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145-517: Global demand is increasing for dietary fish protein , which has resulted in widespread overfishing in wild fisheries , resulting in significant decrease in fish stocks and even complete depletion in some regions. Fish farming allows establishment of artificial fish colonies that are provided with sufficient feeding , protection from natural predators and competitive threats , access to veterinarian service, and easier harvesting when needed, while being separate from and thus do not usually impact

290-583: A cascade method, Swiss chemist and physicist Raoul Pierre Pictet evaporated liquid sulfur dioxide in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877, to the French Academy of Sciences in Paris announcing his discovery of liquid oxygen . Just two days later, French physicist Louis Paul Cailletet announced his own method of liquefying molecular oxygen. Only

435-535: A 2-acre (8,100 m) area.). However, fish tend also to be animals that aggregate into large schools at high density. Most successful aquaculture species are schooling species, which do not have social problems at high density. Aquaculturists feel that operating a rearing system above its design capacity or above the social density limit of the fish will result in decreased growth rate and increased feed conversion ratio (kg dry feed/kg of fish produced), which results in increased cost and risk of health problems along with

580-477: A chemical element. The name oxygen was coined in 1777 by Antoine Lavoisier , who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion. Common industrial uses of oxygen include production of steel , plastics and textiles , brazing, welding and cutting of steels and other metals , rocket propellant , oxygen therapy , and life support systems in aircraft , submarines , spaceflight and diving . One of

725-402: A clinical nutrition approach using functional feeds could potentially move away from chemotherapeutic and antibiotic treatments, which could lower the costs of disease treatment and management in fish farms. In this investigation three fishmeal-based diets were served—one made of 31% lipid and the other two made of 18% lipid (one contained fishmeal and the other krill meal. Results demonstrated

870-470: A combination of many other factors, including reduced wastage , better utilization, improved distribution channels and growing consumer demand , linked with population growth, rising disposable incomes and urbanization . Europe , Japan and the United States of America together accounted for 47 percent of the world's total food fish consumption in 1961, but only about 20 percent in 2015. Of

1015-590: A common natural occurrence. Though not a health concern in thoroughly cooked fish, parasites are a concern when consumers eat raw or lightly preserved fish such as sashimi , sushi , ceviche and gravlax . The popularity of such raw fish dishes makes it important for consumers to be aware of this risk. Raw fish should be frozen to an internal temperature of −20 °C (−4 °F) for at least 7 days to kill parasites; home freezers may not be cold enough. Historically, fish that live all or part of their lives in fresh water were considered unsuitable for sashimi due to

1160-496: A controversial one. Many cultured fishes (tilapia, carp, catfish, many others) can be raised on a strictly herbivorous diet. Top-level carnivores (most salmonidae species in particular) on the other hand, depend on fish feed, of which a large portion is usually derived from wild-caught fish ( anchovies , menhaden , etc.). Vegetable-derived proteins have successfully replaced fish meal in feeds for carnivorous fishes, but vegetable-derived oils have not successfully been incorporated into

1305-478: A decrease in profits. Stressing the animals is not desirable, but the concept of and measurement of stress must be viewed from the perspective of the animal using the scientific method. Sea lice , particularly Lepeophtheirus salmonis and various Caligus species, including C. clemensi and C. rogercresseyi , can cause deadly infestations of both farm-grown and wild salmon. Sea lice are ectoparasites which feed on mucus, blood, and skin, and migrate and latch onto

1450-434: A few drops of the liquid were produced in each case and no meaningful analysis could be conducted. Oxygen was liquefied in a stable state for the first time on March 29, 1883, by Polish scientists from Jagiellonian University , Zygmunt Wróblewski and Karol Olszewski . In 1891 Scottish chemist James Dewar was able to produce enough liquid oxygen for study. The first commercially viable process for producing liquid oxygen

1595-551: A food containing dried Schizochytrium in place of fish oil . When compared to a control group raised on regular food, they exhibited higher weight gain and better food-to-growth conversion, plus their flesh was higher in healthy omega-3 fatty acids . Within intensive and extensive aquaculture methods, numerous specific types of fish farms are used; each has benefits and applications unique to its design. Fish cages are placed in lakes, bayous, ponds, rivers, or oceans to contain and protect fish until they can be harvested. The method

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1740-420: A greenhouse. A hydroponic bed is placed near, above or between them. When tilapia are raised in the tanks, they are able to eat algae, which naturally grow in the tanks when the tanks are properly fertilized. The tank water is slowly circulated to the hydroponic beds, where the tilapia waste feeds commercial plant crops. Carefully cultured microorganisms in the hydroponic bed convert ammonia to nitrates , and

1885-546: A licensed fugu chef who has passed the national examination in Japan. Ciguatera poisoning can occur from eating larger fish from warm tropical waters, such as sea bass , grouper , barracuda and red snapper . Scombroid poisoning can result from eating large oily fish which have sat around for too long before being refrigerated or frozen. This includes scombroids such as tuna and mackerel , but can also include non-scombroids such as mahi-mahi and amberjack . The poison

2030-481: A light sky-blue color caused by absorption in the red (in contrast with the blue color of the sky, which is due to Rayleigh scattering of blue light). High-purity liquid O 2 is usually obtained by the fractional distillation of liquefied air. Liquid oxygen may also be condensed from air using liquid nitrogen as a coolant. Liquid oxygen is a highly reactive substance and must be segregated from combustible materials. The spectroscopy of molecular oxygen

2175-564: A major role in absorbing energy from singlet oxygen and converting it to the unexcited ground state before it can cause harm to tissues. The common allotrope of elemental oxygen on Earth is called dioxygen , O 2 , the major part of the Earth's atmospheric oxygen (see Occurrence ). O 2 has a bond length of 121  pm and a bond energy of 498  kJ/mol . O 2 is used by complex forms of life, such as animals, in cellular respiration . Other aspects of O 2 are covered in

2320-595: A microscope) (see Leviticus 11:10–13 ). Sunni Muslim laws are more flexible in this and catfish and shark are generally seen as halal as they are special types of fish. Eel is generally considered permissible in the four Sunni madh'hab , but the Ja'fari jurisprudence followed by most Shia Muslims forbids it. Many tribes of the Southwestern United States , including the Navaho , Apache , and Zuñi , have

2465-438: A part of air that he called spiritus nitroaereus . In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects. From this, he surmised that nitroaereus is consumed in both respiration and combustion. Mayow observed that antimony increased in weight when heated, and inferred that

2610-404: A process called eutrophication and the decay of these organisms and other biomaterials may reduce the O 2 content in eutrophic water bodies. Scientists assess this aspect of water quality by measuring the water's biochemical oxygen demand , or the amount of O 2 needed to restore it to a normal concentration. Paleoclimatologists measure the ratio of oxygen-18 and oxygen-16 in

