Aquarium

   
A tropical display tank at the Georgia Aquarium

An aquarium (plural aquariums or aquaria) is a vivarium, usually contained in a clear-sided container (typically constructed of glass or high-strength plastic) in which water-dwelling plants and animals (usually fish, and sometimes invertebrates, as well as amphibians, marine mammals, and reptiles) are kept in captivity, often for public display; or it is an establishment featuring such displays. Aquarium keeping is a popular hobby around the world, with about 60 million enthusiasts worldwide. From the 1850s, when the predecessor of the modern aquarium was first developed as a novel curiosity, the ranks of aquarists have swelled as more sophisticated systems including lighting and filtration systems were developed to keep aquarium fish healthy. Public aquaria reproduce the home aquarist's hobby on a grand scale — the Osaka Aquarium, for example, boasts a tank of 5,400 m³ (1.4 million U.S. gallons) and a collection of about 580 species of aquatic life.

A wide variety of aquaria are now kept by hobbyists, ranging from a simple bowl housing a single fish to complex simulated ecosystems with carefully engineered support systems. Aquaria are usually classified as containing fresh or salt water, at tropical or cold water temperatures. These characteristics, and others, determine the type of fish and other inhabitants that can survive and thrive in the aquarium. Inhabitants for aquaria are often collected from the wild, although there is a growing list of organisms that are bred in captivity for supply to the aquarium trade.

The careful aquarist dedicates considerable effort to maintaining a tank ecology that mimics its inhabitants' natural habitat. Controlling water quality includes managing the inflow and outflow of nutrients, most notably the management of waste produced by tank inhabitants. The nitrogen cycle describes the flow of nitrogen from input via food, through toxic nitrogenous waste produced by tank inhabitants, to metabolism to less toxic compounds by beneficial bacteria populations. Other components in maintaining a suitable aquarium environment include appropriate species selection, management of biological loading, and good physical design.

South East Asian fish in the aquarium at Bristol Zoo, Bristol, England. The tank is about 2 metres (6 feet) high.

History and development

Etymology

The word aquarium itself is taken directly from the latin aqua, meaning water, with the suffix -rium, meaning "place" or "building".

Ancient practices

Koi have been kept in decorative ponds for centuries in China and Japan.

The keeping of fish in confined or artificial environments is a practice with deep roots in history. Ancient Sumerians were known to keep wild-caught fish in ponds, before preparing them for meals. In China, selective breeding of carp into today's popular koi and goldfish is believed to have begun over 2,000 years ago. Depictions of the sacred fish of Oxyrhynchus kept in captivity in rectangular temple pools have been found in ancient Egyptian art. Many other cultures also have a history of keeping fish for both functional and decorative purposes. The Chinese brought goldfish indoors during the Song dynasty to enjoy them in large ceramic vessels.

Glass enclosures

The concept of an aquarium, designed for the observation of fish in an enclosed, transparent tank to be kept indoors, emerged more recently. However, it is difficult to pinpoint the exact date of this development. In 1665 the diarist Samuel Pepys recorded seeing in London "a fine rarity, of fishes kept in a glass of water, that will live so forever, and finely marked they are, being foreign." The fish observed by Pepys were likely to have been the paradise fish, Macropodus opercularis, a familiar garden fish in Canton, China, where the East India Company was then trading. In the 18th century, the biologist Abraham Trembley kept hydra found in the garden canals of the Bentinck residence 'Sorgvliet' in the Netherlands, in large cylindrical glass vessels for study. The concept of keeping aquatic life in glass containers, then, dates to at latest this period.

Popularization

The keeping of fish in an aquarium first became a popular hobby in Britain only after ornate aquaria in cast-iron frames were featured at the Great Exhibition of 1851. The framed-glass aquarium was a specialized version of the glazed Wardian case developed for British horticulturists in the 1830s to protect exotic plants on long sea voyages. (One feature of some 19th-century aquaria that would prove curious to hobbyists today was the use of a metal base panel so that the aquarium water could be heated by flame.) Germans rivaled the British in their interest, and by the turn of the century Hamburg became the European port of entry for many newly seen species. Aquaria became more widely popular as houses became almost universally electrified after World War I. With electricity great improvements were made in aquarium technology, allowing artificial lighting as well as the aeration, filtration, and heating of the water. Popularization was also assisted by the availability of air freight, which allowed a much wider variety of fish to be successfully imported from distant regions of origin that consequently attracted new hobbyists.

