Does fish have a heart?

Fish are the oldest cold-blooded aquatic vertebrates living in water. They breathe through their gills and are distributed in the ocean and fresh water. 2/3 of them live in the ocean, and the rest live in fresh water. About 26000 species of fish have been found in the world. But many people think that fish have no heart. Is that really the case? Now let's take a look at whether the fish have a heart or not.

Does fish have a heart?

Fish have a heart. Fish is the oldest vertebrate, vertebrates have a heart, but fish is the lowest, only one atrium, one ventricle, play the role of squeezing to promote blood circulation. The heart of the fish is next to the gills and attached to the neck of the fish. Each fish has only one heart. The heart of a fish has only two chambers, one atrium and one ventricle. The heart of mammals has four chambers, two atriums and two ventricles, and the hearts of birds also have four chambers. You can kill a live fish, slowly reach the fish's throat with your middle finger, then dig back slowly, and the fish's heart and other organs will come out in the abdominal cavity closest to the pectoral fin.

Do fish have ears?

Fish have ears. From the outside, fish seem to have no ears. for a long time, people thought that fish could not hear anything, but fish do have ears, and most fish have good hearing. Fish do not have a tympanic membrane. In fact, the ears of most fish are not connected to the outside world, but are protected in the sacs on both sides of the head, just behind the eyes. Sound travels much more easily in water than in air. Like other animals, fish have a lot of water in their bodies, and sound can pass directly through the fish's body and reach the ears.

Many species of fish can collect sound in another way, with the ear connected to the swim bladder, and the sound in the water vibrates the wall of the bladder, just as the sound vibrates the tympanic membrane through the air, and then the vibration is usually transmitted to the ear along a string of small bones connected to the swim bladder. Some fish do not rely on small bones to transmit vibration, but on tubular organs that extend from the swim bladder. Sound is very important to fish. Many fish can make powerful calls to each other, which can be heard a few kilometers away. Some fish make sound by grinding their teeth, others make sound by rubbing their fins on their bodies, and many fish distinguish sound with fish. Special fish can knock on the swim bladder to make a sound.

How long can the fish live?

Generally speaking, the lifespan of fish is related to its individual size and the age of sexual maturity. The larger the fish, the later the sexual maturity and the longer the life span. From this point of view, the whale, the largest fish in the world, should have the longest life span. Unfortunately, so far, people know nothing about its lifespan. It is reported that Europe, which lives in the Caspian Sea and the Black Sea, weighs up to 1500 kilograms and lives longer than 100 years. The life span of the White Sturgeon in the Yangtze River in China is also close to 100 years. Many small fish, such as fake tiger fish, herring, silverfish and so on, live only about a year.

Although the lifespan of fish varies greatly from species to species, the lifespan of most fish is between 2 to 20 years, and 60% of them are concentrated in 5 to 20 years. Fish that can live for more than 30 years will not exceed 10%, and only 5% of fish can live for less than 2 years. Among the freshwater fish in China, the life span of silver floating fish, minnow, red fin fish, copper fish, yellow catfish, silver fish and snakehead is between 2 and 4 years. The life span of herring, grass carp, silver carp, bighead carp, crucian carp, carp, warped mouth red fish and mandarin fish is more than 7 to 8 years, and some of them can live to more than 10 years, while the life span of marine fish is shorter.

In addition, the same kind of fish live in different environments, and their lifespan is also different. For example, Pseudosciaena Crocea can live for 29 years along the coast of Zhejiang, but only 17 years along the coast of Fujian and Guangdong, and only 9 years in the eastern sea area of Hainan.

The special function of fish

1. Flying fish: swallow rays have a long, flat, round body and are slightly fusiform. The average body length is 20 to 30 centimeters and the weight is 400 to 1500 grams. The back is quite wide, the sides are flat to the tail tapering, and the ventral side is very narrow. The head is short, the kiss is short, the eye is big, the mouth is small. The teeth are fine and the upper and lower jaws are in a narrow band. The dorsal fin is opposite to the anal fin at the back of the body. The pectoral fin is very long and wide, reaching the end of the anal fin, large ventral fin and posterior position, reaching the end of the anal fin. The fins stretch like the wings of a dragonfly.

2. Vocal fish: the Kangji carp will make a "barking" sound, the electric catfish's cry is like the wrath of a cat, the cuttlefish can make a dog's cry, and the squealing of the gills is sometimes like a pig's cry, sometimes like a moan, sometimes like a snore, and the seahorse gives a monotonous sound like a drum. The stone head fish is famous for its sound, such as rolling, drumming, the flying sound of hummingbirds, cats and whistles, which are especially common during reproduction for the purpose of clustering.

3. Fish that generate electricity: the bodies of some fish can generate electricity, and the voltage they emit is several times higher than that of our daily life. There are about 500 kinds of fish with power generation capacity, such as electric eel, electric catfish, electric eel, electric ray and so on. The electric ray has a flat and orchid body, with a long tail, like a ball fan. The electric catfish, which lives in the Nile in Africa, is only 1 meter long, but it can emit a high voltage of 350 volts.

4. Luminous fish: some fish emit light, such as the hairtail and faucet fish along the southeast coast of China, which are emitted by the light-emitting bacteria attached to the body, while more fish emit light from the luminous organs of the fish themselves. Candlelight fish its abdomen and ventral side have multiple lines of light, like rows of candles, hence the name candlelight fish deep-sea bald fish head flat, covered by a pair of large light emitters, the large light emitter may play a visual role.

5. Walking fish: the turtle shell climbing perch lives in a still, slow-flowing, muddy body of water. When the water body dries up or the environment is not suitable, often rely on swinging the Gill cover, pectoral fin, turning over and other methods to climb over the embankment, slope, move to new waters, or lurking in the mud. The suprabranchial apparatus of the turtle shell climbing perch is very developed and can breathe air, so it can stay away from the water for a long time and can live for a long time when the water body is anoxic, out of water, or in slightly moist soil. Turtle shell climbing perch feeds on small fish, shrimp, zooplankton, insects and their larvae.

Drowned fish: drowned fish? Ridiculous as it sounds, it is true. Swim bladder is the "lifebuoy" of fish swimming, which can adjust the specific gravity of fish by inflating and deflating. In this way, fish need only the least muscle activity when swimming, so that they can maintain a steady state of not sinking or floating in the water. However, when the fish sinks to a certain depth, the great pressure from the outside will make it unable to adjust the volume of the swim bladder, so the buoyancy is less than its own gravity, so it can't help but sink to the bottom and can't float any more. and eventually drowned because he couldn't breathe.