2755-644: A prominent part in keeping the tilapia healthy with recirculated water. A number of large, well-capitalized ventures in this area have failed. Managing both the biology and markets is complicated. One future development is the combination of integrated recycling systems with urban farming as tried in Sweden by the Greenfish Initiative . This is also called a "flow through system" . Trout and other sport fish are often raised from eggs to fry or fingerlings and then trucked to streams and released. Normally,

2900-524: A record 82.1 million tonnes in 2018. Farming carnivorous fish such as salmon , however, does not always reduce pressure on wild fisheries, such farmed fish are usually fed fishmeal and fish oil extracted from wild forage fish . The 2008 global returns for fish farming recorded by the FAO totaled 33.8 million tonnes worth about US$ 60 billion. Although fish farming for food is the most widespread, another major fish farming industry provides living fish for

3045-424: A result of its high fat content, contain a range of fat-soluble vitamins (A, D, E and K) and essential fatty acids, all of which are vital for the healthy functioning of the body." Eating oily fish containing long-chain omega-3 fatty acids may reduce systemic inflammation and lower the risk of cardiovascular disease . Eating about 140 grams (4.9 oz) of oily fish rich in omega-3 fatty acids once per week

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3190-465: A result, the food available in all the parts of the pond is used. Fish used in this system include catla and silver carp (surface feeders), rohu (a column feeder), and mrigal and common carp (bottom feeders). Other fish also feed on the excreta of the common carp, and this helps contribute to the efficiency of the system which in optimal conditions produces 3000–6000 kg of fish per hectare per year. One problem with such composite fish culture

3335-422: A series of mesh-wire frames and nets. It is designed to disperse wastes better than more conventional farms in sheltered coastal waters, therefore supporting higher fish packing density. Recently, copper alloys have become important netting materials in aquaculture . Copper alloys are antimicrobial , that is, they destroy bacteria , viruses , fungi , algae , and other microbes . In the marine environment ,

3480-426: A significant difference in the immune and inflammatory responses and pathology in heart tissue as the fish were infected with PMCV. Fish fed with functional feeds with low lipid content demonstrated milder and delayed inflammatory response and therefore, less severe heart lesions at earlier and later stages after PMCV infection. Secondly, farmed fish are kept in concentrations never seen in the wild (e.g. 50,000 fish in

3625-458: A small proportion of manganese dioxide. Oxygen levels in the atmosphere are trending slightly downward globally, possibly because of fossil-fuel burning. At standard temperature and pressure , oxygen is a colorless, odorless, and tasteless gas with the molecular formula O 2 , referred to as dioxygen. As dioxygen , two oxygen atoms are chemically bound to each other. The bond can be variously described based on level of theory, but

3770-596: A study in which cardiomyopathy syndrome (CMS), a severe cardiac disease in Atlantic salmon ( Salmo salar ), was investigated pertaining the effects of functional feeds with reduced lipid content and increased eicosapentaenoic acid levels in controlling CMS in salmon after infection with Piscine Myocarditis Virus (PMCV). Functional feeds are defined as high-quality feeds that beyond purposes of nutrition, they are formulated with health promoting features that could be beneficial in supporting disease resistance, such as CMS. Choosing

3915-400: A taboo against fish and other water-related animals, including waterfowl . Oxygen Oxygen is a chemical element with the symbol   O and atomic number 8. It is a member of the chalcogen group in the periodic table , a highly reactive nonmetal , and a potent oxidizing agent that readily forms oxides with most elements as well as with other compounds . Oxygen

4060-449: A triplet electronic ground state . An electron configuration with two unpaired electrons, as is found in dioxygen orbitals (see the filled π* orbitals in the diagram) that are of equal energy—i.e., degenerate —is a configuration termed a spin triplet state. Hence, the ground state of the O 2 molecule is referred to as triplet oxygen . The highest-energy, partially filled orbitals are antibonding , and so their filling weakens

4205-467: A weak condition or if the chemical concentration is too strong. A 2008 meta-analysis of available data shows that salmon farming reduces the survival of associated wild salmon populations. This relationship has been shown to hold for Atlantic, steelhead, pink, chum, and coho salmon. The decrease in survival or abundance often exceeds 50%. Fish as food Many species of fish are caught by humans and consumed as food in virtually all regions around

4350-580: Is the most abundant element in Earth's crust , and the third-most abundant element in the universe after hydrogen and helium . At standard temperature and pressure , two oxygen atoms will bind covalently to form dioxygen , a colorless and odorless diatomic gas with the chemical formula O 2 . Dioxygen gas currently constitutes 20.95% molar fraction of the Earth's atmosphere , though this has changed considerably over long periods of time in Earth's history . Oxygen makes up almost half of

4495-580: Is a corrosive byproduct of smog and thus an air pollutant . Oxygen was isolated by Michael Sendivogius before 1604, but it is commonly believed that the element was discovered independently by Carl Wilhelm Scheele , in Uppsala , in 1773 or earlier, and Joseph Priestley in Wiltshire , in 1774. Priority is often given for Priestley because his work was published first. Priestley, however, called oxygen "dephlogisticated air", and did not recognize it as

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4640-448: Is a food allergy to allergens which can be present in fish . This can result in an overreaction of the immune system and lead to severe physical symptoms from urticaria to angioedema and distributive shock . Allergic reactions can result from ingesting seafood, or by breathing in vapours from preparing or cooking seafood. The most severe allergic reaction is anaphylaxis , a medical emergency requiring immediate attention and

4785-504: Is a recommended consumption amount. Increasing intake of omega-3 fatty acids may slightly reduce the risk of a fatal heart attack, but likely has little effect on the overall number of deaths from cardiovascular disease. Fish bone is the most common food-related foreign body to cause airway obstruction . Choking on fish was responsible for about 4,500 reported accidents in the United Kingdom in 1998. A seafood allergy

4930-477: Is absorbed by specialized respiratory organs called gills , through the skin or via the gut ; in terrestrial animals such as tetrapods , oxygen in air is actively taken into the body via specialized organs known as lungs , where gas exchange takes place to diffuse oxygen into the blood and carbon dioxide out, and the body's circulatory system then transports the oxygen to other tissues where cellular respiration takes place. However in insects ,

5075-650: Is achieved by bubbling, cascade flow, or aqueous oxygen. Catfish in genus Clarias can breathe atmospheric air and can tolerate much higher levels of pollutants than trout or salmon, which makes aeration and water purification less necessary and makes Clarias species especially suited for intensive fish production. In some Clarias farms, about 10% of the water volume can consist of fish biomass . The risk of infections by parasites such as fish lice, fungi ( Saprolegnia spp.), intestinal worms (such as nematodes or trematodes ), bacteria (e.g., Yersinia spp., Pseudomonas spp.), and protozoa (such as dinoflagellates )

