Fish cannot breathe air using their gills because gills are adapted to extract oxygen from water, not air.

Gillis, A. and Tidswell, O. (2017). "Evolutiom: Origin of vertebrate gills". Nature. 542 (7642): 394. Bibcode: 2017Natur.542Q.394.. doi: 10.1038/542394a. PMID 28230134. {{ cite journal}}: CS1 maint: multiple names: authors list ( link) Pozdnyakov, S. E. & Gibson, D. I. (2008). Family Didymozoidae Monticelli, 1888. In R. A. Bray, D. I. Gibson & A. Jones (Eds.), Keys to the Trematoda, Vol. 3 (pp. 631-734). London: CAB International and The Natural History Museum. The primary lamellae are attached to the gill arch, while the secondary lamellae are attached to the primary lamellae.Gills are made up of many thin, delicate filaments called lamellae. These lamellae are highly vascularized, meaning they have a rich blood supply. The structure of the gills allows for efficient oxygen extraction through countercurrent exchange.

In bony fish, the gills lie in a branchial chamber covered by a bony operculum ( branchia is an Ancient Greek word for gills). The great majority of bony fish species have five pairs of gills, although a few have lost some over the course of evolution. The operculum can be important in adjusting the pressure of water inside of the pharynx to allow proper ventilation of the gills, so that bony fish do not have to rely on ram ventilation (and hence near constant motion) to breathe. Valves inside the mouth keep the water from escaping. [7] Graham, Anthony; Richardson, Jo (2012). "Developmental and evolutionary origins of the pharyngeal apparatus". EvoDevo. Springer Science and Business Media LLC. 3 (1): 24. doi: 10.1186/2041-9139-3-24. ISSN 2041-9139. PMC 3564725. PMID 23020903. Some species, such as the great white shark, are capable of shutting off blood flow to certain gill arches to conserve energy during periods of low oxygen availability. Tuna Gills are located on either side of the fish’s head, protected by a bony structure called the gill arch. The gill arch supports the gill filaments, which are made up of primary and secondary lamellae. Gills are highly efficient at extracting oxygen from water, but they are not effective at extracting oxygen from air.Gills and lungs both function to extract oxygen from the environment and deliver it to the bloodstream. However, gills are adapted to extract oxygen from water, while lungs are adapted to extract oxygen from air. A high surface area is crucial to the gas exchange of aquatic organisms, as water contains only a small fraction of the dissolved oxygen than air does, and it diffuses more slowly. A cubic meter of air contains about 250 grams of oxygen at STP. [ dubious – discuss] [ citation needed] In fresh water, the dissolved oxygen content is approximately 8cm 3/L compared to that of air which is 210cm 3/L. [4] Water is 777 times more dense than air and is 100 times more viscous. [4] Oxygen has a diffusion rate in air 10,000 times greater than in water. [4] The use of sac-like lungs to remove oxygen from water would not be efficient enough to sustain life. [4] Rather than using lungs, "[g]aseous exchange takes place across the surface of highly vascularised gills over which a one-way current of water is kept flowing by a specialised pumping mechanism. The density of the water prevents the gills from collapsing and lying on top of each other, which is what happens when a fish is taken out of water." [4] Laurin M. (1998): The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I-systematics, middle ear evolution, and jaw suspension. Annales des Sciences Naturelles, Zoologie, Paris, 13e Série 19: pp 1-42.

Fish extract oxygen from water by passing it over their gills. The gills are highly vascularized structures that contain thin, delicate filaments called lamellae. Gills and lungs are both respiratory organs that allow animals to extract oxygen from the air or water and release carbon dioxide. Lungs, on the other hand, are specialized organs that are adapted for extracting oxygen from air. They are made up of a network of air sacs and tubes that are lined with thin, moist membranes. As water flows over the lamellae, oxygen diffuses from the water into the bloodstream of the fish, while carbon dioxide diffuses from the bloodstream into the water. What are the different types of gills found in aquatic animals? However, some species have unique adaptations to their gills that allow them to survive in extreme environments. Here are some special cases of respiration in fish: Sharks and RaysWater is the medium that carries oxygen to the gills, and the concentration of dissolved oxygen in water is crucial for the survival of fish. Hypoxic zones, or areas with low dissolved oxygen, can cause stress and even death in fish. Gills are specialized organs that allow aquatic animals to extract oxygen from the water. The evolution of gills has played a crucial role in the adaptation of aquatic species to their environment. However, these gills are reabsorbed before birth, and the animals rely on lungs for respiration after birth. The Process of Respiration in Gills Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely. Gills are an essential organ for fish, allowing them to extract oxygen from water and release carbon dioxide. However, the efficiency of gills is highly dependent on the surrounding environment.

Fish gills are organs that allow fish to breathe underwater. Most fish exchange gases like oxygen and carbon dioxide using gills that are protected under gill covers (operculum) on both sides of the pharynx (throat). Gills are tissues that are like short threads, protein structures called filaments. These filaments have many functions including the transfer of ions and water, as well as the exchange of oxygen, carbon dioxide, acids and ammonia. [1] [2] Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide. When in water, lungfish use their gills to extract oxygen. However, when on land, they rely on a specialized lung that allows them to breathe air.Although most fish respire primarily using gills, some fish can at least partially respire using mechanisms that do not require gills. In some species cutaneous respiration accounts for 5 to 40 per cent of the total respiration, depending on temperature. Cutaneous respiration is more important in species that breathe air, such as mudskippers and reedfish, and in such species can account for nearly half the total respiration. [16] I do hope that continued research will prove that some psychoactive substances such as marijuana, magic mushrooms and ketamine are more helpful in treating depression and anxiety than the anti-depressants that are currently available from the NHS. Fish from multiple groups can live out of the water for extended time periods. Amphibious fish such as the mudskipper can live and move about on land for up to several days, or live in stagnant or otherwise oxygen depleted water. Many such fish can breathe air via a variety of mechanisms. The skin of anguillid eels may absorb oxygen directly. The buccal cavity of the electric eel may breathe air. Catfish of the families Loricariidae, Callichthyidae, and Scoloplacidae absorb air through their digestive tracts. [4] Lungfish, with the exception of the Australian lungfish, and bichirs have paired lungs similar to those of tetrapods and must surface to gulp fresh air through the mouth and pass spent air out through the gills. Gar and bowfin have a vascularized swim bladder that functions in the same way. Loaches, trahiras, and many catfish breathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (such as gouramis and bettas) have a labyrinth organ above the gills that performs this function. A few other fish have structures resembling labyrinth organs in form and function, most notably snakeheads, pikeheads, and the Clariidae catfish family. I just watched it and will echo the comments made by others in thanking Matt for his bravery and honesty in making the video. I hope that making and sharing the video has not only helped him but also helped others. Justine, JL. (September 2004). "Three new species of Huffmanela Moravec, 1987 (Nematoda: Trichosomoididae) from the gills of marine fish off New Caledonia". Systematic Parasitology. 59 (1): 29–37. doi: 10.1023/B:SYPA.0000038442.25230.8b. PMID 15318018. S2CID 29105973.