There are currently estimated to be about 60 million aquarium hobbyists worldwide, and many more aquaria kept by them. The hobby has the strongest following in Europe, Asia, and North America. In the United States, a large minority (40%) of aquarists maintain two or more tanks at any one time.

Function and design

From the outdoor ponds and glass jars of antiquity, modern aquaria have evolved into a wide range of specialized systems. Aquaria can vary in size from a small bowl large enough for a single small fish, to the huge public aquaria that can simulate entire marine ecosystems. The most successful aquaria, as judged by the long-term survivability of its inhabitants, carefully emulate the natural environments that their residents would occupy in the wild.

Freshwater aquaria remain the most popular due to their lower cost and easier maintenance, but marine (saltwater) aquaria have gained cachet as dedicated enthusiasts prove it is possible to preserve these challenging environments.

Design

Filtration system in a typical aquarium: (1) Intake. (2) Mechanical filtration. (3) Chemical filtration. (4) Biological filtration medium. (5) Outflow to tank.

The common freshwater aquarium maintained by a home aquarist typically includes a filtration system, an artificial lighting system, air pumps, and a heater. In addition, some freshwater tanks (and most saltwater tanks) use powerheads to increase water circulation.

Combined biological and mechanical filtration systems are now common; these are designed to remove potentially dangerous build up of nitrogenous wastes and phosphates dissolved in the water, as well as particulate matter. Filtration systems are the most complexly engineered component of most home aquaria, and various designs are used. Most systems use pumps to remove a small portion of the tank's water to an external pathway where filtration occurs; the filtered water is then returned to the aquarium. Protein skimmers, filtration devices that remove proteins and other waste from the water, are usually found only in salt water aquaria.

Air pumps are employed to adequately oxygenate (or in the case of a heavily planted aquarium, provide carbon dioxide to) the water. These devices, once universal, are now somewhat less commonly used as some newer filtration systems create enough surface agitation to supply adequate gas exchange at the surface. Aquarium heaters are designed to act as thermostats to regulate water temperature at a level designated by the aquarist when the prevailing temperature of air surrounding the aquarium is below the desired water temperature. Coolers are also available for use in cold water aquaria or in parts of the world where the ambient room temperature is above the desired tank temperature.

An aquarium's physical characteristics form another aspect of aquarium design. Size, lighting conditions, density of floating and rooted plants, placement of bogwood, creation of caves or overhangs, type of substrate, and other factors (including an aquarium's positioning within a room) can all affect the behavior and survivability of tank inhabitants.

The combined function of these elements is to maintain appropriate water quality and characteristics suitable for the aquarium's residents.

Classifications

Aquaria can be classified by several variables that determine the type of aquatic life that can be suitably housed. The conditions and characteristics of the water contained in an aquarium are the most important classification criteria, as most aquatic life will not survive even limited exposure to unsuitable water conditions. The size of an aquarium also limits the aquarist in what types of ecosystems he can reproduce, species selection, and biological loading.

Water conditions

A saltwater aquarium

The dissolved content of water is perhaps the most important aspect of water conditions, as dissolved salts and other constituents can dramatically impact basic water chemistry, and therefore how organisms are able to interact with their environment. Salt content, or salinity, is the most basic classification of water conditions. An aquarium may have fresh water (a salt level of < 0.5%), simulating a lake or river environment; salt water (a salt level of 5%–18%), simulating an ocean or sea environment; or brackish water (a salt level of 0.5%–5%), simulating environments lying between fresh and salt, such as estuaries.

Several other water characteristics result from dissolved contents of the water, and are important to the proper simulation of natural environments. The pH of the water is a measure of alkalinity or acidity. Hardness measures overall dissolved mineral content; soft or hard water may be preferred. Dissolved organic content and dissolved gases content are also important factors.

