Fish are bony scales, gill breathing, swimming through the tail and trunk and the coordination of fins swimming and feeding by the upper and lower jaws, belonging to the chordate phylum of vertebrates, generally people divide vertebrates into fish (53%), birds (18%), reptiles (12%), mammals (9%), amphibians (8%). According to the statistics of the late Canadian scholar "nelson" in 1994, there are 24618 species of fish in the world, accounting for more than half of the named vertebrates, and new species of fish are constantly being discovered, with an average of about 150 species per year, which should have increased by more than 1500 species in more than a decade, and the current global named fish species are about 32100 species.
Fish is the oldest vertebrate. They inhabit almost all of the planet's aquatic environments – freshwater lakes, rivers to saltwater seas and oceans.
There are about 32,000 species of fish that have been found in the world, and the fish live in the water, distributed in the ocean and freshwater, two-thirds of the ocean lives in the ocean, and the rest live in freshwater. There are 2,500 species in China, of which there are more than 100 kinds of medicinal animals, and the common medicinal animals are seahorse, sea dragon, yellow eel, carp, crucian carp, sturgeon (maw for fish maw glue), giant yellow fish (otolith for ichthyromatis) liver oil (vitamin A and vitamin D) the main raw materials. Hydrolyzed proteins, cytochrome C, lecithin, cerebral phospholipids, etc. can be extracted from various fish meats, and the liver and ovaries of puffer fish contain a large amount of tetrodotoxin, which can be extracted to treat neuropathy, spasms, tumors and other diseases. The bile of large fish can be used to make "biliary pigment calcium salts", which are used as raw materials for artificially making bovine yolk. The differences between the various orders of fish are as great as between the classes of terrestrial vertebrates. Fish are generally considered to be spiky and spindle-shaped, streamlined, finned, gill-breathing aquatic animals, but many more species do not meet this definition. Some fish have extremely long bodies, some are extremely short, some are flattened on the sides, some are flattened, some have large fins or complex shapes, some are degenerated and even digested; and the shape of the mouth, eyes, nostrils, and gill openings varies greatly. Fish is an important food for humans. Overfishing, pollution and environmental change can all destroy fish stocks, which prey on and help control mosquito-borne diseases such as malaria. Fish are important laboratory animals in behavior, physiology, ecology and medicine.
Ornamental fish
Fish are mostly cold-blooded, and a very small number are warm-blooded, breathing with gills, with jaws and fins. Extant fish can be divided into two main populations: cartilaginous fish (such as sharks) and teleost fish (linear fin and wavy fin fish). Both groups of fish first emerged from the early Devonian period. The more advanced group of linear finfish, called teleost fish, began to evolve during the Jurassic period and has become the fish with the largest number of individuals. There are also several species of fish that have become extinct.
Fish, accompanied by human beings through more than 5,000 years of history, and human beings have formed an indissoluble relationship, becoming a very important food and ornamental pet in human daily life, but people know very little about what animals are "fish" and how to define fish. With the development of science, people's definition of fish has also changed a lot.
Nearly half a billion years ago, a major leap took place in the course of life on Earth, with the emergence of the earliest fish-shaped animals, which opened the prelude to the history of vertebrates, which led to the development of the animal kingdom and entered a new historical stage. Real fish first appeared more than 300 million years ago, in the entire long history process, once survived a large number of fish, has long been with the passage of time and extinction, living on the earth fish, only a small number of species that appeared and evolved later.
Ornamental fish: peacock fish
Humans have long been able to identify species and give names, usually referred to as "fish" includes all animals in the water, so many animals living in the water are named fish, and whales, seals, giant salamanders (baby fish), squid, squid, octopus, starfish, jellyfish, sponges, Wenchang fish, etc. are confused with fish.
Twenty thousand years ago, the ancient Greek philosopher Plato defined fish as follows: "This class [of fish] is created by something completely ignorant and unconscious." The Lord of Transformation thought that it was no longer worth it to give pure breath in this category, because they were the offspring of all kinds of evil and there were unclean hearts. The Lord of Transformation threw them into the water, causing them to breathe through the deep sludge of the divine and pure air. This is how fish and oysters, as well as all other aquatic animals, have been separated far away as punishment for the great sin of ignorance." Plato's views are full of creationism. Due to the development of modern science, this view has long been completely rejected.
At the beginning of the Han Dynasty in China, "Erya" has divided animals into four categories: insects, fish, birds and animals, of which fish include fish, amphibians, reptiles and other low vertebrates, as well as whales and shrimp, crabs, shellfish and so on.
The 18th-century Swedish naturalist Carl von Linne (1707-1778), who founded modern taxonomy, divided the animal kingdom into six classes: mammals, birds, amphibians, fish, insects, and worms in his book Natural Systems. In 1859, the British biologist Darwin published the book On the Origin of Species, which gave birth to systematic taxonomy. Since then, the definition and scope of fish have been determined.
Photo album of fish
Which animals are "fish"? Modern taxonomists define a "fish" as a vertebrate that lives in water all its life, breathes with its gills, and swims with its fins. Fish include three major groups of gardeners, cartilaginous fish and teleost fish, there are about 26,000 kinds of known fish in the world, which is the largest variety of vertebrates, accounting for about 48.1% of the total number of vertebrates.
The fish have good hearing. Scientists have found that although many fish do not have long ears on the outside, they have specially designed sound receivers that transmit sound waves to a tubular structure filled with liquid in the inner ear. These tubes have special fine hairs, called cilia, that transmit pulses of sound through a complex set of mechanisms and chemical reactions to the fish's brain, where they are processed. Otoliths are part of the auditory system, connected to sensory cells, and play a large role in the auditory/balance mechanisms of bony fish. Otoliths are valuable to scientists, who rely on otoliths to identify fish species and to determine the age of a fish — because when a fish grows, otoliths grow in a round of concentric circles every year. Under a microscope, scientists can see and count these concentric circles.
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