Mention of fish we are more familiar, such as: carp, grass carp, silver carp, bluefish, etc., these fish for the common edible fish, the individual is not large, generally no more than 20 pounds, then you have seen the largest freshwater fish how big?
For example, the common silver carp and grass carp, more than 20 kilograms of individuals are rare, although they can exceed the potential of 100 pounds to become "giant freshwater fish", but it takes a lot of time, and we just did not give them this time.
Therefore, it is difficult to grow up, even if the individual blue fish with a long life and fast growth rate is only more than 100 pounds. So how big is the biggest freshwater fish in your mind?
Global Times reported on June 22: 300 kg! Cambodian fishermen catch the world's largest freshwater fish, about 4 meters long. Fishermen in the southern part of Cambodia's Shangding province catch a stingray 3.98 m long and 2.2 m wide in the Mekong River. Scientists have determined that the stingray, weighing 300 kilograms, is the largest freshwater fish ever discovered by humans.
After the giant stingray was dragged ashore by more than a dozen people, scientists installed a tracking device on it and released it to track and detect its movement and behavior in the river.
According to the Guinness Book of World Records, the world's largest freshwater fish was the Mekong catfish (293 kg). This stingray will potentially become the world's largest freshwater fish.
4 meters long and 300 kilograms, such a large freshwater fish is not only in the Mekong River, but even in the world is relatively rare, then we can't help but have a question, what is this fish, why is it so big?
Giant stingray
Giant stingrays belong to the suborder Stingray, Stingrayidae, Sandy Stingray, Cartilage series, native to southern Asia, Thailand, Borneo and so on.
We know very little about the giant freshwater stingray, because this fish is discovered relatively late, and scientists have done little research on it, such as: life cycle, feeding mode at various growth stages, breeding methods, etc., and do not know much.
It was first observed in 2004 and attracted the attention of scientists, when the individuals found were not very large. In 2006, American biologist Zab Hogan found the head of a fishing company in Cambodia, Razi Humphrey, as a guide to catch giant fish in the Mekong.
The research project, part of the Mega Fish Statistics Project funded by the National Geographic Society, lasted three years and began with a 2006 research program in which 40 stingrays were caught in the Mekong River in a year, and the largest one weighed 485 pounds (220 kg).
The freshwater fish, though slow-moving, has its own "weapon", and that is the long tail, and Australian wildlife expert Steven died in 2006 after being pierced through the chest by a stingray's barb. So fishing or studying this freshwater giant fish also carries a lot of risks.
The stingray is brown to gray in color, broad and flattened in shape, has a long, whip-like tail, and often buries itself in sand or silt river bottoms, and breathes through holes in the top of the body or water spray holes.
Studies have shown that giant stingrays have sensors that detect the electric field of animals, can sense the dynamics of their prey in advance, they bury their bodies in sand, or in silt, or in obstacles, if there is prey approaching, it will prepare in advance and launch an attack, for carnivorous, mainly by latent predation, can catch the food needed to meet its huge size.
Their flattened, broad body and long whip-shaped tail, which have hardly changed for at least millions of years in the Mekong, show once again that their hunting strategy is very effective, so what kind of river is the Mekong River?
Mekong
The Mekong River originates on the northeastern slope of the Tanggula Mountains in Qinghai Province, called the Lancang River in mainland China, and exits from Xishuangbanna Dai Autonomous Prefecture in southern Yunnan Province, passing through five countries: Myanmar, Laos, Thailand, Cambodia and Vietnam.
Flowing into the South China Sea near Ho Chi Minh City, Vietnam, the part of the mainland is called the Lancang River, and the downstream section is called the Mekong River, with a total length of 4,880 kilometers and a total basin area of 810,000 square kilometers.
The Lancang River basin is basically within the mainland, with a length of 2161 kilometers (including 31 kilometers of the border section between China and Myanmar), a basin area of 190,000 square kilometers, and a mainland territory of 167,400 square kilometers, which is called the Mekong River downstream.
The mekong main stream valley is wider, more curved, and affected by the dry season and the rainy season, the water level drops greatly, when the rainy season comes, the water level rises, the water surface is wide and cannot be seen at a glance, and when the dry season comes, the water level is lowered, and only the main river has water flow.
This climate of alternating dry and rainy seasons has created a large number of fish in the Mekong, because with the arrival of the rainy season, a large number of plants on the shore are submerged, there is a lot of food, fish enter shallow water from deep water to feed, and when the dry season comes, the fish level is lowered, and the fish return to deep water.
An expert said before: "There are more fish living in the Mekong River basin than in any other river in the world", the reason for this is because of the abundance of food and the right temperature, resulting in fish growth, rapid reproduction, and the formation of huge individuals.
According to scientists, there are about 1200 species of fish in the Mekong. In fact, it is not too rigorous, because it is only inferred that because the countries along the Mekong River belong to underdeveloped areas, the protection of the environment, the protection of fishery resources, and the statistics of fishery resource types are not taken to heart.
For most people along the Mekong, being able to fish in the Mekong, being able to feed and feed their families is already good, and few locals will protect the fish. So why is there so much fishing, and there are so many large fish such as giant stingrays, giant catfish?
How do giant fish survive?
The cities along the Mekong River in the lower reaches of the Lancang River are numerous and densely populated, with millions of fishermen and practitioners relying on water to draft water, and do not pay attention to protecting the water environment.
