Time：2023-03-27 13:28:19 source：ucutxmastrees.com author：Mammal Read：484次

The strange fish shaped like a water snake travels between freshwater and the ocean, and its spawning place is still a mystery

The European eel is a bizarre fish that has fascinated many biologists with its offbeat habits, which have a dual character.

They grow to maturity in fresh water and set off in a fall to swim thousands of kilometers or more across the Atlantic Ocean to their spawning grounds. The fry follow the ocean currents back to freshwater waters. For these tiny animals, it's a massive migration, defying hardship and danger, heading towards their destination. Is it a fish or a snake? European eel is a medium-sized fish. When adult European eel is fully mature, it can be up to 1.2 meters long and weigh about 6.6 kilograms. However, most European eels can only grow to 2/3 of this size, and most individuals are due to predators. Or humans hunted and killed and couldn't grow to such a large size. These strange tubular fish are often mistaken for snakes due to their elongated bodies and sinuous swimming patterns, which are caused by ripples formed by the action of muscles on the body surface. The lack of thoracic and pelvic fins on the sides of their bodies and the reduction of their operculum to a small opening make them look more like water snakes and are often mistaken for snakes. Breeding in the sea European eels are also known as common eels. They are widely distributed and are one of the closest relatives in the eel family. All eels adopt a special migratory lifestyle called "breeding in the sea". They start their life journey as plankton-like juveniles in the ocean, grow to adulthood and return here to breed, after which they complete the rest of their life journey and die here, but live in freshwater in the middle of their lives, sometimes The freshwater active area is very far from the birth sea. Their guts have special adaptations that allow them to survive the transition from fresh water to water, which is very rare in fish. European eels only have one chance to reproduce in their lifetime, and reproduction represents the end of their lives, and they die quickly after laying eggs in deep water. The long-lived eel Eel mussel is an extremely long-lived fish. Like other species of the Eel family, the European catfish is also exceptionally long-lived. Male European eels live 10 to 12 years in freshwater to feed and grow, while female European eels grow even longer, sometimes up to 20 years, and there are yet-to-be-verified reports of 30 years. During their freshwater life, they move among a variety of habitats including tidal rivers, swamps, ponds, drains, and streams. Surveys have shown that juvenile Europeans prefer to be located in the lower reaches of the river, while older, larger individuals are often found in the upper reaches of the river. Strong adaptability The wide distribution of the eel family is related to its strong adaptability. During the day, the European eel hides in cluttered roots and underwater vegetation to avoid its main predators, egrets and scorpions. They come out at night to hunt invertebrates and other small prey, and sometimes carrion. Remarkably, their mucus-covered skin allows them to survive short periods of time in water-deprived environments, and can also glide across the ground to find food or occupy new habitats. European eels spend the coldest months hibernating in the mud at the bottom of rivers and ponds in winter. European eels that progress to sexual maturity eventually leave freshwater habitats and migrate long distances to breed in the ocean. Migration peaks on autumn nights, especially between the last quarter and new moon. The signal for the departure of the European eel is a drop in water temperature and a sudden increase in water volume due to heavy fall precipitation. With the help of ocean currents, European eels can move up to 50 kilometers per night in large groups. When European eels approach the coast, their stomachs contract and stop feeding. Their eyes have almost doubled in size due to migration in the deep ocean. Their dark bodies also turn silver, presumably to facilitate shelter in the open ocean. Little is known about the egg-laying behavior of European eels, and from current research, we have not observed them in the wild. Scientists speculate that they lay a very large number of tiny eggs, which float with ocean currents and eventually hatch into transparent juveniles called larvae. The juveniles are so small that they are almost invisible and very easy to avoid predators, but even so, after 2 to 3 years of drifting, only a very small number of European eel fry can safely reach the estuary. At the estuary, the fry grow into pencil-sized juveniles, which then travel up the river like a swarm of spaghetti to continue their life cycle. The Mystery of the Spawning of the European Eel Although many studies have been carried out on this fish, the spawning place of the European eel has not yet been found, but it is speculated that it may be located in the Sargasso Sea east of Bermuda in the western Atlantic Ocean. So it is speculated that from here, the fry can return to Europe with the help of ocean currents. They first move northward by relying on the powerful Gulf Current, which originates from the Caribbean Sea and transports warm and high salinity water to the north, and then they follow the North Atlantic warm current and continue to move toward the north. Drift northwest, past the coast of Western Europe. Through the inference of this migration route, the starting point of eel travel is very likely in the Sargasso Sea. An international research project is exploring this question. Scientists are installing satellite trackers on these migrating silver European eels in the fall, hoping to obtain data on their migration paths in the ocean and identify their likely final destinations. Another study of European eels reared in swimming lanes showed that they are very efficient swimmers, able to complete a simulated migration of about 5,500 kilometers without feeding, which is extremely rare in fish. But more research is needed to answer this question, because the Sargasso Sea is about 8,000 kilometers away from the northernmost area of ​​activity for this species. Can they really migrate that far? At present, the survival situation of European eel U is very serious. In the past, there were a lot of European eel U at the mouth of every major river in Europe. But that scene is no longer there, with the number of young eels arriving on European shores falling by at least 90 percent since the 1970s. Some experts believe that this population decline is a natural phenomenon that fluctuates periodically and will not last for long, but most experts believe it is a long-term irreversible trend. Overfishing is one cause of this phenomenon. Other important threats may include pollution, barriers to migration—some tidal dams and hydroelectric dams, and nematode infestations, all of which have contributed to the dramatic decline of this species, if we don’t protect it sooner rather than later. species, their survival will be threatened.

(责任编辑：Zoo)

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