5220-490: Is also called "off-shore cultivation" when the cages are placed in the sea. They can be constructed of a wide variety of components. Fish are stocked in cages, artificially fed, and harvested when they reach market size. A few advantages of fish farming with cages are that many types of waters can be used (rivers, lakes, filled quarries, etc.), many types of fish can be raised, and fish farming can co-exist with sport fishing and other water uses. Cage farming of fishes in open seas

5365-653: Is also gaining in popularity. Given concerns of disease, poaching, poor water quality, etc., generally pond systems are considered simpler to start and easier to manage. Also, the past occurrences of cage-failures leading to escapes, have raised concern regarding the culture of non-native fish species in dam or open-water cages. On August 22, 2017, there was a massive failure of such cages at a commercial fishery in Washington state in Puget Sound , leading to release of nearly 300,000 Atlantic salmon in non-native waters. This

5510-513: Is associated with the atmospheric processes of aurora and airglow . The absorption in the Herzberg continuum and Schumann–Runge bands in the ultraviolet produces atomic oxygen that is important in the chemistry of the middle atmosphere. Excited-state singlet molecular oxygen is responsible for red chemiluminescence in solution. Table of thermal and physical properties of oxygen (O 2 ) at atmospheric pressure: Naturally occurring oxygen

5655-476: Is believed to risk endangering the native Pacific salmon species. Marine Scotland has kept records of caged fish escapes since 1999. They have recorded 357 fish escape incidents with 3,795,206 fish escaping into fresh and salt water. One company, Dawnfresh Farming Limited has been responsible for 40 incident and 152,790 Rainbow Trout escaping into freshwater lochs. Though the cage-industry has made numerous technological advances in cage construction in recent years,

5800-472: Is composed of three stable isotopes , O , O , and O , with O being the most abundant (99.762% natural abundance ). Most O is synthesized at the end of the helium fusion process in massive stars but some is made in the neon burning process . O is primarily made by the burning of hydrogen into helium during the CNO cycle , making it a common isotope in the hydrogen burning zones of stars. Most O

5945-418: Is economical only for high-value products, such as broodstock for egg production, fingerlings for net pen aquaculture operations, sturgeon production, research animals, and some special niche markets such as live fish. Raising ornamental coldwater fish ( goldfish or koi ), although theoretically much more profitable due to the higher income per weight of fish produced, has been successfully carried out only in

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6090-538: Is estimated to produce as much organic waste as equivalent to a town of people between 10,000 and 20,000 people each year. Today 50% of the world's seafood is farm-raised. These use irrigation ditches or farm ponds to raise fish. The basic requirement is to have a ditch or pond that retains water, possibly with an above-ground irrigation system (many irrigation systems use buried pipes with headers). Using this method, water allotments can be stored in ponds or ditches, usually lined with bentonite clay. In small systems,

6235-512: Is higher than in extensive farming, especially because of the high cost of fish feed . It must contain a much higher level of protein (up to 60%) than cattle feed and a balanced amino acid composition, as well. These higher protein-level requirements are a consequence of the higher feed efficiency of aquatic animals (higher feed conversion ratio [FCR], that is, kg of feed per kg of animal produced). Fish such as salmon have an FCR around 1.1 kg of feed per kg of salmon whereas chickens are in

6380-573: Is not clear whether this disinclination developed independently or whether it was introduced. It is certain, however, that no avoidance of fish occurs among southern Africa's earliest inhabitants, the Khoisan . Nevertheless, since the Bantu of southern Africa also share various cultural traits with the pastoralists further north in East Africa, it is believed that, at an unknown date, the taboo against

6525-418: Is often odourless and tasteless. Many fish eat algae and other organisms that contain biotoxins , which are defensive substances against predators. Biotoxins accumulated in fish/shellfish include brevetoxins , okadaic acid , saxitoxins , ciguatoxin and domoic acid . Except for ciguatoxine, high levels of these toxins are only found in shellfish. Both domoic acid and ciguatoxine can be deadly to humans;

6670-447: Is oxygen as a component of water, the major constituent of lifeforms. Oxygen in Earth's atmosphere is produced by biotic photosynthesis , in which photon energy in sunlight is captured by chlorophyll to split water molecules and then react with carbon dioxide to produce carbohydrates and oxygen is released as a byproduct . Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by

6815-984: Is particularly high in fish which may have lived in a river or estuary, such as salmon ( sa ke in Japanese cuisine ) or mackerel ( sa ba in Japanese cuisine). Such parasite infections can generally be avoided by boiling , grilling , preserving in salt or vinegar , or deep-freezing. In Japan, it is common to eat raw salmon and ikura ( roe ), but these foods are frozen overnight prior to eating to prevent infections from parasites, particularly Anisakis . The neologism " pescetarian " covers those who eat fish and other seafood , but not mammals and birds. A 1999 metastudy combined data from five studies from western countries. The metastudy reported mortality ratios , where lower numbers indicated fewer deaths, for pescetarians to be 0.82, vegetarians to be 0.84, and occasional meat eaters to be 0.84. Regular meat eaters and vegans shared

6960-538: Is permitted on some fast days when other meat is forbidden, but stricter fast days also prohibit fish with spines, while permitting invertebrate seafood such as shrimp and oysters , considering them "fish without blood". Some Buddhists and Hindus ( Brahmins of West Bengal , Odisha and Saraswat Brahmins of the Konkan ) abjure meat that is not fish. Muslim ( halal ) practice also treats fish differently from other animal foods, as it can be eaten without requiring

7105-598: Is prevented and oxygen levels stay high. Yields can be low if the fish grow ill from electrolyte stress. The composite fish culture system is a technology developed in India by the Indian Council of Agricultural Research in the 1970s. In this system, of both local and imported fish, a combination of five or six fish species is used in a single fish pond. These species are selected so that they do not compete for food among them by having different types of food habitats. As

7250-441: Is produced when N (made abundant from CNO burning) captures a He nucleus, making O common in the helium-rich zones of evolved, massive stars . Fifteen radioisotopes have been characterized, ranging from O to O. The most stable are O with a half-life of 122.24 seconds and O with a half-life of 70.606 seconds. All of the remaining radioactive isotopes have half-lives that are less than 27 seconds and

7395-408: Is reasonably and simply described as a covalent double bond that results from the filling of molecular orbitals formed from the atomic orbitals of the individual oxygen atoms, the filling of which results in a bond order of two. More specifically, the double bond is the result of sequential, low-to-high energy, or Aufbau , filling of orbitals, and the resulting cancellation of contributions from

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7540-401: Is similar to that in animal husbandry , especially at high population densities. However, animal husbandry is a larger and more technologically mature area of human agriculture and has developed better solutions to pathogen problems. Intensive aquaculture has to provide adequate water quality (oxygen, ammonia, nitrite, etc.) levels to minimize stress on the fish. This requirement makes control of

