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Fish Gills

Are you unaware of exactly what fish gills are? Well, then let us tell you, fish gills work as one of the most vital organs in the body of fish, which helps them to respire and stay alive. Unlike mammals, fish do not possess lungs for breathing. Instead, their lungs are replaced with gills, which can absorb dissolved oxygen into the body of fish from the water.

Most fish use their gills to exchange gases like O2 and CO2 to maintain a healthy respiratory cycle. Fish gills slits are typically made of tissues similar to short threads and protein structures. These tissues are known as filaments, which help fish to breathe appropriately.

Fish gills definition

Fish gills are the respiratory organ found in most aquatic creatures, which helps extract dissolved oxygen from the water and releases toxic carbon dioxide gas out of their body.

Fish gills are adapted explicitly for allowing respiration underwater to meet the daily survival needs of fish.

Fish gills function

The gills of fish species help in the extraction of dissolved oxygen from the water. Their gills contain many feather-like structures, known as filaments, which function in various ways to promote better respiration.

Gill filaments of fish help in transferring ions and water into their body. At the same time, it helps in exchanging carbon dioxide, oxygen, ammonia, and some acids. Each filament of fish gills contains a structure known as lamellae, supported with a vast capillary network. It provides a sufficient surface area on fish’s skin to exchange oxygen and carbon dioxide gases.

Gills, which are a crucial part of fish’s respiratory system, helps to exchange gases by absorbing water through it and pumping oxygen throughout their entire body. In some fish, the capillary blood tends to flow in the opposite direction to that of the water. It results in countercurrent exchange.

Fish gills also help push oxygen-deficit water out of their gill openings present on either side of their pharynx. Also, in some fish, gills work as the organ for urinating, which helps them to get rid of waste matters out of their body.

Do fish have gills?

Well, fish gills are one of the most vital organs without which these aquatic organisms cannot even survive. Fish are born in water and spend their entire life, swimming and living in the water. Thus, it becomes pretty tough for them to breathe underwater without gills.

For the very same reason, fish are not capable of breathing outside water. They do not have lungs, as this organ can only function with atmospheric air and not inside water. Hence, without gills, it is simply hard for any regular fish to live.

How many gills do fish have?

Now, how many gills a fish will have, that is entirely dependent on the fish species. Most bony species have their 5 pairs of gills; however, a few of them has already lost some due to evolution.

So, post-evolution, most modern fish possess 4 pairs of gills on both sides of their head. They have evolved four gills as it enables them to extract dissolved oxygen from the water efficiently.

Besides, some ocean fish, such as sharks, possess 5-7 pairs of gills, which help them maintain their large body’s natural respiratory cycle.

How do fish gills work?

Fish gills usually work by extracting dissolved oxygen out of water. It also lets the water carry away toxic carbon dioxide gas released due to respiration.

Fish tend to force water through their gills, where the water flows over many blood vessels. The oxygen molecules are extracted through the walls of those vessels and carried throughout the body to facilitate easy blood circulation. At the same time, waste carbon dioxide seeps out of the body through the gills.

Fish require a constant supply of oxygen for their survival. Hence, gills continuously work to ensure that fish get an adequate amount of oxygen passing through their body, which is necessary to prevent their suffocation underwater.

What is a complete gill called?

A complete gill in fish is called holobranch. A holobranch of fish comprises bony or cartilaginous arches.

Besides, the anterior and posterior part of this holobranch houses plate-like gill filaments, which form the entire respiratory system of fish.

How do fish gills extract oxygen from water?

Fish need oxygen to survive under the water. Thus, they are capable of absorbing dissolved oxygen from the water that lets them breathe easily. So, are you thinking, how do fish gills work? Well, to extract dissolved oxygen from water, fish rely on their sole respiratory organ, called ‘gills.’

Fish gills possess feathery structures, known as gill filaments, which are full of blood vessels. As they absorb water via the gill passages, it flows through the thin walls situated over their gills. The dissolved oxygen in the water gets extracted through it and moves into the blood, which helps circulate oxygen throughout their body. In this way, the gills of fish continuously extract oxygen out of the water to render a healthy and stable breathing cycle.

Do jellyfish have gills?

Though jellyfish have the word ‘fish’ in their name, they are not exactly fish. Thus, they do not possess similar organs like fish.

Fish are those species that are vertebrates and breathe through their gills. On the other hand, jellyfish are invertebrates. They do not require any fish gill to breathe underwater. Jellyfish are capable of absorbing oxygen from ocean water through their membranes.

Goldfish gills

Unlike mammals and similar to any other regular fish, goldfish use their gills for breathing. Their gills absorb dissolved oxygen from the water through the process of osmosis. The gills of goldfish are located behind their head and eyes on both sides of their body. The organ is covered and protected within the operculum.

As goldfish draws in oxygenated water through their mouth and closes their throat and operculum, their breathing begins. After that, the fish shuts their mouth and opens the operculum to enforce water through their gills.

The water passes through different parts of goldfish’ gills. But as the oxygenated water hits the gills rakers, it gets filtered thoroughly. The rakers catch free-floating food particles and other materials from the water and filter them out. Then the clean water passes through their gill arches and over the gill filaments.

The thin membranes present in the gill filaments facilitate a large surface area, which allows for a maximum amount of gas exchange. Then, finally, the dissolved oxygen gets extracted into the blood vessels to reach every body cell of the goldfish.

What is the difference between gills and lungs?

Fish gills are usually evaginations of the surface of their body. While some gills open directly to the aquatic environment, others stay enclosed inside a cavity. This respiratory organ is mainly found in fish. Also, frogs in their tadpole stage possess gills for breathing.

On the other hand, lungs are representative of invaginations of the body surface. The lungs present in a mammal’s body help them to breathe through atmospheric air. On the contrary, fish gills are specific for aquatic animals that cannot breathe in oxygen from the air but needs to extract dissolved oxygen from the water.

Can a fish breathe air?

Fish use their gills to take in oxygen underwater. Fish are not known for breathing in atmospheric air. Instead, picking up a fish and laying it down on the land to breathe air will simply make them collapse within a few seconds.

Even though the oxygen content in atmospheric air is higher than that present in the water of the same volume, it does not work for fish. Fish gills are habituated in extracting oxygen, which remains dissolved in the water. It helps them to have a continuous flow of oxygen through their respiratory system.

Though it is not so common for fish to breathe in the air, it is not impossible! Yes, you got that right; some exceptional fish species can breathe in oxygen from the atmospheric air.

Fish, such as mangrove rivulus, come with special adaptations, which let them breathe air. They have specialized skin with blood vessels present within a micron of their skin surface, allowing them to absorb more oxygen into their blood.

Are fish gills poisonous?

No, fish gills are not at all poisonous. Instead, fish gills are 100% edible. At the same time, eating fish gill does not have any harmful impact on the human body.


So, fish gills are one of the most vital organs present in fish’ bodies. It not only helps them to breathe easily underwater but also perform some other necessary functions, which are essential to survive marine life.

Hence, the gills of fish need to be highly functioning. If any of your aquarium fish contracts an infection in their gills, it is essential to facilitate quick treatment so that the fish can retain a healthy respiratory cycle.