Home aquarists typically use modified tap water supplied through their local municipal water system to fill their tanks. For freshwater aquaria, additives formulated to remove chlorine or chloramine (used to disinfect drinking water supplies for human consumption) are often all that is needed to make the water ready for aquarium use. Brackish or saltwater aquaria require the addition of a mixture of salts and other minerals, which are commercially available for this purpose. More sophisticated aquarists may make other modifications to their base water source to modify the water's alkalinity, hardness, or dissolved content of organics and gases, before adding it to their aquaria. In contrast, public aquaria with large water needs often locate themselves near a natural water source (such as a river, lake, or ocean) in order to have easy access to large volumes of water that does not require much further treatment.

Secondary water characteristics

Secondary water characteristics are also important to the success of an aquarium. The temperature of the water forms the basis of one of the two most basic aquarium classifications: tropical vs. cold water. Most fish and plant species tolerate only a limited range of water temperatures: Tropical or warm water aquaria, with an average temperature of about 25 °C (78 °F), are much more common and house most popular aquarium fish. Cold water aquaria are those with temperatures below what would be considered tropical; a variety of fish are better suited to this cooler environment.

Water movement can also be important in accurately simulating a natural ecosystem. Aquarists may prefer anything from still water up to swift simulated currents in an aquarium, depending on the conditions best suited for the aquarium's inhabitants.

Water temperature can be regulated with a combined thermometer/heater unit (or, more rarely, with a cooling unit), while water movement can be controlled through the use of powerheads and careful design of internal water flow (such as location of filtration system points of inflow and outflow).

Size

Simple hobbyist Aquarium, 80 x 30 x 40 cm, 96 liter

An aquarium can range from a small, unadorned glass bowl containing less than a liter of water – although generally unsuited for most fish (except, perhaps, air breathing fish such as Betta splendens or the Paradise Fish) – to massive tanks built in public aquaria which are limited only by engineering constraints and can house entire ecosystems as large as kelp forests or species of large sharks. In general, larger aquarium systems are typically recommended to hobbyists due to their resistance to rapid fluctuations of temperature and pH, allowing for greater system stability.

Aquaria kept in homes by hobbyists can be as small as 3 U.S. gallons (11 L). This size is widely considered the smallest practical system with filtration and other basic systems; indeed, the local government of Rome has recently taken the step of banning traditional goldfish bowls as inhumane. Practical limitations, most notably the weight (water weighs about 8.3 pounds per U.S. gallon (1 kg/L)) and internal water pressure (requiring thick, strong glass siding) of a large aquarium, keep most home aquaria to a maximum of around 1 m³ (300 U.S. gallons). However, some dedicated aquarists have been known to construct custom aquaria of up to several thousand U.S. gallons (several cubic meters), at great effort and expense.

Public aquaria designed for exhibition of large species or environments can be dramatically larger than any home aquarium. The Shedd Aquarium features an individual aquarium of two million U.S. gallons (7,500 m³), as well as two others of 400,000 U.S. gallons (1,500 m³). The Monterey Bay Aquarium has an acrylic viewing window into their largest tank. At 56 feet long by 17 feet high (17 by 5 m), it used to be the largest window in the world and is over 13 inches (330 mm) thick. The Okinawa Churaumi Aquarium is the world's second largest aquarium and part of the Ocean Expo Park located in Motobu, Okinawa. Its main tank, which holds 7,500 cubic meters of water, features the world's largest acrylic panel measuring 8.2 meters by 22.5 meters with a thickness of 60 centimeters. The size of public aquaria are usually limited by cost considerations.

Species selection

Several theories on species selection circulate within the community of hobby aquarists. Perhaps the most popular of these is the division of aquaria into either a community or aggressive tank type. Community tanks house several species that are not aggressive toward each other. This is the most common type of hobby aquarium kept today. Aggressive tanks, in contrast, house a limited number of species that can be aggressive toward other fish, or are able to withstand aggression well. In both of these tank types, the aquarium cohabitants may or may not originate from the same geographic region, but generally tolerate similar water conditions. In addition to the fish, invertebrates, plants, and decorations or "aquarium furniture" (all of which may or may not be natural neighbors of any of the fish) are typically added to these tank types.

Species or specimen tanks usually only house one fish species, along with plants, perhaps found in the fishes' natural environment and decorations simulating a true ecosystem. These tanks are often used for killifish, livebearers, cichlids etc. They can be simple as bare bottom with a few necessities or a complex planted aquarium. Some tanks of this sort are used simply to house adults for breeding. Such tanks are common in fishrooms, where people keep many tanks at home.