7685-622: Is sometimes referred to as the "Cushitic fish-taboo", as Cushitic speakers are believed to have been responsible for the introduction of fish avoidance to East Africa , though not all Cushitic groups avoid fish. The zone of the fish taboo roughly coincides with the area where Cushitic languages are spoken, and as a general rule, speakers of Nilo-Saharan and Semitic languages do not have this taboo, and indeed many are watermen. The few Bantu and Nilotic groups in East Africa that do practice fish avoidance also reside in areas where Cushites appear to have lived in earlier times. Within East Africa,

7830-712: Is temperature-dependent, and about twice as much ( 14.6  mg/L ) dissolves at 0 °C than at 20 °C ( 7.6  mg/L ). At 25 °C and 1 standard atmosphere (101.3  kPa ) of air, freshwater can dissolve about 6.04  milliliters  (mL) of oxygen per liter , and seawater contains about 4.95 mL per liter. At 5 °C the solubility increases to 9.0 mL (50% more than at 25 °C) per liter for freshwater and 7.2 mL (45% more) per liter for sea water. Oxygen condenses at 90.20  K (−182.95 °C, −297.31 °F) and freezes at 54.36 K (−218.79 °C, −361.82 °F). Both liquid and solid O 2 are clear substances with

7975-423: Is that many of these fish breed only during monsoon. Even if fish are collected from the wild, they can be mixed with other species, as well. Thus, a major problem in fish farming is the lack of availability of good-quality stock. To overcome this problem, ways have now been worked out to breed these fish in ponds using hormonal stimulation. This has ensured the supply of pure fish stock in desired quantities. One of

8120-421: Is the other form of fish farming. Extensive aquaculture is more basic than intensive aquaculture in that less effort is put into the husbandry of the fish. Extensive aquaculture is done in the ocean, natural and man-made lakes, bays, rivers, and Fiords. Fish are contained within these habitats by multiple mesh enclosures which also function as trapping nets during harvest (Figure 3) (4). Since fish are susceptible to

8265-435: Is the result of the oxygen cycle . This biogeochemical cycle describes the movement of oxygen within and between its three main reservoirs on Earth: the atmosphere, the biosphere, and the lithosphere . The main driving factor of the oxygen cycle is photosynthesis , which is responsible for modern Earth's atmosphere. Photosynthesis releases oxygen into the atmosphere, while respiration , decay , and combustion remove it from

8410-420: Is treated urgently with epinephrine . Some species of fish, notably the fugu pufferfish used for sushi , can result in serious food poisoning if not prepared properly. These fish always contain toxins as a natural defense against predators ; it is not present due to environmental circumstances. Particularly, fugu has a lethal dose of tetrodotoxin in its internal organs and must be prepared by

8555-463: Is unusual among the planets of the Solar System in having such a high concentration of oxygen gas in its atmosphere: Mars (with 0.1% O 2 by volume) and Venus have much less. The O 2 surrounding those planets is produced solely by the action of ultraviolet radiation on oxygen-containing molecules such as carbon dioxide. The unusually high concentration of oxygen gas on Earth

8700-522: Is usually given priority in the discovery. The French chemist Antoine Laurent Lavoisier later claimed to have discovered the new substance independently. Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele had also dispatched a letter to Lavoisier on September 30, 1774, which described his discovery of the previously unknown substance, but Lavoisier never acknowledged receiving it (a copy of

8845-618: The Earth , the Moon , Mars , and meteorites , but were long unable to obtain reference values for the isotope ratios in the Sun , believed to be the same as those of the primordial solar nebula . Analysis of a silicon wafer exposed to the solar wind in space and returned by the crashed Genesis spacecraft has shown that the Sun has a higher proportion of oxygen-16 than does the Earth. The measurement implies that an unknown process depleted oxygen-16 from

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8990-463: The Earth's crust in the form of various oxides such as water , carbon dioxide , iron oxides and silicates . All eukaryotic organisms , including plants , animals , fungi , algae and most protists , need oxygen for cellular respiration , which extracts chemical energy by the reaction of oxygen with organic molecules derived from food and releases carbon dioxide as a waste product. In aquatic animals , dissolved oxygen in water

9135-565: The Greek roots ὀξύς (oxys) ( acid , literally 'sharp', from the taste of acids) and -γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids. Chemists (such as Sir Humphry Davy in 1812) eventually determined that Lavoisier was wrong in this regard, but by then the name was too well established. Oxygen entered the English language despite opposition by English scientists and

9280-580: The New Testament Luke 24 – Jesus's eating of a fish and Jesus telling his disciples where to catch fish, before cooking it for them to eat. Seasonal religious prohibitions against eating meat do not usually include fish. For example, non-fish meat was forbidden during Lent and on all Fridays of the year in pre- Vatican II Roman Catholicism , but fish was permitted (as were eggs). (See Fasting in Catholicism .) In Eastern Orthodoxy , fish

9425-491: The Pacific coast of Canada , the louse-induced mortality of pink salmon in some regions is commonly over 80%. In Scotland, official figures show that more than nine million fish were lost to disease, parasites, botched treatment attempts and other problems on fish farms between 2016 and 2019. One of the treatments for parasite infestations involved bathing fish in hydrogen peroxide, which can harm or kill farmed fish if they are in

9570-543: The Sargasso Sea breeding grounds, for their farms. The European eel is threatened with extinction because of the excessive catch of glass eels by Spanish fishermen and overfishing of adult eels in, e.g., the Dutch IJsselmeer . Although European eel larvae can survive for several weeks, the full life cycle has not yet been achieved in captivity. There is a growing consensus that fish can feel pain . Despite

9715-516: The US Food and Drug Administration (FDA), the risk from mercury by eating fish and shellfish is not a health concern for most people. However, certain seafood contains sufficient mercury to harm an unborn baby or young child's developing nervous system. The FDA makes three recommendations for child-bearing women and young children: These recommendations are also advised when feeding fish and shellfish to young children, but in smaller portions. When

9860-625: The aquarium trade. The vast majority of freshwater fish in the aquarium trade originate from farms in Eastern and Southern Asia, eastern Europe, Florida and South America that use either indoor tank systems or outdoor pond systems, while farming of fish for the marine aquarium trade happens at a much smaller scale. In 2022 24% of fishers and fish farmers and 62% of workers in post-harvest sector were women. Aquaculture makes use of local photosynthetic production (extensive) or fish that are fed with external food supply (intensive). Extensive aquaculture

10005-470: The shells and skeletons of marine organisms to determine the climate millions of years ago (see oxygen isotope ratio cycle ). Seawater molecules that contain the lighter isotope , oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18, and this disparity increases at lower temperatures. During periods of lower global temperatures, snow and rain from that evaporated water tends to be higher in oxygen-16, and

