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Written by Seven Kings
As you know, there are super ferocious piranhas in the Amazon rivers. So in such a river, can other fish not survive?
In fact, there is a fish in the Amazon River that will not be bitten by piranhas, but will bite the piranhas to pieces, and it is the Brazilian arapaima that is no less legendary than the piranha. The Brazilian arapaima has a long family history, full of "god clothes", and is a grandfather who likes to take a baby, but he has suffered a disaster because he has to breathe air. Let's talk about its story today.
Brazilian Arapaima Image source: Smithsonian's national zoo
Arapaima (Arapaima) comes from Brazil, Peru and Guyana in South America and is the largest freshwater fish in the world. Its name accurately describes its appearance. The tongue of the Brazilian arapaima is stiff and cannot be skimmed. But such a mouth is mainly to match their eating habits: the Brazilian arapaima has a mouth, creates a low-pressure zone, and then sucks the fish and shrimp into the mouth like a vacuum cleaner, and the stiff tongue can crush the food with the mouth.
The Brazilian arapaima is also a giant of the fish. The most common species in Arapaima gigas (Arapaima gigas) can grow to 1.7 meters long at the age of 3, and the adult fish are 2 meters long, weighing more than 100 kilograms, and are about as fat as dolphins. Because of the size of this titan in the water, the Brazilian arapaima is also known locally as the "giant of the Amazon".
Using the dominant giant physique as their opening statement is really a bit aggrieved, in fact, the Brazilian Arapaima's skill tree is full of magical skill points.
First of all, the Brazilian arapaima is a peculiar branch of the evolutionary tree, and in this life they have no close relatives and are quite lonely.
Brazilian arapaima, like the crucian carp we usually eat, is a bony fish. The bony fish is divided into 4 families, and the euteleost family that has achieved great success in this world is the family of carp and perch, and this family also contracts most of the human fishery.
The one to which the Brazilian arapaima belongs is the most primitive of the four families, and the fish are rare. There are only 4-5 species of arapaima, and the researchers are not sure about the numbers that this hand also counts, because they are too small.
In fact, The Brazilian Bony Tongue fish belong to osteoglossomorpha, whose ancestors appeared in the Jurassic Era 187 million years ago. About 23 million years ago, the role of the Brazilian arapaima was evolved and brushed, and it became one of the oldest freshwater fish on Earth. The fossil record shows that over the next 23 million years, the shape of the Brazilian arapaima changed little, so it is also known as a "dinosaur fish".
Because of its distinctive pedigree, Arapaima Brassica has traits that many other fish species do not have. For example, the Brazilian Arapaima has inositol pentaphosphate (IPP) in its blood. It should be known that inositol pentaphosphate is widely found in the blood of reptiles and birds, but it is the only one in bony fish.
Its size and antiquity are not the most special features of the Brazilian Arapaima. Their tongues are as hard as their bones, and their scales are harder than their bones, almost the size of the fish. But curiously, the Brazilian arapaima must breathe air regularly or drown in the water.
In the Amazon basin, the dry and rainy seasons are constantly alternating. During the dry season, the river evaporates in large quantities and the living space of the fish is compressed.
In the seasonal lake caused by the dry season, the piranha (Serrasalminae) is the main predator, while the Brazilian arapaima has to get close to more than 30 species of piranhas. Interestingly, piranhas eat other fish, mammals, and birds, but they can't eat Arapaima because they have scales and thick skin.
The skin of the Brazilian arapaima, which accounts for 10% of the body weight, is so strong and durable that it can be used to make bags, shoes and furniture. Their scales are stronger and can break the teeth of piranhas.
The scales of the Brazilian arapaima are the largest of the freshwater fish, reaching up to 10 cm in length. Their fish scales are divided into two layers, the outer layer is rich in calcium, hardness is similar to ceramic, and the lower layer is collagen fiber. Soft on the inside and tough on the outside, this combination is a bit like human teeth.
Studies in recent years have found that their fish scales have a Bouligand structure. Stomatopoda, which can punch the power of a .22 caliber long rifle bullet, does not break itself, relying on the Bollinger structure.
Bollinger root structure of the scales of the Brazilian arapaima. Image source: uscd.edu
The Bollinger root structure resembles a melaleuca. Its advantage is that in the case of external forces, each layer of this mille-feuille can be rearranged, thus "dissipating" the external forces.
In 2012, Marc Meyers, a materials science researcher at the University of California, San Diego, and colleagues used the teeth of a red-bellied piranha (Pygocentrus natteri) to bite the scales of the Brazilian bony tonguefish, and the piranha's teeth were broken.
You know, a 1 kg piranha has a bite force of 20 Newtons. However, to bite through the scales of the arapaima requires a bite force of 1260 Newtons, and the piranha's teeth are far from enough. In fact, because the scales of the Brazilian arapaima are too hard, the chef uses a warhammer when descaling.
Now, many researchers are making body armor based on the scales of the Brazilian arapaima. In 2018, researchers at the University of Science and Technology of China developed a bionic armor material that mimics the scales of the Brazilian arapaima. The study was published in the National Science Review.
However, the Amazon rivers not only have piranhas, but also have a more terrible hypoxia environment than piranhas. Since the Amazon plains have dry and rainy seasons, the Amazon rivers also flood seasonally. When the dry season comes, the space of the river water is not only smaller, but also full of decaying organic matter, and the oxygen content is very low. How to breathe in this stinky gutter has become a big problem.
In order to adapt to the regular lack of oxygen, the Brazilian arapaima was forced out of a snakeskin skill, which is to breathe air. In fact, 80% of the oxygen in the Brazilian arapaima is obtained through breathing air, and less than 20% comes from water.
