🦈How Do Fish Breathe?

Most fish can breathe underwater using their gills. In the breathing process, a large volume of water enters through the mouth and passes through the gills. These gills have comb-like feathery filaments that provide a large surface area to absorb oxygen from the water. After exchanging gases, water exits through gills openings. Note that some fish such as betta fish, and goldfish have a special breathing organ called labyrinth organ that allows them to breathe air and absorb oxygen.

How fish breathe?

Similar to other living organisms, fish also need oxygen for survival. We know that the fish can breathe under the water but have you ever wondered how fish breathe and get oxygen under the water?

Fish don’t have lungs as humans do but they have an interesting respiratory system that allows them to extract oxygen from the surrounding water. Let’s find out about the working of the respiratory system in fish.

Respiratory in fish

The respiratory system of fish is a network of organs and tissues that allows them to absorb oxygen from their surrounding water. The breathing process begins with water entering into the fish body through its mouth. This water then passes through curtains like feathery filaments of gills. These gill filaments have a network of blood vessels that absorb the oxygen from the water and get rid of carbon dioxide. This water with waste carbon dioxide exits the fish body through gill flaps and the oxygenated blood gets distributed throughout the body. This process of breathing requires fish to gulp a large volume of water so that a sufficient amount of oxygen gets absorbed in the blood vessels.

Breathing in Fish, Image credit: Cruithne9

Now, we know that how the respiratory system works in fish. Let’s dig into more details to learn how oxygen is absorbed in fish using gills.

Read: 🐠 Can Fish Drown?

How do gills work?

Gill is one of the most important organs in the fish because it allows them to breathe underwater. Gills are generally found just right behind the head. Each gill is supported by a cartilaginous or bony gill arch. Gills are composed of feathery filaments which have rows of plate‐like gill lamellae (comb-like structures). These gill lamellae provide a large surface area to exchange gases. In order to enhance the exchange of gases, these lamellae are positioned in a counter-current exchange system such that the flow of blood through the capillaries in the lamellae is counter-current to the flow of water.

Tuna Fish Gills (Image Credit: Chris 73 )

In bony fish (Osteichthyes), single gill opening on each side while some fish such as sharks, and rays have multiple gill openings. These gill slits allow the water with waste products such as carbon dioxide to exit the fish body. These gill slits also prevent the reverse flow of water from outside to inside. However, note that some amount of water gets absorbed through gill by the process of osmosis.

Read: 🐟 Can a fish survive in milk?

How do fish breathe under the ice?

Many fish can easily breathe and survive under the ice. In Arctic and Antarctic regions, only the top layer of the water reservoirs are frozen. Below this ice layer, water exists in the liquid state. With the help of gills, fish can easily breathe to absorb the dissolved oxygen from these surrounding liquid water. We also know that these water sources are oxygen-rich because cool water has more oxygen holding capacity than that of warm water.  

Can fish breathe air?

You must be thinking can fish breathe in air?

Well, the answer is no, fish cannot breathe in the air because fish don’t have lungs. However, note that there are some fish such as climbing perch (Anabas testudineus) that has both lungs and gills. These fish have air-breathing organs called the labyrinth organ. These labyrinth organs allow these fish to inhale air and absorb oxygen out of it. Climbing perch can survive out of water for about 5-6 days. These fishes migrate from one water source to another by moving on land using their fins. On dry land, they use lungs like us to breathe air. It is found that these fish can live up to six months in muddy conditions due to the presence of both gills and lungs. Therefore, climbing perch use gills to breathe oxygen in water while the lungs on dry land to absorb oxygen from the air. Gouramis, anabas, and betta fish are common examples of labyrinth fish.

Climbing Perch (Image credit: Xufanc)

How does a jellyfish breathe?

Jellyfish are not fish, they are invertebrates which absorb oxygen from surrounding water through membranes. Jellyfish don’t have dedicated organs for respiration or circulation. They have evolved such that they can absorb oxygen directly through the membranes present in the skin.

Read: 🐡 Do Fish Drink Water?

How do betta fish breathe?

Similar to most fish, betta fish also have gills to breathe underwater. However, note that they have a unique organ called a labyrinth that allows them to breathe air. The presence of gills as wells labyrinth organ allows betta fish to survive in low oxygen waters. They can easily survive out of water for a short period of time due to their labyrinth organ.

Betta Fish Labyrinth organ (Image credit: watershed3.tripod)

How do goldfish breathe?

Similar to betta fish, goldfish have both gills and labyrinth organ to breathe oxygen. Goldfish mainly use their gills to absorb oxygen. However, when the concentration of dissolved oxygen is poor in water, goldfish come to the water surface and gulps air to extract oxygen using the labyrinth organ.

Read: 🍣 Do Fish Have Blood?

How do eels breathe?

Similar to other fish, eels also have gills to breathe and absorb oxygen from the surrounding water. The surrounding water enters the fish body through the mouth and exits through gill openings. Before it exits from the gill slits, the oxygen from the water gets absorbed by the gill filaments into the blood vessels. Simultaneously, carbon dioxide from the blood capillaries diffuses with water.

Read more interesting questions about fish:

Professor Atom

View posts by Professor Atom
Professor Atom is a science enthusiast and alumni of IIT Bombay. According to him, every question can be solved with curiosity and mind mapping. ( Curiosity = Asking Questions = Learning )

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