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Fish is the oldest vertebrate. They inhabit almost all aquatic environments on earth-freshwater lakes, rivers, saltwater seas and oceans.

Pictures of Common Fish (35 photos)

There are about 32,000 kinds of fish in the world. Fish live in water, distributed in the ocean and fresh water, of which two thirds live in the ocean and the rest live in fresh water. There are 2,500 species in China, of which 100 is a kind of medicine. Common medicinal animals are the main raw materials of cod liver oil (vitamin A and vitamin D) of hippocampus, syngnathus, Monopterus albus, carp, crucian carp, sturgeon (swim bladder glue) and Pseudosciaena crocea (otolith is brain stone). Hydrolyzed protein, cytochrome C, lecithin and cephalin can be extracted from various fishes. The liver and ovary of puffer fish contain a lot of tetrodotoxin, which can be extracted to treat diseases such as neuropathy, spasm and tumor. The bile of big fish can be extracted as "bile pigment calcium salt", which is the raw material for artificial production of bezoar. The difference between fish species is as great as that between terrestrial vertebrates. It is generally believed that fish are slippery, spindle-shaped, streamlined, finned and gilled aquatic animals, but more species do not meet this definition. Some fish are particularly long and some are particularly short; Some sides are flat, some are flat; Some fins are large or complex in shape, and some degenerate or even digest; The shape and position of the mouth, eyes, nostrils and gill openings vary greatly. Fish is an important food for human beings. Overfishing, pollution and environmental changes will destroy fish resources, which will help control mosquito-borne diseases such as malaria. Fish is an important experimental animal in behavior, physiology, ecology and medicine.

Fancy fish

Fish are mostly cold-blooded animals, and very few are warm-blooded animals. They breathe through their gills and have jaws and fins. The existing fish can be divided into two categories: cartilaginous fish (such as sharks) and bony fish (fish with linear fins and wavy fins). Both groups of fish first appeared in the early Devonian. A more advanced group of linear finned fish, called bony fish, began to evolve in Jurassic and has become the most individualized fish. There are also several extinct fish.

Fish, accompanied by human beings for more than 5,000 years, has formed an indissoluble bond with human beings and has become an extremely important food and ornamental pet in human daily life. However, few people know what an animal is a fish and how to define it. With the development of science, people's definition of fish has changed a lot.

Nearly 500 million years ago, the life course on the earth took a great leap, and the earliest fish-shaped animals appeared, which opened the prelude to the history of vertebrates, thus leading to the development of the animal kingdom and entering a new historical stage. Real fish first appeared more than 300 million years ago. In the whole long historical process, a large number of fish have survived, and with the passage of time, they have already become extinct. Fish that live on the earth are only a tiny part of the species that later appeared and evolved.

Ornamental fish: peacock fish

Humans can identify species and name them long ago. Generally speaking, "fish" includes all animals in the water, so many animals living in the water are named fish. Whales, seals, giant salamanders, squid, octopus, starfish, jellyfish, sponges and amphioxus are all confused with fish.

Two thousand hundreds years ago, Plato, an ancient Greek philosopher, defined fish as: "This kind of fish is made up of completely ignorant things. The master of transfiguration thinks that it is no longer worthwhile to give pure breath, because they are descendants of all kinds of evil and have unclean hearts. The shapeshifter threw them into the water and let them breathe the beautiful and pure air through the deep mud. This is the fish and oysters and all other aquatic animals, which are separated from each other as a punishment for the great folly. " Plato's views are full of creationism. Due to the development of modern science, this view has long been completely denied.

Erya in the early Han Dynasty divided animals into four categories: insects, fish, birds and beasts. Among them, fish include lower vertebrates such as fish, amphibians and reptiles, as well as whales, shrimps, crabs and shellfish.

Karl von Linne (1707~ 1778), a Swedish naturalist in the 8th century, founded modern taxonomy. In his book Natural Systems, he divided the animal kingdom into six categories, including mammals, birds, amphibians, fish, insects and worms. 1859, British biologist Darwin published the book Origin of Species, which gave birth to systematic taxonomy. Since then, the definition and scope of fish have been determined.

Fish Album (56 photos)

Which animals are "fish"? Modern taxonomists define "fish" as vertebrates that live in water all their lives, breathe through gills and swim with fins. There are three groups of fish, namely, circadian rhythm fish, cartilaginous fish and bony fish. There are about 26,000 known fish species in the world, which is the largest group of vertebrates, accounting for 48. 1% of the total number of vertebrates. Most of them live in the ocean, and there are about 8600 species of freshwater fish. There are nearly 3,000 species of fish in China, among which about 1000 species are freshwater fish.