10150-427: The sustainable yields of wild fish populations. While fish farming is practised worldwide, China alone provides 62% of the world's farmed fish production. As of 2016, more than 50% of seafood was produced by aquaculture. In the last three decades, aquaculture has been the main driver of the increase in fisheries and aquaculture production, with an average growth of 5.3 percent per year in the period 2000–2018, reaching

10295-430: The thermal decomposition of potassium nitrate . In Bugaj's view, the isolation of oxygen and the proper association of the substance to that part of air which is required for life, provides sufficient evidence for the discovery of oxygen by Sendivogius. This discovery of Sendivogius was however frequently denied by the generations of scientists and chemists which succeeded him. It is also commonly claimed that oxygen

10440-557: The 17th and the 18th century but none of them recognized it as a chemical element . This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory , which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher , and modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston,

10585-407: The 2.5 kg of feed per kg of chicken range. Fish do not use energy to keep warm, eliminating some carbohydrates and fats in the diet, required to provide this energy. This may be offset, though, by the lower land costs and the higher production which can be obtained due to the high level of input control. Aeration of the water is essential, as fish need a sufficient oxygen level for growth. This

10730-579: The 21st century. The increased incidences of dangerous viral diseases of koi carp, together with the high value of the fish, has led to initiatives in closed-system koi breeding and growing in a number of countries. Today, a few commercially successful intensive koi-growing facilities are operating in the UK, Germany, and Israel. Some producers have adapted their intensive systems in an effort to provide consumers with fish that do not carry dormant forms of viruses and diseases. In 2016, juvenile Nile tilapia were given

10875-531: The 2s electrons, after sequential filling of the low σ and σ orbitals; σ overlap of the two atomic 2p orbitals that lie along the O–O molecular axis and π overlap of two pairs of atomic 2p orbitals perpendicular to the O–O molecular axis, and then cancellation of contributions from the remaining two 2p electrons after their partial filling of the π orbitals. This combination of cancellations and σ and π overlaps results in dioxygen's double-bond character and reactivity, and

11020-536: The American scientist Robert H. Goddard became the first person to develop a rocket engine that burned liquid fuel; the engine used gasoline for fuel and liquid oxygen as the oxidizer . Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926, in Auburn, Massachusetts , US. In academic laboratories, oxygen can be prepared by heating together potassium chlorate mixed with

11165-836: The Google headquarters in Mountain View, California, showing off feed made from seaweed extracts, yeast , and algae grown in bioreactors ." Not only do the feeds for carnivorous fish, like certain salmon species, remain controversial due to the containment of wild caught fish like anchovies, but they are not helping the health of the fish, as is the case in Norway. Between 2003 and 2007, Aldrin et al. examined three infectious diseases in Norwegian salmon fish farms—heart and skeletal muscle inflammation, pancreas disease, and infectious salmon anemia. In 2014, Martinez-Rubio et al. conducted

11310-484: The Philosopher's Stone drawn from the source of nature and manual experience"] (1604) described a substance contained in air, referring to it as 'cibus vitae' (food of life, ) and according to Polish historian Roman Bugaj, this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by

11455-438: The Sun's disk of protoplanetary material prior to the coalescence of dust grains that formed the Earth. Oxygen presents two spectrophotometric absorption bands peaking at the wavelengths 687 and 760  nm . Some remote sensing scientists have proposed using the measurement of the radiance coming from vegetation canopies in those bands to characterize plant health status from a satellite platform. This approach exploits

11600-1020: The antimicrobial/algaecidal properties of copper alloys prevent biofouling , which can briefly be described as the undesirable accumulation, adhesion, and growth of microorganisms, plants, algae , tube worms , barnacles , mollusks , and other organisms. The resistance of organism growth on copper alloy nets also provides a cleaner and healthier environment for farmed fish to grow and thrive. Traditional netting involves regular and labor-intensive cleaning. In addition to its antifouling benefits, copper netting has strong structural and corrosion-resistant properties in marine environments. Copper-zinc brass alloys are deployed in commercial-scale aquaculture operations in Asia, South America, and USA (Hawaii). Extensive research, including demonstrations and trials, are being implemented on two other copper alloys: copper-nickel and copper-silicon. Each of these alloy types has an inherent ability to reduce biofouling, cage waste, disease, and

11745-493: The atmosphere. In the present equilibrium, production and consumption occur at the same rate. Free oxygen also occurs in solution in the world's water bodies. The increased solubility of O 2 at lower temperatures (see Physical properties ) has important implications for ocean life, as polar oceans support a much higher density of life due to their higher oxygen content. Water polluted with plant nutrients such as nitrates or phosphates may stimulate growth of algae by

11890-575: The average annual increase in global apparent food fish consumption (3.2 percent) has outpaced population growth (1.6 percent) and exceeded consumption of meat from all terrestrial animals , combined (2.8 percent) and individually (bovine, ovine, porcine, etc.), except poultry (4.9 percent). In per capita terms, food fish consumption has grown from 9.0 kg (19.8 lb) in 1961 to 20.2 kg (45 lb) in 2015, at an average rate of about 1.5 percent per year. The expansion in consumption has been driven not only by increased production, but also by

12035-471: The best method of cooking a turbot ." Globally, fish and fish products provide an average of only about 34 calories per capita per day. However, more than as an energy source, the dietary contribution of fish is significant in terms of high-quality, easily digested animal proteins and especially in fighting micronutrient deficiencies. A portion of 150g of fish provides about 50 to 60 percent of an adult's daily protein requirement. Fish proteins are essential in

12180-412: The bond order from three to two. Because of its unpaired electrons, triplet oxygen reacts only slowly with most organic molecules, which have paired electron spins; this prevents spontaneous combustion. In the triplet form, O 2 molecules are paramagnetic . That is, they impart magnetic character to oxygen when it is in the presence of a magnetic field, because of the spin magnetic moments of

12325-812: The competition between organisms for limited resources. Also, when foreign fish interbreed with wild species, they upset the genetic variability of the species, making them more prone to disease and infection. The high density of fish in these mesh tanks is very tempting for predators of the sea and air (19). To protect the harvest from predators protective netting is set up at a high cost. Often times predatorial fish and mammals like seals, sharks, and tuna get caught in these barrier nets and die. Some farmers protect their stocks from predatorial birds such as pelicans and albatross by shooting these sometimes endangered creatures. In these kinds of systems fish production per unit of surface can be increased at will, as long as sufficient oxygen , fresh water and food are provided. Because of

12470-454: The consumption of fish was similarly introduced from East Africa by cattle-herding peoples who somehow managed to get their livestock past the aforementioned tsetse fly endemic regions. Certain species of fish are also forbidden in Judaism such as the freshwater eel ( Anguillidae ) and all species of catfish . Although they live in water, they appear to have no fins or scales (except under

