This is common in stagnant and acidic water bodies where dissolved oxygen concentrations are very low or the acidity of the water causes problems for gills. Other aquatic animals such as dolphins, whales and seals do not have gills but that it because they are not fish at all, they are mammals.
Marine mammals have evolved from land-based animals but have moved back into aquatic environments. Whales and dolphins are in fact more closely related to the hippopotamus than any other living animal. The respiratory gills of fishes are most likely to have evolved from the food collecting contraptions of more primitive animals. Fish belong to the phylum Chordata, as do mammals and all other vertebrate animals. The most primitive Chordates however are invertebrates that use tiny growths called cilia to filter food from the water much in the same way as fish absorb oxygen from water.
This evolution from food filtering to oxygen absorption evolved a very long time ago. Fish were the first vertebrates to evolve and did so way back in during the Early Cambrian around million years ago. One of the earliest known fishes to possess gills is an extremely primitive fish called Myllokunmingia and was found in shallows water in Asia.
Although gills were important for the evolution of fish, it was the evolution of the jaw bone that really allowed the explosion of fish diversity into the 60, species that are currently present on Earth. This is the resource that I recommend above anything else for aspiring biologists. The latest edition is available from Amazon and the Book Depository. Learn about animals, plants, evolution, the tree of life, ecology, cells, genetics, fields of biology and more.
A confirmation email has been sent to the email address that you just provided. Check your emails and make sure you click the link to get started on our 6-week course. Basic Biology: An Introduction. Also available from Amazon , Book Depository and all other good bookstores. Know the answer? Why not test yourself with our quick 20 question quiz. Fish Gills Fish breathe through gills instead of lungs.
Gill structure Each gill is supported by a gill arch — a bony structure that is oriented vertically on the side of a fish, just behind its head. How do gills work? Do all fishes have gills?
How and when did gills evolve? Last edited: 18 July Want to learn more? There was an error submitting your subscription. Please try again. Also, in some fishes, gills work as the organ for urinating, which helps them to get rid of waste matters out of their body.
Well, fish gills are one of the most vital organs without which these aquatic organisms cannot even survive. Fishes 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, fishes 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. 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 fishes 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. 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.
Fishes 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. Fishes require a constant supply of oxygen for their survival. Hence, gills continuously work to ensure that fishes get an adequate amount of oxygen passing through their body, which is necessary to prevent their suffocation underwater. 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 fishes.
Fishes 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? 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 fishes continuously extract oxygen out of the water to render a healthy and stable breathing cycle. Thus, they do not possess similar organs like fish.
Fishes are those species that are vertebrates and breathe through their gills. On the other hand, jellyfishes are invertebrates. They do not require any fish gill to breathe underwater. Jellyfishes are capable of absorbing oxygen from ocean water through their membranes. Unlike mammals and similar to any other regular fish, goldfishes 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.
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.
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 fishes.
Also, frogs in their tadpole stage possess gills for breathing. On the other hand, lungs are representative of invaginations of the body surface.
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. Fishes use their gills to take in oxygen underwater.
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