Fish have good hearing. Scientists have found that although many fish do not have long ears outside, they have specially designed sound receivers that can transmit sound waves to the tubular structure filled with liquid in the inner ear. These pipes have special fine hairs, called cilia, which can transmit sound pulses to the fish brain through a series of complex mechanisms and chemical reactions, and process them there. Otolith is a part of the auditory system, which is connected with sensory cells and plays an important role in the hearing/balance mechanism of teleost. Otoliths are very valuable to scientists. They rely on otoliths to distinguish the species of fish and judge the age of a fish-because otoliths grow a concentric circle every year when the fish grows. Under the microscope, scientists can see and count these concentric circles.

Animal appearance

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Spindle shaped

Fish in various forms (35)

Also known as the basic type, it is the body shape of ordinary fish, suitable for swimming in the water, and the whole body is spindle-shaped and slightly flat. Among the three body axes, the head and tail axis is the longest, the dorsal and abdominal axis is the second, and the left and right axis is the shortest, which makes the whole body streamlined or slightly flat to reduce the resistance when moving in the water, so this fish is good at swimming. Often inhabit the middle and upper water. Examples that can be used for long-distance migration: carp, crucian carp and shark.

Transverse flat type

Among the three body axes of this fish, the left axis and the right axis are the shortest, and the ratio difference between the head and tail axis and the back axis is not too much, forming a flat shape with left and right symmetry, making the whole body shape obvious and wide. Therefore, the swimming ability is worse than that of the spindle type, and it lives in the middle and lower layers of water. Long-distance migration is rare. Such as pomfret, butterfly fish, bream, mullet, swallow fish and so on.

baculiform

eel

Also called eel type. The tail axis of this fish head is particularly long, while the left and right axes are almost equal and short, making the whole body stick-shaped. Its swimming ability is better than that of lateral flat type and flat type. Suitable for digging holes in underwater soil and living in underwater sandstone.

Such as eels, eels and many kinds of sea eels.

Flat type

Among the three axes of this fish, the left and right axes are particularly long and the back axis is very short, which makes the body flat and slow, and is not as flexible as the first two kinds of benthic organisms. Like ray, ray? ? ? ? And catfish.

In addition, there are some fish that show special body shapes because they adapt to the special living environment and lifestyle, such as sea dragon, sunfish, cuckoo, flounder and box fish. Fish of any size can be divided into three parts: head, trunk and tail. It is characterized by no neck, and the head and trunk are connected and fixed, which is one of the differences between fish and terrestrial vertebrates. The dividing line between the head and trunk is the rear edge of the gill cover (teleost fish) or the last pair of branchial cleft (cartilaginous fish). The trunk and tail are generally bounded by the posterior edge of anus or the starting point of gluteal fin, or precisely by the end of body cavity or the first caudal vertebral body.

athletic ability

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abstract

Fish (7 slices)

Fish's appendage is fin, which is an exercise organ for swimming and keeping balance. Fins are composed of branched fins and fins, which are divided into two types: one is horny fins, which are not segmented and branched, and are generated by epidermis and found in cartilaginous fish; The other is scale fin or bone fin, which comes from scales and is segmented, branched or unbranched, and is found in bony fishes. Fins are connected by thin fins. Bone fin can be divided into two types: fin thorn and soft thorn. Fin spines are formed by the deformation of a fin. They are hard spines that are neither branched nor segmented, and are only found in higher fishes. The soft strip is soft and jointed, and its distal branch (called branched fin) or unbranched fin (called unbranched fin) is formed by merging the left and right halves. Fins are divided into odd fins and lateral fins. Lateral fins are a pair of fins, including 1 pair of pectoral fins and ventral fins, which are equivalent to forelimbs and hind limbs of terrestrial vertebrates. Odd fins are unpaired fins, including dorsal fin, caudal fin and gluteal fin. The basic function of dorsal fin and gluteal fin is to keep balance, prevent tilting and swaying, and help swimming. Like a rudder, the tail fin controls the direction and pushes the fish forward. Common fish have the above five kinds of fins, chest, abdomen, back, buttocks and tail. But there are a few exceptions, such as Monopterus albus without lateral fins, whose odd fins are also degraded; Eels have no ventral fins; Electric eels have no dorsal fins and so on.

tail fin

Determine the direction of movement, provide the power to move forward, if lost, the fish will not turn. According to the relationship between the shape and position of the coccyx, the caudal fin can be divided into four types:

Fish (17)

Circular caudal fin: the caudal fin is a leaf, and the caudal vertebra extends to the posterior end of the caudal fin, which is divided into dorsal-ventral symmetry and pointed caudal fin, which is more common in embryonic and larval stages of fish.