Ecotype or ecotope aquaria attempt to simulate a specific ecosystem found in the natural world, bringing together fish, invertebrate species, and plants found in that ecosystem in a tank with water conditions and decorations designed to simulate their natural environment. These ecotype aquaria might be considered the most sophisticated hobby aquaria; indeed, reputable public aquaria all use this approach in their exhibits whenever possible. This approach best simulates the experience of observing an aquarium's inhabitants in the wild, and also usually serves as the healthiest possible artificial environment for the tank's occupants.

Species selection for saltwater aquaria

In addition to the types above, a special category of saltwater aquaria is the reef aquarium. These aquaria attempt to simulate the complex reef ecosystems found in warm, tropical oceans around the world. These aquaria focus on the rich diversity of invertebrate life in these environments, and typically include only a limited number of small fish. Techniques of maintaining sea anemones, some corals, live rock, mollusks, and crustacea, developed since the 1980s, have made the recreations of a reef ecosystem possible. Reef aquaria are widely considered the most difficult and demanding of the common hobbyist aquarium types, requiring the most expertise in addition to the most specialized equipment (and corresponding high cost).

Source of aquarium inhabitants

A surface supplied diver interacts with viewers while feeding the fish

Fish and plants for the first modern aquaria were gathered from the wild and transported (usually by ship) to European and American ports. During the early twentieth century many species of small colorful tropical fish were caught and exported from Manaus Brazil, Bangkok Thailand, Siam, Jakarta Indonesia, the Dutch West Indies, Calcutta India, and other tropical ports. Collection of fish, plants, and invertebrates from the wild for supply to the aquarium trade continues today at locations around the world. In many places of the world, impoverished local villagers collect specimens for the aquarium trade as their prime means of income. It remains an important source for many species that have not been successfully bred in captivity, and continues to introduce new species to enthusiastic aquarists.

The practice of collection in the wild for eventual display in aquaria has several disadvantages. Collecting expeditions can be lengthy and costly, and are not always successful. The shipping process is very hazardous for the fish involved; mortality rates are high. Many others are weakened by stress and become diseased upon arrival. Fish can also be injured during the collection process itself, most notably during the process of using cyanide to stun reef fish to make them easier to collect.

More recently, the potentially detrimental environmental impact of fish and plant collecting has come to the attention of aquarists worldwide. These include the poisoning of coral reefs and non-target species, the depletion of rare species from their natural habitat, and the degradation of ecosystems from large scale removal of key species. Additionally, the destructive fishing techniques used have become a growing concern to environmentalists and hobbyists alike. Therefore, there has been a concerted movement by many concerned aquarists to reduce the trade's dependence on wild-collected specimens through captive breeding programs and certification programs for wild-caught fish. Among American keepers of marine aquaria surveyed in 1997, two thirds said that they prefer to purchase farm raised coral instead of wild-collected coral, and over 80% think that only sustainably caught or captive bred fish should be allowed for trade.

Since the 'fighting fish' Betta splendens was first successfully bred in France in 1893, captive spawning techniques have been slowly discovered. Captive breeding for the aquarium trade is now concentrated in South Florida, Singapore, Hong Kong, and Bangkok, with smaller industries in Hawaii and Sri Lanka. Captive breeding programs of marine organisms for the aquarium trade have been urgently in development since the mid-1990s. Breeding programs for freshwater species are comparatively more advanced than for saltwater species.

Aquaculture is the cultivation of aquatic organisms in a controlled environment. Supporters of aquaculture programs for supply to the aquarium trade claim that well-planned programs can bring benefits to the environment as well as the society around it. Aquaculture can help in lessening the impacts on wild stocks, either by using raised cultivated organisms directly for sale or by releasing them to replenish wild stock (Tlusty 203), although such a practice is associated with several environmental risks.

Ecology

Ideal aquarium ecology reproduces the equilibrium found in nature in the closed system of an aquarium. In practice it is virtually impossible to maintain a perfect balance. As an example, a balanced predator-prey relationship is nearly impossible to maintain in even the largest of aquaria. Typically an aquarium keeper must take steps to maintain equilibrium in the small ecosystem contained in his aquarium.