As we all know, there are 3 main reasons why fish want to grow into giant individuals, one is that the water surface is large and the depth is sufficient, and only the fish with large water surface have a certain chance of escaping human capture again and again.
Second, there is a lot of food, fish want to grow into a giant individual, need a lot of food, especially carnivorous fish, a day's food can even reach 10-20% of the body weight, if there is a shortage of food, their growth rate will be greatly slowed down.
Third, the temperature is suitable, the fish itself does not produce body temperature, its body temperature changes with the change of water temperature, when the water temperature is too low when the growth rate of fish is very slow, although it can also grow into a giant fish, but the probability is too small. So can the environment of the Mekong River meet these 3 requirements?
First of all, the annual runoff of the Mekong River is 475 billion cubic meters, while the annual runoff of the Mainland Yangtze River is only close to 1 trillion cubic meters, which proves that the water resources are abundant.
The average width of the Mekong River is 800-2500 meters, close to the border of Laos and Cambodia, there are 50 kilometers of river channels, when the rainy season comes, the width reaches 14 kilometers, and the river bends are more, the catchment area is more, providing sufficient innate conditions for the growth of fish.
The second is food, mentioned above that the Mekong River is divided into dry season and rainy season, there is no shortage of food, heavy rain in addition to bringing a lot of food, but also can make the river water become turbid, turbid river water can provide protection for fish, so that they will not be extinct fishing, although the catch is large, but the rate of decline in fishery resources is not so fast.
Finally, the temperature, after the Mekong River flows out of the mainland, most of the areas flowing through belong to the tropical monsoon climate, which is characterized by high temperatures throughout the year, the coldest average temperature is also above 18 ° C, and the temperature is high And the fish grow fast.
Winters are popular from the northeast monsoon of the mainland, where precipitation is scarce, and summers are abundant due to the southwest monsoon of the Indian Ocean, with abundant precipitation, with an annual precipitation of 1500 to 2500 mm in most areas, but some areas are far more than that. Abundant rainfall provides sustainability for the life and growth of fish.
The wide water surface area, abundant food, and suitable temperature provide sufficient conditions for the giant fish of the Mekong River. So fish have the characteristics of migrating and drowning, can giant stingrays swim upstream along the Mekong River to the Lancang River?
Can stingrays swim upstream along the Mekong River to the Lancang River?
No matter what kind of fish have the characteristics of retrograde swimming, that is, swimming against the water, some are reproductive migration, some are for habitat, some are for food, and stingrays are no exception, the Mekong River belongs to the lower reaches of the Lancang River, they will follow the current to the Lancang River I. The answer is no! There are 3 reasons for this.
First, the obstruction of alpine canyons, the northeast slope of tanggula mountain in Qinghai Province, where the Mekong River originates from the mainland, the source altitude is as high as 5200 meters, the terrain in the basin is complex, the upstream belongs to high altitude areas, the middle reaches belong to alpine canyons, the river valley is deeply rooted between the Hengduan Mountains, and the mountains are high and deep.
The lower reaches of the sea are generally below 2500 meters above sea level, especially in Laos, the Khong Waterfall appears, the waterfall drop reaches 14 meters, the width reaches more than 10 kilometers.
Blocked by high mountains and valleys, the Lancang River is turbulent in the territory of the mainland, when flowing abroad due to the sharp decline in altitude, and the blocking of giant waterfalls, such a large drop in many fish is difficult to swim backwards, which is also a reason why the Lancang River and mekong river fish in the mainland, whether they are species or individuals, are very different.
The second is climate change, stingrays live in the lower reaches of the Mekong River, these places belong to the tropics, the minimum average temperature in winter is also 18 °, while the mainland is only in the tropics at the border with Vietnam, where there is the only tropical rainforest on the mainland.
Most of the upper reaches of the Mekong Lancang River belong to the high-altitude climate, the temperature is relatively low, even in addition to the mountains, canyons, waterfalls blockage, stingrays are difficult to survive in these places, after all, the evolution of organisms can not be completed in a short time.
Third, the scarcity of food, the growth of any fish is inseparable from food, the middle and lower reaches of the Mekong River belong to the tropics, the rainfall is abundant, regardless of the variety of fish, or the density is relatively large, and with the advent of the rainy season, the water level soars, the water quality is turbid, which is conducive to the latent feeding of this slow-moving fish.
Due to the cold weather in the upper reaches of the Mekong River, regardless of the species of fish, the density is relatively small, and the scarcity of food is not suitable for the growth of large fish. There are giant fish in the Lancang River, such as the scientific name of the melon fish, but now the density is getting less and less.
From the obstruction of mountains, canyons, waterfalls, climate changes, and the scarcity of food, these three aspects can be seen that the giant stingray living in the Mekong River is almost impossible to swim against the current to the Lancang River.
Finally: although there are more species of giant fish in the Mekong River, their living environment is not optimistic, as the catch decreases year by year, many locals have begun to farm fish in the river, it is said that the mekong river farmed fish, the catch has exceeded the wild fish.
And this 4-meter-long giant stingray weighing 300 kilograms, does this mean that the growth environment of Mekong fish has been improved? This is not the case, because fish stocks do not increase overnight, nor can they be achieved in a short period of time by breeding and stocking. Although the Mekong is rich in biodiversity, overfishing and pollution still threaten its fragile ecosystem.