Oblique caudal fin: the caudal fin is divided into upper and lower leaves, and the end of the caudal vertebra is slightly curved and extends upward into the upper leaf of the caudal fin. The upper leaf is long, and the lower leaf is small and slightly prominent, forming a curved caudal fin with asymmetric inside and outside. Common in modern cartilaginous fish and some bony fish. Such as sharks, sturgeons and so on.

Orthomorphic caudal fin: divided into two leaves symmetrical up and down. The end of coccygeal vertebra only reaches the base of caudal fin, but slightly upturned, leaving traces of curved coccygeal vertebra. The caudal fin is completely symmetrical in shape, and the lower lobe is supported by extra coccyx fragments. Orthomorphic caudal fin is one of the characteristics of higher fishes. According to the change of fin shape, it includes many kinds of fin shapes.

Prototype caudal fin: the end of coccygeal vertebra extends straight to the end of tail, which is round, not as sharp as the round tail. The upper and lower leaves of the caudal fin are roughly equal. This is a primitive tail shape, which is found in Cyclocephala, and fish are only found in young fish.

pectoral fin

Keep the fish in balance. If you lose it, the fish will swing from side to side. It is equivalent to the forelimbs of terrestrial animals and attached to the chest at the rear edge of the gill cover. It has the functions of moving, balancing and mastering the direction of movement for fish. When the fish stops moving forward, the pectoral fin is used to control the balance of the fish; When swimming slowly, pectoral fins play the role of rowing; When driving at high speed, the pectoral fin is close to the fish, and when it is lifted, it can slow down and brake; When one side of the pectoral fin clings to the fish and the other side is lifted, the fish turns to the lifted side to help the caudal fin act as a rudder.

ventral fin

Keep the fish in balance. If you lose it, the fish will swing from side to side. It is equivalent to the hind limbs of terrestrial animals, and has the functions of assisting dorsal fin and gluteal fin to maintain the balance of fish and assisting fish to lift and turn. The position of ventral fins varies from fish to fish, and the ventral fins of cartilaginous fish are generally located on both sides of cloacal foramen. Similar in shape to pectoral fin, but slightly smaller. The ventral position of the pelvic fin of teleost is called the ventral position of the pelvic fin. This is a relatively primitive species, such as carp, salmon, catfish, herring and so on; The chest located in front of pectoral fin and behind gill cover is called ventral fin chest position, such as perch, yellow croaker and snapper; The throat between the cheeks is called ventral fin throat position, such as catfish and? Family fish. The chest position and throat position of ventral fin are advanced features of fish after evolution. These ventral fins with different positions are important symbols in the evolutionary history of fish and are of great significance in animal taxonomy.

dorsal fin

Keeping fish upright plays a key role in the balance of fish. If you lose it, you will lose your balance and turn over. But there are also some long fish, dorsal fins and anal fins that can help the body move and push the body forward quickly. For example, the dorsal fin of hairtail, the anal fin of electric eel, and the dorsal fin and anal fin of sea eel can all push the body forward. Another example is the special shape of the hippocampus, which also relies on the tiny dorsal fin movement to push the body forward. Fin type is a form of record, indicating the composition and number of fins. In Latin, the first letter of each fin represents the category name of the fin, such as dorsal fin "D", anal fin "A", ventral fin "V", pectoral fin "P" and caudal fin "C". Capitalized Roman numerals represent the number of spines. Arabic numerals indicate the number of soft strips, and the number range of spines or soft strips is indicated by "one". When spines are connected with soft strips, they are indicated by "one" and separated by ",". For example, fin carp: D..Ⅲ-Ⅳ- 17 ~ 22; p .ⅰ- 15 ~ 16； vⅱ-8-9； A...ⅲ-5 ~ 6; C.20 to 22.

The above shows that carp has a dorsal fin, 3 ~ 4 hard spines and 17 ~ 22 soft strips; 1 hard spines and 15 ~ 16 soft strips in pectoral fin; There are 2 hard spines and 8 ~ 9 soft strips on the ventral fin; There are 3 hard spines and 5 ~ 6 soft strips on the gluteal fin; 20 ~ 22 soft strips of caudal fin. The fin type of perch is d-I-13; A..Ⅲ-7 ~ 8; p . 15 ~ 18； Section five. The bass has two dorsal fins. The first dorsal fin consists of 12 hard spines without soft strips. The second dorsal fin includes 1 hard spines and 13 soft spines. There are 3 hard spines and 7 ~ 8 soft strips on the gluteal fin; Pectoral fin 15 ~ 18 soft strip; Abdominal fin 1 hard thorn and 5 soft strips. The movement of fish is closely related to the changes of body shape and fins, and its swimming power mainly depends on the following three ways:

Use the muscles of the trunk and tail to contract fluctuations.

