of its prey, even in murky or dark waters. Once the prey is detected, the largetooth sawfish swipes its lethal rostrum to clash its prey before consuming it whole.

Largetooth sawfish are ovoviviparous animals, meaning the eggs hatch in the mother's uterus and are born live when fully developed. The mother normally gives live birth after five months to an average of seven to nine pups.

What is even more remarkable is that the rostra of sawfish embryos are protected by a membrane when inside the uterus to protect the mother from being injured during the pregnancy process.

Shortly after birth, the membrane dissolves so the young sawfish are ready for hunting small prey.

It is believed that the earliest species of sawfish first appeared 100 million years ago. Today's species have dwelled in the oceans for the last 56 million years. However, largetooth sawfish are approaching extinction due to fishing and habitat loss, and is now listed as Critically Endangered on the International Union for Conservation of Nature Red List.

People consume sawfish for their fins as "shark" fins (even though they are rays), use their livers for oil, skins for making leather, and eggs and bile as traditional medicine. Some are also illegally killed by people who want their unique rostra as souvenirs.

Though not often targeted nowadays, sawfish are still threatened by unintentional bycatch, illegal fishing and recreational fishing.Their long snouts make them particularly vulnerable to entanglement in fishing nets, including those discarded in the sea.

Apart from this, their estuarine and freshwater habitats are modified or destroyed by human activities such as agriculture, dredging, mining and alterations in water flow. Their life cycles - including slow growth rate and low number of offspring - means they are more susceptible to external threats. In the past decades, their population has declined.

We as individuals could also play a part in protecting the ancient warrior of the sea from extinction. This includes conserving their habitats, choosing sustainable seafood and saying a big "no" to eating the fins of sharks and rays.

To learn more, check out the largetooth sawfish at Ocean Park's Shark Mystique

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