12615-444: The diatomic elemental molecules in those gases. The first commercial method of producing oxygen was chemical, the so-called Brin process involving a reversible reaction of barium oxide . It was invented in 1852 and commercialized in 1884, but was displaced by newer methods in early 20th century. By the late 19th century scientists realized that air could be liquefied and its components isolated by compressing and cooling it. Using

12760-546: The diet of some densely populated countries where the total protein intake is low, and are particularly important in diets in small island developing States (SIDS). Intermediate Technology Publications wrote in 1992 that "Fish provides a good source of high quality protein and contains many vitamins and minerals. It may be classed as either whitefish, oily fish, or shellfish. Whitefish, such as haddock and seer, contain very little fat (usually less than 1%) whereas oily fish, such as sardines, contain between 10–25%. The latter, as

12905-505: The diets of carnivores. Research is underway to try to change this, such that even salmon and other carnivores could be successfully fed with vegetable products. The F3 Challenge (Fish-Free Feed Challenge), as explained by a report from Wired in February 2017, "is a race to sell 100,000 metric tons of fish food, without the fish. Earlier this month, start-ups from places like Pakistan, China, and Belgium joined their American competition at

13050-502: The eating of cetacean meat, such as whale, dolphin or porpoise, because they are not "fish with fins and scales"; nor, as mammals, do they chew their cud and have cloven hooves, as required by Leviticus 11:9–12 . Jewish ( kosher ) practice treats fish differently from other animal foods. The distinction between fish and "meat" is codified by the Jewish dietary law of kashrut , regarding the mixing of milk and meat, which does not forbid

13195-466: The electron spins are paired. It is much more reactive with common organic molecules than is normal (triplet) molecular oxygen. In nature, singlet oxygen is commonly formed from water during photosynthesis, using the energy of sunlight. It is also produced in the troposphere by the photolysis of ozone by light of short wavelength and by the immune system as a source of active oxygen. Carotenoids in photosynthetic organisms (and possibly animals) play

13340-437: The elements, site placement is essential to ensure the rapid growth of the targeted species. The drawback of these facilities is that they depend on the surrounding area for good water quality in order to reduce mortality and increase the survivorship and growth rate of the fish (19). Fish chosen for extensive aquaculture are very hardy and often do well in high densities. Seaweed, prawns, mussels, carp, tilapia, tuna and salmon are

13485-509: The environment. The flow allows chemicals, parasites, waste and diseases to spread in the enclosed environment, and this is not beneficial for the natural environment. Another negative consequence is the high escape rate of the cultured fish from these open net pens. These escaped fish also pose a high risk to the surrounding ecosystems. The amount of organic waste produced by fish farms is also alarming. A salmon farm in Scotland , for instance,

13630-572: The fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book The Botanic Garden (1791) by Erasmus Darwin , grandfather of Charles Darwin . John Dalton 's original atomic hypothesis presumed that all elements were monatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula

13775-399: The first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium . In his work Pneumatica , Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in

13920-433: The fish are often fed commercial fish food, and their waste products can help fertilize the fields. In larger ponds, the pond grows water plants and algae as fish food. Some of the most successful ponds grow introduced strains of plants, as well as introduced strains of fish. Control of water quality is crucial. Fertilizing, clarifying, and pH control of the water can increase yields substantially, as long as eutrophication

14065-440: The fish in large cages floating in the water. The fish are living in natural water but are isolated with a net. Because the only barrier separating the fish from the surrounding environment is a net, this allows the water to flow from the ‘natural’ surrounding through the fish farms. The site of the fish farm is crucial for the farm to be a success or not. Before any fish farm is settled, it is highly recommended to be selective with

14210-558: The fish taboo is found no further than Tanzania. This is attributed to the local presence of the tsetse fly and in areas beyond, which likely acted as a barrier to further southern migrations by wandering pastoralists , the principal fish-avoiders. Zambia and Mozambique 's Bantus were therefore spared subjugation by pastoral groups, and they consequently nearly all consume fish. There is also another center of fish avoidance in Southern Africa , among mainly Bantu speakers . It

14355-546: The fry are raised in long, shallow, concrete tanks, fed with fresh stream water. The fry receive commercial fish food in pellets. While not as efficient as the New Alchemists' method, it is also far simpler and has been used for many years to stock streams with sport fish. European eel ( Anguilla anguilla ) aquaculturalists procure a limited supply of glass eels, juvenile stages of the European eel which swim north from

14500-486: The global total of 149 million tonnes in 2015, Asia consumed more than two-thirds (106 million tonnes at 24.0 kg per capita). Oceania and Africa consumed the lowest share. The shift is the result of structural changes in the sector and in particular the growing role of Asian countries in fish production, as well as a significant gap between the economic growth rates of the world's more mature fish markets and those of many increasingly important emerging markets around

14645-467: The high amount of organic waste produced by the fish which settles below their pens(4). Phytoplankton and algae break down fecal matter and residual fish meal reducing the amount of available oxygen in the water column, which chokes and kills the Benthic organisms. Another serious problem acquainted with extensive aquaculture is the introduction of invasive species into ecosystems (10). Escaped fish increase

14790-593: The highest mortality ratio of 1.00. However, the "lower mortality was due largely to the relatively low prevalence of smoking in these [vegetarian] cohorts". Since fish is animal flesh, the Vegetarian Society has stated that vegetarian diets cannot contain fish. Religious rites and rituals regarding food also tend to classify the birds of the air and the fish of the sea separately from land-bound mammals. Sea-bound mammals are often treated as fish under religious laws – as in Jewish dietary law, which forbids

14935-399: The idea; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process. Polish alchemist , philosopher , and physician Michael Sendivogius (Michał Sędziwój) in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti ["Twelve Treatises on

15080-482: The largest problems with freshwater pisciculture is that it can use a million gallons of water per acre (about 1 m of water per m) each year. Extended water purification systems allow for the reuse ( recycling ) of local water. The largest-scale pure fish farms use a system derived (admittedly much refined) from the New Alchemy Institute in the 1970s. Basically, large plastic fish tanks are placed in

15225-504: The letter was found in Scheele's belongings after his death). Lavoisier conducted the first adequate quantitative experiments on oxidation and gave the first correct explanation of how combustion works. He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a chemical element . In one experiment, Lavoisier observed that there

15370-428: The majority of these have half-lives that are less than 83 milliseconds. The most common decay mode of the isotopes lighter than O is β decay to yield nitrogen, and the most common mode for the isotopes heavier than O is beta decay to yield fluorine . Oxygen is the most abundant chemical element by mass in the Earth's biosphere , air, sea and land. Oxygen is the third most abundant chemical element in