The stroke movement of the swinging fin.

The fish can move forward by using the reaction force generated by spraying water backward from gill holes. Besides swimming, a few fish have a special form of exercise, that is, jumping or flying. For example, silver carp can jump out of the water obliquely and then fall vertically into the water. After the flying fish jumps out of the water, it can also open its wide pectoral fins, and it can fly up to about 300m in the air. Salmon can repeatedly jump over various obstacles in the river and migrate from the sea to the middle and upper reaches of the river to lay eggs. In addition, there are few fish that can crawl, such as? ? ? ? , bounce coating.

anal fin

Coordinate other fins to play a balancing role; If you lose it, your body will shake slightly.

Animal skin

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The skin of fish consists of epidermis and dermis. The epidermis is very thin and consists of several layers of epithelial cells and mucus layers. The epidermis is rich in unicellular mucus glands, which can continuously secrete viscous liquid and form a mucus layer on the body surface, which has lubricating and protective effects on fish, such as reducing skin friction resistance; Improve sports ability; Remove bacteria and dirt attached to fish. At the same time, it makes the body surface slippery and easy to avoid the enemy. Therefore, the epidermis is of great significance to the life and survival of fish. Below the epidermis is the dermis, which is rich in blood vessels, nerves, skin receptors and connective tissue, and there are pigment cells, luster cells and fat cells in the deep dermis and scales. There are three types of pigment cells: black, yellow and red. Melanocytes and yellow pigment cells exist in the skin of common fish. Red pigment cells mostly exist in the local skin of exotic tropical fish. Glorious cells contain guanosine crystals without pigment, which is highly reflective and makes fish appear silvery white. Some fish live in the depths of the ocean or in the dark water layer, and there is another skin derivative-luminescent gland cells, which can secrete phosphorus-rich substances and emit fluorescence after oxidation. ? ? ? Some species are.

There are many scales between epidermis and dermis, or in dermis. Fish scale is a unique skin derivative of fish, which is composed of calcium and covers the whole body or part (a certain part) of the fish surface. It can protect the fish from mechanical damage and external unfavorable factors, so it is called "exoskeleton". This is also one of the main characteristics of fish. The scales of existing fish can be divided into three types according to their appearance, structure and occurrence characteristics.

The meibomian is composed of dermis and epidermis, including the basal plate of dermis evolution and the dentate part on the plate, that is, the circular or diamond-shaped bony basal plate buried in dermis and the conical spine (tooth-shaped) protruding from epidermis with its pointed end facing backward and raised in the center. The surface of dentin is covered with enamel evolved from epidermis, and the center of dentin is pulp cavity. The whole medullary cavity is open at the bottom of the floor, and blood vessels and nerves penetrate into the cavity. Scales on the surface of sharks have the same occurrence and structure as teeth and should belong to homologous organs, so shark teeth are also called leathery teeth. The structure of fern scales is primitive and is found in cartilage scales.

Hard scales are rhombic bone scales evolved from dermis, with a layer of calcified hard scales on the surface and special light, which is called flash. Hard scales are the most primitive scales in teleost fishes, such as eels and sturgeons.

Bone scale is a round bone structure evolved from dermis. The front end is inserted into the scale capsule, and the back end is exposed to the skin in a free state, which is arranged in a composite tile shape. According to the shape of the free trailing edge, it can be divided into round scale and comb scale. The free trailing edge of round scales is smooth and blunt, which is common in lower teleost fishes, such as Cypriniformes and Silverfish. There are serrated protrusions on the trailing edge of comb scales, which are more common in high-grade fish such as Perciformes. Both round scales and comb scales have concentric rings on their surfaces, which are called annual rings. Like the annual rings of plant stems, the age, growth rate and breeding season of fish can be inferred from this.

The role of scale

As an external skeleton, fish scales can not only keep the fish in a certain shape, but also reduce the friction with water.

It provides a protective barrier for fish, isolating it from countless microorganisms around it, effectively avoiding infection and resisting diseases.

The scales in the belly of fish can reflect and refract bright light, just like a mirror, which dazzles the fierce aquatic animals below and produces a natural camouflage of not distinguishing things.