Approximate equilibrium is facilitated by large volumes of water. Any event that perturbs the system pushes an aquarium away from equilibrium; the more water that is contained in a tank, the easier such a systemic shock is to absorb, as the effects of that event are diluted. For example, the death of the only fish in a three U.S. gallon tank (11 L) causes dramatic changes in the system, while the death of that same fish in a 100 U.S. gallon (400 L) tank with many other fish in it represents only a minor change in the balance of the tank. For this reason, hobbyists often favor larger tanks when possible, as they are more stable systems requiring less intensive attention to the maintenance of equilibrium.

Nitrogen cycle

The nitrogen cycle in an aquarium.

Of primary concern to the aquarist is management of the biological waste produced by an aquarium's inhabitants. Fish, invertebrates, fungi, and some bacteria excrete nitrogen waste in the form of ammonia (which may convert to ammonium, depending on water chemistry) which must then pass through the nitrogen cycle. Ammonia is also produced through the decomposition of plant and animal matter, including fecal matter and other detritus. Nitrogen waste products become toxic to fish and other aquarium inhabitants at high concentrations.

A well-balanced tank contains organisms that are able to metabolize the waste products of other aquarium residents. The nitrogen waste produced in a tank is metabolized in aquaria by a type of bacteria known as nitrifiers (genus Nitrosomonas). Nitrifying bacteria capture ammonia from the water and metabolize it to produce nitrite. Nitrite is also highly toxic to fish in high concentrations. Another type of bacteria, genus Nitrospira, converts nitrite into nitrate, a less toxic substance to aquarium inhabitants. (Nitrobacter bacteria were previously believed to fill this role, and continue to be found in commercially available products sold as kits to "jump start" the nitrogen cycle in an aquarium. While biologically they could theoretically fill the same niche as Nitrospira, it has recently been found that Nitrobacter are not present in detectable levels in established aquaria, while Nitrospira are plentiful.) This process is known in the aquarium hobby as the nitrogen cycle.

In addition to bacteria, aquatic plants also eliminate nitrogen waste by metabolizing ammonia and nitrate. When plants metabolize nitrogen compounds, they remove nitrogen from the water by using it to build biomass. However, this is only temporary, as the plants release nitrogen back into the water when older leaves die off and decompose.

Although informally called the nitrogen cycle by hobbyists, it is in fact only a portion of a true cycle: nitrogen must be added to the system (usually through food provided to the tank inhabitants), and nitrates accumulate in the water at the end of the process (or contribute to a growth in biomass via plant metabolism). This accumulation of nitrates in home aquaria requires the aquarium keeper to remove water that is high in nitrates or remove plants which have grown from the nitrates. A balanced system, in which the fish eat the plants, is generally difficult to create.

Aquaria kept by hobbyists often do not have the requisite populations of bacteria needed to detoxify nitrogen waste from tank inhabitants. This problem is most often addressed through two filtration solutions: Activated carbon filters absorb nitrogen compounds and other toxins from the water, while biological filters provide a medium specially designed for colonization by the desired nitrifying bacteria.

Cycling

New aquaria also do not usually have the required populations of bacteria for the handling of nitrogen waste. In a process called cycling, aquarists cultivate these bacteria as fish and other producers of nitrogen waste are gradually added to the tank over the course of several weeks. Aquarists use several different methods to jump start this process, including the use of water additives containing small populations of the bacteria, or "seeding" a new tank with a mature bacterial colony removed from another aquarium (such as can be found on gravel or biological filter media).

Other cycling methods that have gained popularity in recent years are the fishless cycle and the silent cycle. As the name of the former implies, no fish are kept in a tank undergoing a fishless cycle. Instead, small amounts of ammonia are added to the tank to feed the bacteria being cultured. During this process, ammonia, nitrite, and nitrate levels are tested to monitor progress. The silent cycle is basically nothing more than densely stocking the aquarium with fast-growing aquatic plants and relying on them to consume the nitrogen products rather than bacteria. According to anecdotal reports of aquarists specializing in planted tanks, the plants can consume nitrogenous waste so efficiently that the spikes in ammonia and nitrite levels normally seen in more traditional cycling methods are greatly reduced, if they are detectable at all.