15515-402: The mixing of milk and fish. Modern Jewish legal practice ( halakha ) on kashrut classifies the flesh of both mammals and birds as "meat"; fish are considered to be parve , neither meat nor a dairy food. (The preceding portion refers only to the halakha of Ashkenazi Jews ; Sephardic Jews do not mix fish with dairy.) Ichthys has become a symbol of Christianity since ancient times. In

15660-533: The most prominent forms of extensive aqua cultured seafood. Extensive aquaculture facilities have negative impacts on the environment as well. Natural habitats are destroyed in the development of man made ponds used for extensive aquaculture. In the Philippines, shrimp aquaculture is responsible for the destruction of thousands of acres of mangrove fields which serve as nurseries and living habitats for many marine organisms. Benthic habitats are being depleted due to

15805-418: The most successful and biodiverse terrestrial clade , oxygen is directly conducted to the internal tissues via a deep network of airways . Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins , nucleic acids , carbohydrates and fats , as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms

15950-437: The need for antibiotics, while simultaneously maintaining water circulation and oxygen requirements. Other types of copper alloys are also being considered for research and development in aquaculture operations. In Southeast Asia , the traditional cage farming platform is called kelong . The open net pens system is a method that takes place in natural waters, such as rivers, lakes, near the coast or offshore. The breeders rear

16095-494: The nitroaereus must have combined with it. He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke , Ole Borch , Mikhail Lomonosov , and Pierre Bayen all produced oxygen in experiments in

16240-482: The ocean conservation organization Oceana examined over 1,200 seafood samples of seafood sold in the U.S. between 2010 and 2012, they found one-third were mislabelled. The highest rate of mislabelling occurred with snapper at 87 percent, followed by tuna at 57 percent. If fish and shellfish inhabit polluted waters , they can accumulate other toxic chemicals, particularly fat-soluble pollutants containing chlorine or bromine, dioxins or PCBs . Parasites in fish are

16385-781: The others will only cause diarrhea , dizziness and a (temporary) feeling of claustrophobia . Shellfish are filter feeders and, therefore, accumulate toxins produced by microscopic algae , such as dinoflagellates and diatoms , and cyanobacteria . There are four syndromes called shellfish poisoning which can result in humans, sea mammals and seabirds from the ingestion of toxic shellfish. These are primarily associated with bivalve molluscs , such as mussels , clams , oysters and scallops . Fish like anchovies can also concentrate toxins such as domoic acid. If suspected, medical attention should be sought. The toxins responsible for most shellfish and fish poisonings, including ciguatera and scombroid poisoning, are heat-resistant to

16530-481: The pathogen problem more difficult. Intensive aquaculture requires tight monitoring and a high level of expertise of the fish farmer. Very-high-intensity recycle aquaculture systems (RAS, also Recirculating Aquaculture Systems), where all the production parameters are controlled, are being used for high-value species. By recycling water, little is used per unit of production. However, the process has high capital and operating costs. The higher cost structures mean that RAS

16675-454: The photosynthetic activities of autotrophs such as cyanobacteria , chloroplast -bearing algae and plants. A much rarer triatomic allotrope of oxygen , ozone ( O 3 ), strongly absorbs the UVB and UVC wavelengths and forms a protective ozone layer at the lower stratosphere , which shields the biosphere from ionizing ultraviolet radiation . However, ozone present at the surface

16820-506: The plants are fertilized by the nitrates and phosphates .Other wastes are strained out by the hydroponic media, which double as an aerated pebble-bed filter. This system, properly tuned, produces more edible protein per unit area than any other. A wide variety of plants can grow well in the hydroponic beds. Most growers concentrate on herbs (e.g. parsley and basil ), which command premium prices in small quantities all year long. The most common customers are restaurant wholesalers. Since

16965-476: The point where conventional cooking methods do not eliminate them. Fish products, especially those from apex and higher-order consumers up the food chain , have been shown to contain varying amounts of heavy or toxic metals due to biomagnification . Toxicity is a function of solubility, and insoluble compounds often exhibit negligible toxicity. Organometallic forms such as dimethyl mercury and tetraethyl lead can be extremely toxic. According to

17110-522: The possibility of parasites (see Sashimi article). Parasitic infections from freshwater fish are a serious problem in some parts of the world, particularly Southeast Asia . Fish that spend part of their life cycle in brackish or fresh water, like salmon (an anadromous coastalfish closely related to trout ), are a particular problem. A study in Seattle, Washington showed that 100% of wild salmon had roundworm larvae capable of infecting people. In

17255-576: The preservation techniques used in different cultures have since become unnecessary but are still performed for their resulting taste and texture when consumed. The British historian William Radcliffe wrote in Fishing from the Earliest Times : "The Emperor Domitian ( Juvenal , IV. ) ordered a special sitting of the Senate to deliberate and advise on a matter of such grave State importance as

17400-458: The remainder of this article. Trioxygen ( O 3 ) is usually known as ozone and is a very reactive allotrope of oxygen that is damaging to lung tissue. Ozone is produced in the upper atmosphere when O 2 combines with atomic oxygen made by the splitting of O 2 by ultraviolet (UV) radiation. Since ozone absorbs strongly in the UV region of the spectrum , the ozone layer of

17545-451: The requirement of sufficient fresh water, a massive water purification system must be integrated in the fish farm. One way to achieve this is to combine hydroponic horticulture and water treatment , see below. The exception to this rule are cages which are placed in a river or sea, which supplements the fish crop with sufficient oxygenated water. Some environmentalists object to this practice. The cost of inputs per unit of fish weight

17690-439: The risk of damage and escape due to storms is always a concern. Semi-submersible marine technology is beginning to impact fish farming. In 2018, 1.5 million salmon are in the middle of a year-long trial at Ocean Farm 1 off the coast of Norway . The semi-submersible US$ 300 million project is the world's first deep-sea aquaculture project, and includes 61-meter (200 ft)-high by 91-meter (300 ft)-diameter pen made from

17835-519: The ritualistic slaughter that is prescribed for other halal animals. Among the Somali people , most clans have a taboo against the consumption of fish, and do not intermarry with the few occupational clans that do eat it. There are taboos on eating fish among many upland pastoralists and agriculturalists (and even some coastal peoples) inhabiting parts of southeastern Egypt , Ethiopia , Eritrea , Somalia , Kenya , and northern Tanzania . This

17980-407: The same study farm -raised salmon did not have any roundworm larvae. Parasite infection from raw fish is rare in the developed world (fewer than 40 cases per year in the United States ), and involves mainly three kinds of parasites: Clonorchis sinensis (a trematode / fluke ), Anisakis (a nematode /roundworm) and Diphyllobothrium (a cestode / tapeworm ). Infection risk of Anisakis

18125-414: The seawater left behind tends to be higher in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climate. Paleoclimatologists also directly measure this ratio in the water molecules of ice core samples as old as hundreds of thousands of years. Planetary geologists have measured the relative quantities of oxygen isotopes in samples from