In addition, biologists judge the age of fish according to the rings on the scales (each ring represents a winter); It can also correctly grasp its growth, death and health status.

On both sides of fish's body, there are one or several lines that evolve from individual nests into tubes, which are called lateral line scales. Each lateral line scale has a lateral line hole, which can feel the low-frequency vibration of water. The scales of teleost usually identify species according to their number, size and arrangement. The arrangement of scales is usually expressed by a fractional formula, which is called scale type: for example, the scale type of crucian carp is 28-30, which means that the lateral scales of crucian carp are 28-30, the scales on the lateral lines are 5-6, and the scales under the lateral lines are 5-7.

Fish skeleton

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Zhu Xuanxian's Chinese painting "Furong Goldfish"

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Fishbone is divided into cartilage and hard bone according to its nature. Cartilaginous fish keep cartilage for life, because there is calcium precipitation in softness, it is also called calcified cartilage. The bones of teleost are mainly hard bones, which are divided into softened hard bones and periosteum according to different shapes: the hard bones formed by ossification on the cartilaginous primordia are softened hard bones, such as spine, ear bones and occipital bones; Hard bones formed by direct ossification of dermis and connective tissue are called membranous bones, such as frontal bone, parietal bone and branchial lid bone. Fish bones are divided into two parts according to different parts: axial bones and appendage bones.

Accessory skeleton

Appendages are divided into odd fin bones and lateral fin bones. The dorsal fin, gluteal fin and caudal fin bones in odd-numbered fins are all supported by the fin supporting bones (radial fin bones) inserted into muscles, and the fin supporting bones of teleost fish are also called fin supporting bones. The skeleton of the lateral fin consists of two parts: the skeleton with shoulder strap and waist bone and the fin bone (fin bone and fin strip). In fish, all appendages are not directly connected with the spine except the shoulder strap of teleost fish, which is one of the characteristics of fish, which is determined by the swimming mode of fish.

Divided into skull and spine

(1) has the largest number of skulls: the skulls of teleost fishes are composed of about 130 bone fragments (referring to existing fishes, ancient primitive fishes have as many as 180 skulls), which is the largest number of brain bones among vertebrates. The skull of fish is divided into two parts: skull and pharynx.

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Painter Li Zhenkai for more than a year (3 photos).

① The skull of cartilaginous fish is a cartilaginous cavity to protect the brain, with simple structure, no boundary and suture, and only the back of the skull is covered by a membrane. This kind of skull is called soft skull. The soft skull of cartilaginous fish is ossified into several occipital bones, ear bones, sphenoid bones, ethmoid bones, and membranous skull parts such as nasal bones, frontal bones, parietal bones and vomeroid bones, so the structure is very complicated. The skull of teleost is composed of many bone fragments, which constitute the main part of the skull. ② Vertebrates started from fish, the pharyngeal arch differentiated into upper and lower jaws, and the well formed the pharyngeal cranium. The pharyngeal cranium of fish is the most developed, with 7 pairs of ">"-shaped pharyngeal arches formed, and the first pair expanded into jaw arches. The posterior segment of the jaw arch is called palatal cartilage, and the abdominal segment is called Michael cartilage. They form the upper and lower jaws of cartilaginous fish. The appearance of the upper and lower jaws is more advanced than that of cirrhosis, and they can take the initiative to ingest food. However, teleost evolved into hard maxilla and maxilla, replacing cartilaginous maxilla (palatal cartilage), and Maxwell cartilage evolved into articular bone, odontoid bone and horn bone of cartilaginous hard bone. The second pair of lingual arches consists of bilateral lingual cartilages, angular lingual cartilages and central and basal lingual cartilages, which mainly support the tongue and also help to support the upper and lower jaws. The third to seventh pairs are branchial arches, which support gills and branchial septa.

(2) The spine replaces the notochord: The spine of fish is connected by many vertebrae into 1 columnar bone to replace part or all of the notochord, which has the functions of supporting the body and protecting the spinal cord and main blood vessels, and is more advanced than the round mouth. Fish's spine is characterized by inward depression on both sides, which is called biconcave vertebral body or biconcave vertebral body. It is unique to fish, and residual notochord can be seen in the gap between two adjacent vertebral bodies and in the tubule running through the vertebral bodies. Vertebrates started from fish, and the basic structure of the spine has been formed. The vertebrae of cartilaginous fish and teleost fish are divided into vertebral body, medullary arch, medullary spine, pulse arch and pulse spine. Among them, the vertebral body is the main part, and the ribs are connected with the transverse process of the spine, and the ribs of teleost fish are mostly developed.

digestive system