Why does this fish have a "human face"? Watch it for three seconds and see who can hold back their laughter...

Without further ado, here are the pictures!

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Doesn’t it look like a “human face”? It has a mouth, eyes, and even two “thick eyebrows”.

But the part that looks like an eye is actually a nostril, and the part that looks like a mouth, eh! It really is a mouth, and this fish that looks so abstract is our protagonist today: the sawfish.

"Hold back your smile" Source: WWF

01

Shark? Or ray?

Sawfish are named for their serrated beaks. They belong to the pristidae family, a type of ray. Their scientific name comes from the Ancient Greek word πρίστης, which literally means "sawyer."

Their beaks are long and flat, an extension of the skull, made mainly of cartilage, covered with skin, and have teeth on the edges, making them look like a "saw".

Image source: Simon Fraser University

Generally speaking, the length of the beak is about one-quarter to one-third of the total length of the fish body. As the beak grows, the teeth on the saw will continue to grow over time. For example, the extra-large sharp teeth on the "saw" of the large-toothed sawfish look quite scary.

The white belly of the large-toothed sawfish, with two rows of gill slits under the pectoral fins

Image credit: J. Patrick Fischer

However, these are not real teeth, but dermal teeth specialized from the scales on the surface of the sawfish, so if the "teeth" on the saw are broken, they will not regenerate.

Compared with the common flat rays, the sawfish's body shape is actually more like a shark, and people often confuse it with the saw shark, which also has a "saw".

Saw shark Image credit: William Buelow Gould

From the outside

They do look alike.

But if you look closely you can quickly tell

Differences between sawfish and saw sharks:

First, look at the position of the gills. The gills of saw sharks are on the sides of the body, while the gills of sawfish are on the abdomen. Second, look at their "saws". The "saws" of saw sharks have a pair of whiskers, while the "saws" of sawfish have no whiskers.

Saw shark on the left and sawfish on the right

Image source: Wikipedia

In addition, they can be distinguished by size. Generally, saw sharks are relatively small, with a body length of about 1.5 meters. Sawfish are one of the largest fish in the ocean, with the largest species exceeding 7 meters in length. Even the smaller blunt sawfish is nearly 3 meters long, much larger than saw sharks.

But then again, there is a reason why sawfish and sawsharks look similar, because they are both cartilaginous fish, belonging to the group called elasmobranchs, and they have independently evolved serrated beaks through "convergent evolution."

In addition, sawfish have a very long history of existence. The earliest known sawfish fossil was discovered 60 million years ago, which is as old as sharks. Some scholars even speculate that they have a common ancestor with sharks.

Mask with sawfish beak Source: Wikipedia

For a long time, the classification of sawfish species has been rather confusing. It is now widely accepted that there are two genera and five species under the family Sawfish: largetooth sawfish, smalltooth sawfish, green sawfish, Queensland sawfish and blunt sawfish.

02

The "chainsaw maniac" in the sea?

In many literary works or folk myths and legends, sawfish are often described as terrifying sea monsters that not only attack large marine mammals such as whales and dolphins, but also attack ships and cut people in half.

"Sea Monster" Sawfish Source: Florida Museum

But according to research from the International Sawfish Encounter Database, there are actually no reliable records of sawfish behaving in this way. Generally speaking, sawfish are relatively docile and harmless to humans. Moreover, creatures such as whales and humans are too large to be within the hunting range of sawfish.

Of course, the premise is that humans do not capture them, because when encountering danger, sawfish will still wave their saws in self-defense, which will not only hurt people but also themselves.

So, what do sawfish like to eat?

In fact, sawfish is a kind of "bottom-dwelling fish". When they are young, they like to stay in the mangroves in shallow water areas. As they grow bigger, they will move to deeper waters. Therefore, their food is mostly crustaceans, cephalopods and other animals, as well as a few gregarious bony fish.

Image source: woggle

Like other cartilaginous fish, sawfish have electroreceptive abilities, which allow them to detect and track the movements of other organisms by measuring the electric fields they emit. But the difference is that sawfish have thousands of electroreceptors, the ampulla of Lorenz, all over their heads and beaks, which allow them to "see" their entire surroundings from the bottom of the ocean using an extended sensory system on their saws, with a range of up to 40 cm.

Even in waters with very low visibility, it does not affect sawfish hunting.

After finding their prey, what do sawfish do? The first thing that comes to mind is their "saw". That's right, this big "saw" is not just for intimidation, it's also a deadly weapon.

The sawfish is hunting. When its prey is far from the seabed, the sawfish will raise its head and use its beak to approach the prey, then quickly attack left and right, catching the prey off guard and forcing it to the seabed to be eaten.

Source: Screenshot of the paper video

The second scenario is that the prey is near the seabed, which happens to be the sawfish's comfort zone. When they find the prey, they will rush up quickly, and then quickly attack left and right until they press the prey with their beak and eat it. However, sometimes they will accidentally saw the prey in half.

Reverse, suppress, and eat a dragon. Source: Screenshot of the video in the paper

It is worth mentioning that no matter which method is used, the ultimate goal of the sawfish is to pin its prey to the bottom of the sea and then adjust its mouth position, trying to start eating from the head of the prey to avoid being "dorsal spines" by the fins.

03

Reproduction and the future

For sawfish, they need to prevent "backstabs" not only when eating, but also when reproducing.

Because sawfish are ovoviviparous, the young will fully develop inside the mother's body before being born from the uterus. This also means that the young will grow a beak with serrations inside the mother's body. If there is no way to avoid the damage caused by the serrations, then for every young sawfish born, a mother will die.

Obviously, nature is not capable of evolving such abstract stories.

During the mother sawfish's gestation period, a sheath grows inside the embryo and covers the newly grown teeth of the sawfish pup, thus preventing the teeth from causing damage to the embryo and the mother.

Researchers show sawfish calves with

Wrapped in a skin-like protective film

Image source: sciencenews

Some researchers have described the texture of this sheath: hard, slightly elastic, like paraffin, and basically difficult to peel off by external force. From the combined results of scanning electron microscopy and sample element analysis, the composition of this sheath includes keratin, reticular protein and collagen, which is simply a second layer of skin.

Within about four days after the cubs are born

The sheath will gradually die and fall off

Sawfish

It's really starting to show its fangs.

Image source: discover wildlife

As a large fish, sawfish is undoubtedly the overlord of the ocean. However, in terms of numbers, it does not have an advantage. No matter which type of sawfish it is, its current situation is listed as "critically endangered".

The teeth of sawfish are the main reason for the decline in their population, because such a long and toothed beak can easily be entangled in various fishing gear, resulting in a high mortality rate from bycatch. On the other hand, the collection value of the beak and the edible value of the sawfish itself also lead to their mass hunting.

The beak is entangled in fishing ropes. Source: oceantoday

In addition, sawfish mainly live in shallow sea coasts, estuaries, and even freshwater rivers, which highly overlap with areas of human activities such as fishing and boating, further compressing the sawfish's habitat.

Once upon a time, sawfish were found along the coastlines of more than 90 countries, including the Pacific, Atlantic and Indian Oceans. Today, sawfish are only found near the coastlines of a few countries and regions such as Australia, Brazil, Southeast Asia and the United States. In order to protect sawfish, many countries are also working hard to gradually establish sawfish protection laws to help them restore their former glory.

Author: Fish

Editor: Dong Xiaoxian

Reviewer: Liu Kun and Li Peiyuan