Arapaima can breathe air because they abandon the gills and breathe in the swim bladder.
Their swim bladders are the "lungs" they use to breathe gases, known as labyrinth organs by researchers. The maw of the Brazilian arapaima completely envelops the kidneys, and the blood vessels that supply blood to the kidneys pass through the renal portal venous system, which in turn is connected to the heart, so the swim bladder can transmit oxygen to the heart.
Arapaima of Brazil (blue) and air inside (yellow). Image source: (DOI) 10.3389/fphys.2020.00260
Like the lungs of real people, in order to increase the surface area, the bladder of the Brazilian arapaima is covered with folds. Using this huge surface area, the Brazilian arapaima turns the swim bladder into a diving oxygen cylinder.
Their breathing is achieved by means of a cheek," called a buccopharyngeal pump. Using the swim bladder, the Brazilian arapaima can survive dehydration for 30 minutes.
At the same time, the gills of the Brazilian arapaima have lost most of their functions.
Arapaima brassica gradually loses the ability to breathe in the gills as they grow up. As you can see from the picture, the gills of the Brazilian arapaima when they were young were potholed and the surface area was quite large, but when they grew up, the gills became mallets.
Gills at 10 g of arapaima (top) and gills at 1000 g (bottom) Image credit: Encyclopedia of Fish Physiology, 2011
You may want to say, even if the gills are not of great use, keeping them will not hinder things, why should they gradually become mallets?
It is true that the gills of fish obtain oxygen from water through diffusion, because more oxygen is dissolved in water than in the fish. But in turn, electrolyte levels such as sodium and chloride ions in fish are also higher than in fresh water. If the gills are too "leaky", the fish may lose the electrolytes in the body.
The researchers speculate that the gills of the Brazilian arapaima may have been to prevent the loss of electrolytes through the gills. In fact, the gills of some fish also thicken when the body does not need much oxygen, reducing the loss of electrolytes, and the gills of fish become thinner when oxygen consumption increases, such as goldfish (Carassius auratus). But such irreversible changes as the Brazilian arapaima are very rare.
Although the bladder of the Brazilian arapaima is about equal to that of the lungs, their gills still have the effect of removing carbon dioxide, so they still cannot completely leave the water to live.
And because the swim bladder basically replaces the gills, and the gills cannot be completely abandoned, the Brazilian arapaima has a fatal hard wound: the blood trough is too short. If the Brazilian arapaima do not float to the surface for 15 minutes to breathe the "oxygen tank", it will make itself suffocate, but they will not be able to survive completely dehydrated. This physiological setting of the Brazilian arapaima is the so-called empty blood gold suit.
And because the Brazilian arapaima must float to the surface of the water for ventilation, this invincible skill has become a bug after the arrival of humans. Humans are adept at using the time window of the Brazilian arapaima to hunt.
Why do humans kill Arapaima Brassica?
If you guessed it right, the meat of the Brazilian arapaima is said to be delicious. As early as the 1980s, researchers found that the muscle cells of fish that can tolerate hypoxia are larger in diameter, including the Brazilian arapaima, so the meat of the Brazilian arapaima will be thicker, closer to animal meat. Coupled with the fact that Arapaima brassica does not have fine spines and does not prick its mouth, The locals in the Amazon have traditionally had the custom of preying on Arapaima.
However, due to overfishing, in the 1970s, the Brazilian arapaima was extinct near the major cities in the Amazon Basin. Thus, in 1986, arapaima of the Brazilian arapaima was listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). In 2001, Brazil issued a decree prohibiting the commercial fishing of Arapaima brassica outside a few specific areas.
A Brazilian arapaima that cannot be mastered by researchers. Image credit: Shedd Aquarium/Carlson Haynes
Seeing here you may feel strange, resistant to hypoxia, the skin grows fast, this fish should not be difficult to raise, how can there be no commercialization?
This is mainly because captive-reared Brazilian arapaima are difficult to reproduce, which may be related to their peculiar parenting style.
Arapaima brassica is a child slave. Before the fish boy was born, the fish father and the fish mother would take turns to guard the fish eggs. After the small fish hatched for about 1 month, most of the fish mothers ran away with their butts, leaving the fish father to bring his own baby.
The fish father will take the baby for 3 months, during which he will not let the small fish drive himself too far, and in the face of danger, the small fish will hide in his mouth. Considering that arapaima is generally sexually mature at 4-5 years old and has a lifespan of less than 20 years, the time for the fish father to take the baby is really not short.
Fish dads may rely on the "milk" they produce for their children.
Yes, Arapaima Brassica "produces milk" during the breeding season, both male and female. They have two small holes in their brain shells, and white "Wahaha" will flow from the brain holes. This "milk" is not the same as human milk, but it is very similar to Wahaha, there is no nutrition, but children love to drink.
In 2017, researcher Lucas S. Torati and colleagues at the University of Stirling in the United Kingdom found that the "milk" of arapaima is secreted by their inner ears, eyeballs and central nervous system, containing hormones such as prolactin, Stoscalcitin, and a large number of proteins related to immunity.
Researchers speculate that this "milk" has the effect of coordinating parent-child relationship and strengthening the immunity of fish pups. YuZi often meets with his parents, perhaps just to take a bite of his parents' "brain juice". The biggest obstacle to artificial breeding of Arapaima Brassica may be in this "brain juice".
In any case, despite such a series of god suits, parenting soft power and a long standby history, the Brazilian arapaima cannot adapt to the Anthropocene, and the number is so low that the International Union for Conservation of Nature (IUCN) cannot count, and it is about to hang on the Earth server. This is the pain of breathing.
Arapaima Brassica: Big and hard will also lose, the key is to survive enough.
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