Do fish have hearts?

In this brief guide, we’ll address the search query: “Do fish have hearts?” Also, we’ll explore what the parts of a fish are, how fish can be divided, what animals don’t have hearts, and what animals have several hearts. 

Do fish have hearts? 

Yes, fish have hearts. Fish have closed circulatory systems. This means that their organs are irrigated with blood which transports oxygen to their tissues and organs. The heart pumps blood that circulates through blood vessels, to the lungs or gills, where gas exchange occurs, and at the same time pumps oxygenated blood to other parts of the body. 

Notably, fish have a heart that is made of two chambers one of which is an atrium and the other which is a ventricle. 

The atrium collects blood that has supplied organs and other tissues with oxygen. The ventricle redirects this blood towards the gills, where it will acquire oxygen pumped through the body and repeat the process of oxygenating organs and tissues. 

Some other types of animals (insects, mollusks, crustaceans) may have open circulatory systems (no blood vessels but they too require organs (hearts) to pump their blood throughout their bodies.  

Few animals don’t have hearts or circulatory systems for that matter. These include sponges, jellyfish, and more primitive animal life forms. They source oxygen, nutrients, and other substances necessary for their survival via diffusion which means they absorb and filter out.

What are the parts of a fish?

Externally, the parts of a fish are the mouth, the eyes, nares (nostrils), and the body, along which the fins are inserted. Fish have a pair of pectoral fins, pelvic fins, an anal fin, dorsal fins, and one long fin at the end of their tails. 

Of course, these fins can vary between groups of fish but they all serve the purpose of allowing fish to steer their direction while swimming, be it with the help of muscles, or a swim bladder. 

Internally, the parts of a fish are the brain, heart, liver, gills, gall bladder, a spine, kidneys, a spleen, stomach, bowels (intestines), reproductive organs, urinary bladder, and vent (which serves as a cloaca).

Depending on the fish’s taxonomical group, a fish may have bones or cartilage, or vertebrate-like segments. 

How can fish be divided? 

Fish can be divided into five groups, which are lampreys, hagfish, cartilaginous fish, ray-finned fish, and lobe-finned fish. 

Lampreys and hagfish lack jaws and resemble eels, though lampreys have circular mouths lined with teeth, and hagfish produce slime as a defense mechanism. 

Cartilaginous fish are sharks and rays, and these lack bones, though they achieve movement through the motion of powerful muscles that are attached to their cartilage structures.

Ray-finned fish – are species of fish that have fins with long, webbed fins that have no digits. These fish have swim bladders that they use to propel themselves through water and include many types such as tuna, sturgeon, salmon, etc. 

Lobe-finned fish allude to living fossils such as coelacanths and lungfish. These fish are considered to be the divergence point between fish and other vertebrates such as amphibians and reptiles. Their fins are fleshy appendages with short fins attached to their ends. 

What animals don’t have hearts? 

Animals that don’t have hearts include sea sponges and jellyfishes, flatworms, corals, starfish, sea cucumbers, sea lilies, and sea anemones, to name a few. 

This is because they have no circulatory systems. They acquire their oxygen by diffusion, which can be done by absorbing water or using special hair-like structures to trap bubbles of oxygen that are dissolved in water. 

These are among the more primitive forms within the animal kingdom, as they lack blood, a body cavity with vital organs, and other traits of animals. 

What animals have several hearts? 

Many animals have several hearts. Hearts are internal organs that pump oxygenated blood into tissues and cavities while pushing blood toward organs such as gills and other gas-exchange mechanisms, such as spiracles. 

Notably, worms (annelids), insects, mollusks, hagfish, and other animals with open circulatory systems have several hearts. 


In this brief guide, we’ve addressed the search query: “Do fish have hearts?” Also, we’ve explored what the parts of a fish are, how fish can be divided, what animals don’t have hearts, and what animals have several hearts. 


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