Do Fish Have Hearts? A Guide to the Structure of a Fish's Heart
Fish are the oldest aquatic cold-blooded vertebrates that live in water and breathe through gills. They are found in the ocean and in freshwater, with two-thirds living in the ocean and the rest in freshwater. About 26,000 species of fish have been discovered and still exist in the world today. But many people believe fish do not have a heart. Is that really true? Let's take a look below and see whether fish actually have a heart!
Do fish have hearts?
Fish have hearts. Fish are the oldest vertebrates, and all vertebrates have a heart, but fish are the most primitive, with only one atrium and one ventricle, which serves to squeeze and promote blood circulation. A fish's heart is beside the gills, attached to the fish's neck, and each fish has only one heart. The heart of a fish has only 2 chambers, 1 atrium and 1 ventricle. The heart of a mammal has 4 chambers, 2 atria and 2 ventricles, and the heart of a bird also has 4 chambers. You can kill a live fish, and after cutting it open, slowly reach your middle finger toward the fish's throat, then slowly scoop back, and the fish's heart and other organs will come out. The location is in the abdominal cavity closest to the pectoral fins.
Do fish have ears?
Fish have ears. From the outside, fish seem to have no ears, and for a long time people thought fish could not hear anything, but fish do indeed have ears, and most fish have very good hearing. Fish have no eardrum. In fact, the ears of most fish do not connect with the outside world, but are protected in sacs on both sides of the head, located just behind the eyes. Sound travels through water much more easily than through air. Like other animals, a fish's body contains a large amount of water, and sound can pass directly through the fish's body and reach the ears.
Many kinds of fish can collect sound in another way. The ears are connected to the swim bladder. Sounds in the water make the wall of the swim bladder vibrate, just as sound passing through air makes the eardrum vibrate. This vibration is then usually transmitted to the ears along a series of small bones connected to the swim bladder. Some fish do not rely on small bones to transmit vibrations, but instead rely on a tubular organ extending from the swim bladder. Sound is very important to fish. Many fish can make powerful calls to each other that can be heard several kilometers away. Some fish make sounds by grinding their teeth, others by rubbing their fins against their bodies, and many fish use the swim bladder to make and distinguish sounds. Some specially can strike muscles to vibrate the swim bladder and produce sound.
How long can fish live?
Generally speaking, the lifespan of fish is related to their individual size and the age at sexual maturity. The larger the fish, the later it reaches sexual maturity, and the longer its lifespan. From this perspective, the largest fish in the world——the whale——should have the longest lifespan. Unfortunately, so far people know nothing about its lifespan. According to reports, the beluga sturgeon living in the Caspian Sea and the Black Sea can weigh up to 1,500 kilograms and live more than 100 years. The Chinese paddlefish in China's Yangtze River also has a lifespan close to 100 years. Many small fish, such as the freshwater goby, the black carp, and the icefish, live only about one year.
Although the lifespans of fish vary greatly among species, the lifespans of the vast majority of fish are concentrated between 2 and 20 years, of which 60% are concentrated between 5 and 20 years. Fish that can live more than 30 years account for no more than 10%, while those living less than 2 years account for only 5%. Among China's freshwater fish, the silver razor belly fish, the hemiculter, the redfin culter, the copper fish, the yellow catfish, the silver xenocypris, and the snakehead gudgeon have lifespans between 2 and 4 years. Black carp, grass carp, silver carp, bighead carp, crucian carp, bream, topmouth culter, and mandarin fish mostly live 7 to 8 years, and a few can live more than 10 years. Saltwater fish have somewhat shorter lifespans.
In addition, the same species of fish living in different environments also differs in lifespan. For example, the large yellow croaker can live 29 years along the coast of Zhejiang, while along the coasts of Fujian and Guangdong it usually lives only 17 years, and in the waters east of Hainan it lives only 9 years.
The special abilities of fish
1. Flying fish: The flying fish has an elongated, flat, rounded body that is slightly spindle-shaped. It generally has a body length of 20 to 30 cm and a weight of 400 to 1,500 grams. Its back is quite wide, its sides are relatively flat and gradually taper toward the tail, and its belly is very narrow. The head is short, the snout is short, the eyes are large, and the mouth is small. The teeth are fine, and the upper and lower jaws form narrow bands. There is one dorsal fin at the rear of the body opposite the anal fin. The pectoral fins are particularly long and broad and can reach the end of the anal fin. The pelvic fins are large, positioned posteriorly, and can reach the end of the anal fin. The two fins spread out like dragonfly wings.
2. Sound-producing fish: The conger eel can emit a “barking” sound, the electric catfish's call is like an angry cat, the boxfish can make a dog-like bark, and the gurnard's call sometimes sounds like a pig, sometimes like a groan, and sometimes like snoring. The seahorse makes a monotonous drum-like sound. Sciaenid fish are famous for being good at calling, and their sounds resemble rolling, drumming, the flight sound of a hummingbird, cat meows, and whistles. Their calls are especially common during the reproductive period, with the purpose of gathering in groups.
3. Electricity-generating fish: Some fish can generate electricity with their bodies, and the voltage they release is actually several times greater than the voltage of the electricity we use in daily life. There are about 500 species of fish with the ability to generate electricity, such as the electric eel, electric catfish, electric eel, and electric ray, and the current strength and voltage produced by various electricity-generating fish differ. The electric ray has a flat, round body with a long tail, looking just like a round fan. The electric catfish living in Africa's Nile River is only 1 meter long but can emit high-voltage electricity of 350 volts.
4. Glowing fish: Some fish glow. For example, the hairtail and the Bombay duck along the southeastern coast of China emit light produced by luminous bacteria attached to their bodies, while more fish glow with light produced by the fish's own luminous organs. The lanternfish has multiple rows of light organs on its belly and sides, like rows of candles, hence the name lanternfish. The deep-sea headlight fish has a flat back of the head covered by a pair of very large light organs, and this large light organ may serve a visual function.
5. Walking fish: The climbing perch inhabits still waters with slow currents and a lot of mud. When the water dries up or the environment becomes unsuitable, it often relies on swinging its gill covers, pectoral fins, and turning over to climb over embankments and slopes, move to new waters, or hide in the mud. The climbing perch has highly developed suprabranchial organs and can breathe air, so it can survive out of water for a long time, and it can live for quite a long time when the water is lacking oxygen, when it is out of water, or in slightly moist soil. The climbing perch feeds on small fish, small shrimp, zooplankton, insects, and their larvae.
6. Drowning fish: Drowning fish? Although this sounds absurd, it is a fact. The swim bladder is the fish's “life buoy” when swimming, and it can regulate the fish's specific gravity by inflating and deflating. In this way, when the fish swims, it needs only minimal muscle activity to maintain a stable state in the water without sinking or floating. However, after a fish sinks to a certain depth, the huge external pressure makes it unable to adjust the volume of the swim bladder anymore. At this point, the buoyancy it receives is less than its own gravity, so it involuntarily sinks toward the bottom, can no longer float up, and eventually drowns because it cannot breathe.