18270-413: The site location of the farm. The site must be examined on some essential elements. Important conditions on the location are: Despite these important site conditions, the open net pen method was very popular in Norway and China. This is because of the cost friendliness and efficiency of this method. Because of the ocean's water flow and other reasons, open net pen culture is seen as a high-risk method for

18415-542: The skin of wild salmon during free-swimming, planktonic nauplii and copepodid larval stages, which can persist for several days. Large numbers of highly populated, open-net salmon farms can create exceptionally large concentrations of sea lice; when exposed in river estuaries containing large numbers of open-net farms, many young wild salmon are infected, and do not survive as a result. Adult salmon may survive otherwise critical numbers of sea lice, but small, thin-skinned juvenile salmon migrating to sea are highly vulnerable. On

18560-507: The system lives in a greenhouse , it adapts to almost all temperate climates, and may also adapt to tropical climates . The main environmental impact is discharge of water that must be salted to maintain the fishes' electrolyte balance. Current growers use a variety of proprietary tricks to keep fish healthy, reducing their expenses for salt and wastewater discharge permits. Some veterinary authorities speculate that ultraviolet ozone disinfectant systems (widely used for ornamental fish) may play

18705-486: The universe, after hydrogen and helium. About 0.9% of the Sun 's mass is oxygen. Oxygen constitutes 49.2% of the Earth's crust by mass as part of oxide compounds such as silicon dioxide and is the most abundant element by mass in the Earth's crust . It is also the major component of the world's oceans (88.8% by mass). Oxygen gas is the second most common component of the Earth's atmosphere , taking up 20.8% of its volume and 23.1% of its mass (some 10 tonnes). Earth

18850-401: The unpaired electrons in the molecule, and the negative exchange energy between neighboring O 2 molecules. Liquid oxygen is so magnetic that, in laboratory demonstrations, a bridge of liquid oxygen may be supported against its own weight between the poles of a powerful magnet. Singlet oxygen is a name given to several higher-energy species of molecular O 2 in which all

18995-435: The upper atmosphere functions as a protective radiation shield for the planet. Near the Earth's surface, it is a pollutant formed as a by-product of automobile exhaust . At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft . The metastable molecule tetraoxygen ( O 4 ) was discovered in 2001, and was assumed to exist in one of the six phases of solid oxygen . It

19140-709: The vast number of fish consumed, fish welfare has historically received little attention. Farmed fish are usually raised in overcrowded environments, making them susceptible to stress, injuries, aggression and diseases. These conditions prevent them from engaging in natural behaviors such as nesting or migration. Overcrowding often leads to poor water quality due to fish waste and antibiotics use. Sea lice infestations are common and can cause painful lesion, but are typically treated with harsh chemicals. Additionally, fish are genetically engineered to grow larger and faster, leading to health problems such as cataracts and abnormal heart shapes. The issue of feeds in fish farming has been

19285-451: The vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration . In the late 17th century, Robert Boyle proved that air is necessary for combustion. English chemist John Mayow (1641–1679) refined this work by showing that fire requires only

19430-626: The world, particularly in Asia. Over 32,000 species of fish have been described, making them the most diverse group of vertebrates. In addition, there are many species of shellfish . However, only a small number of species are commonly eaten by humans. Fish can be prepared in a variety of ways. It can be served uncooked ( raw food , e.g., sashimi ); cured by marinating ( e.g., ceviche ), pickling ( e.g., pickled herring ) or smoking ( e.g., smoked salmon ); or cooked by baking , frying ( e.g., fish and chips ), grilling , poaching ( e.g., court-bouillon ) or steaming . Many of

19575-534: The world. Fish has been an important dietary source of protein and other nutrients . The English language does not have a special culinary name for food prepared from fish like with other animals (as with pig vs. pork ), or as in other languages (such as Spanish pez vs. pescado ). In culinary and fishery contexts, fish may include so-called shellfish such as molluscs , crustaceans , and echinoderms ; more expansively, seafood covers both fish and other marine life used as food. Since 1961,

19720-428: Was HO, leading to the conclusion that the atomic mass of oxygen was 8 times that of hydrogen, instead of the modern value of about 16. In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811 Amedeo Avogadro had arrived at the correct interpretation of water's composition, based on what is now called Avogadro's law and

19865-408: Was first discovered by Swedish pharmacist Carl Wilhelm Scheele . He had produced oxygen gas by heating mercuric oxide (HgO) and various nitrates in 1771–72. Scheele called the gas "fire air" because it was then the only known agent to support combustion. He wrote an account of this discovery in a manuscript titled Treatise on Air and Fire , which he sent to his publisher in 1775. That document

20010-451: Was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx . Highly combustible materials that leave little residue , such as wood or coal, were thought to be made mostly of phlogiston; non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test

20155-491: Was independently developed in 1895 by German engineer Carl von Linde and British engineer William Hampson . Both men lowered the temperature of air until it liquefied and then distilled the component gases by boiling them off one at a time and capturing them separately. Later, in 1901, oxyacetylene welding was demonstrated for the first time by burning a mixture of acetylene and compressed O 2 . This method of welding and cutting metal later became common. In 1923,

20300-445: Was no overall increase in weight when tin and air were heated in a closed container. He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book Sur la combustion en général , which

20445-465: Was not sensibly different from that of common air , but I fancied that my breast felt peculiarly light and easy for some time afterwards." Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air", which was included in the second volume of his book titled Experiments and Observations on Different Kinds of Air . Because he published his findings first, Priestley

20590-408: Was proven in 2006 that this phase, created by pressurizing O 2 to 20  GPa , is in fact a rhombohedral O 8 cluster . This cluster has the potential to be a much more powerful oxidizer than either O 2 or O 3 and may therefore be used in rocket fuel . A metallic phase was discovered in 1990 when solid oxygen is subjected to a pressure of above 96 GPa and it

20735-504: Was published in 1777. In the meantime, on August 1, 1774, an experiment conducted by the British clergyman Joseph Priestley focused sunlight on mercuric oxide contained in a glass tube, which liberated a gas he named "dephlogisticated air". He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, Priestley wrote: "The feeling of it to my lungs

20880-462: Was published in 1777. In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and azote (Gk. ἄζωτον "lifeless"), which did not support either. Azote later became nitrogen in English, although it has kept the earlier name in French and several other European languages. Lavoisier renamed 'vital air' to oxygène in 1777 from

21025-420: Was shown in 1998 that at very low temperatures, this phase becomes superconducting . Oxygen dissolves more readily in water than nitrogen, and in freshwater more readily than in seawater. Water in equilibrium with air contains approximately 1 molecule of dissolved O 2 for every 2 molecules of N 2 (1:2), compared with an atmospheric ratio of approximately 1:4. The solubility of oxygen in water

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