CATDOLL : CATDOLL: How many species of eels are there in the world?

How many species of eels are there in the world?

There are 18 species of eels in the world, of which Taiwan has four families: Japanese eels, perch eels, Celebes eels, and short-finned eels. However, only Japanese eels are the most common, and the other three are rare. They have lived on Earth for tens of millions of years, but we have only known about them for the past few decades. For example, its true spawning ground was not discovered until 1991. Its gender is most controlled by environmental factors and density. When the density is high and food is insufficient, it will become a male fish, otherwise it will become a female fish. In Taiwan's rivers, since there are very few eels, most of them are female fish.

Japanese eel fry cannot be bred artificially, mainly because eels have a very special life history that is difficult to simulate in an artificial environment. Japanese eels grow up in freshwater rivers and begin to migrate to the sea in the summer, that is, swim from rivers to the ocean to lay eggs, which is exactly the opposite of the upstream migration of trout and salmon from the ocean back to rivers to lay eggs. Its spawning ground is thousands of kilometers away in the deep sea between the Philippines and the Malay Islands. Scientists discovered this spawning ground mainly because they caught many of its newly hatched fry here.

The body length of the eel fry is about 6 cm and the weight is 0.1 gram. However, it has a narrow head and a tall, thin and transparent body like a leaf, so it is called "willow leaf fish". Its body fluids are almost the same as seawater, so it can be easily transported over long distances with the ocean current. It takes about half a year for it to drift back from the spawning grounds to the Kuroshio current and then back to the coast of Taiwan. It will only start to metamorphose into a thin and transparent eel line one month before arriving at the shore, also known as "glass fish". Therefore, from December to January every year, fishermen will be busy using hand fork nets to catch eel lines that are about to go upstream on the coast near the estuary and sell them to farmers. After the farmers buy them back and release them, the color will gradually appear, turning into yellow juvenile eels and silver adult eels. Under natural conditions, the largest eel that can be caught is 45 cm and weighs 1,600 grams.

Eels lay their eggs in the deep sea and grow in freshwater. They are ferocious, greedy, active, nocturnal, phototropic, and like flowing water and warmth.

Adult eels grow fast, and their appearance is round and cone-like, with a dark and firm color. In recent years, they are more often farmed, and their meat is crisp and tender. This fish is common all year round, but it is the most plump and delicious in summer and winter. Eels are rich in nutrition, delicious, with few bones and more meat, and have the effect of cooling down and relieving summer heat, nourishing and strengthening the body.

There is also the yellow eel, which belongs to the family Synbranchidae and is also a fish. It is also similar to a snake, has no scales, and has a yellow belly, hence the name yellow eel. Yellow eels live in mud caves in ponds or on the banks of freshwater rivers. They cannot survive without water, and when they are caught, they are covered in saliva. Yellow eels are not only a delicious delicacy with tender meat and delicious taste, but also have been known for their nourishing and medicinal effects since ancient times.

Eel is a general term for species belonging to the order Anguilla. Also known as eel, it is a fish that looks like a long snake and has the basic characteristics of fish. In addition, eels have migratory characteristics similar to salmon.

Eel, also known as unagi, is divided into freshwater eel and seawater eel. Freshwater eel species include: river eel (white eel, Shuangshan Gaixiang eel), flower eel (reed eel, mountain eel, king eel), naked back electric eel, light back electric eel, all of which are freshwater species. Sea eels include: sea eel (white eel, Japanese eel, door eel), conger eel, blind eel (blood sucking eel), snake eel or thrush, sawtooth eel, European eel.

How to distinguish whether the Qiantang River eel is authentic or not, and what are the obvious characteristics when selecting it? How to choose

1. Chondrichthyes

This system is the lowest group of existing fish, with about 200 species in the world and more than 140 species in my country, most of which live in the sea.

Its main features are:

① There are no hard bones throughout life, and the internal skeleton is composed of cartilage.

② Most of the body surface is covered with scales.

③ The gill septa are well developed and there is no gill cover.

④ Crooked caudal fin. This system is divided into two subclasses, namely, the Elasmobranch subclass and the Holocephalus subclass.

2. Osteichthyes

Bony fishes are the most numerous group of fish in the world, with more than 20,000 species. Most of them live in marine waters, and some live in fresh water.

Its main features are:

① The bones harden to different degrees.

② The body surface is covered with hard scales, round scales or comb scales, and a few species are degenerate and scaleless. The mucous glands of the skin are well developed.

③ The gill slits are partially or completely degenerated, the gills do not open directly to the body, but are protected by bony gill covers. The water flowing out of the gill slits is discharged through the posterior edge of the gill cover, and most of them have a swim bladder.

④ The fish tail is usually straight, but it can also be original or crooked.

⑤ Most are fertilized in vitro and are oviparous, and a few have abnormalities in their development.

The first fish were round-mouthed, jawless fish that appeared on Earth 450 million years ago during the Cambrian period. Fish are easily distinguished by their appearance and form the largest group of vertebrates: there are more than 22,000 species of fish out of a total of 50,000.