Improperly cycled aquaria can quickly accumulate toxic concentrations of nitrogen waste and kill its inhabitants.

Other nutrient cycles

Nitrogen is not the only nutrient that cycles through an aquarium. Dissolved oxygen enters the system at the surface water-air interface or through the actions of an air pump. Carbon dioxide escapes the system into the air. The phosphate cycle is an important, although often overlooked, nutrient cycle. Sulfur, iron, and micronutrients also cycle through the system, entering as food and exiting as waste. Appropriate handling of the nitrogen cycle, along with supplying an adequately balanced food supply and considered biological loading, is usually enough to keep these other nutrient cycles in approximate equilibrium.

Biological loading

Biological loading is a measure of the burden placed on the aquarium ecosystem by its living inhabitants. High biological loading in an aquarium represents a more complicated tank ecology, which in turn means that equilibrium is easier to perturb. In addition, there are several fundamental constraints on biological loading based on the size of an aquarium. The surface area of water exposed to air limits dissolved oxygen intake by the tank. The capacity of nitrifying bacteria is limited by the physical space they have available to colonize. Physically, only a limited size and number of plants and animals can be fit into an aquarium while still providing room for movement.

In order to prevent biological overloading of the system, aquarists have developed a number of rules of thumb. Perhaps the most popular of these is the "one inch of fish per U.S. gallon" rule, which dictates that the sum in inches of the lengths of all fish kept in an aquarium (excluding tail length) should not exceed the capacity of the tank measured in U.S. gallons (about 7 mm per liter of water). This rule is usually applied to the expected mature size of the fish, in order to not stunt growth by overcrowding, which can be unhealthy for the fish. For goldfish and other high-waste fish, some aquarists recommend doubling the space allowance to one inch of fish per every two gallons.

The true maximum or ideal biological loading of a system is very difficult to calculate, even on a theoretical level. To do so, the variables for waste production rate, nitrification efficiency, gas exchange rate at the water surface, and many others would need to be determined. In practice this is a very complicated and difficult task, and so most aquarists use rules of thumb combined with a trial and error approach to reach an appropriate level of biological loading.

Public aquaria

A 335,000 U.S. gallon (1.3 million liter) aquarium at the Monterey Bay Aquarium in California displaying a simulated kelp forest ecosystem

Public aquaria are facilities open to the public for viewing of aquatic species in aquaria. Most public aquaria feature a number of smaller tanks, as well as one or more large tank greater in size than could be kept by any home aquarist. The largest tanks hold millions of U.S. gallons of water and can house large species, including dolphins, sharks or beluga whales. Aquatic and semiaquatic animals, including otters and penguins, may also be kept by public aquaria.

Operationally, a public aquarium is similar in many ways to a zoo or museum. A good aquarium will have special exhibits to entice repeat visitors, in addition to its permanent collection. A few have their own version of a "petting zoo"; for instance, the Monterey Bay Aquarium has a shallow tank filled with common types of rays, and one can reach in to feel their leathery skins as they pass by.

Also as with zoos, aquaria usually have specialized research staff who study the habits and biology of their specimens. In recent years, the large aquaria have been attempting to acquire and raise various species of open-ocean fish, and even jellyfish (or sea-jellies, cnidaria), a difficult task since these creatures have never before encountered solid surfaces like the walls of a tank, and do not have the instincts to turn aside from the walls instead of running into them.

The first public aquarium opened in London's Regent's Park in 1853. P.T. Barnum quickly followed with the first American aquarium, opened on Broadway in New York. Following early examples of Detroit, New York and San Francisco, many major cities now have public aquaria. Most public aquaria are located close to the ocean, for a steady supply of natural seawater. An inland pioneer was Chicago's Shedd Aquarium that received seawater shipped by rail in special tank cars. In contrast, the recently opened Georgia Aquarium filled its tanks with fresh water from the city water system and salinated its salt water exhibits using the same commercial salt and mineral additives available to home aquarists.

In January 1985 Kelly Tarlton began construction of the first aquarium to include a large transparent acrylic tunnel in Auckland, New Zealand, a task that took 10 months and cost NZ$3 million. The 110-meter tunnel was built from one-tonne slabs of German sheet plastic that were shaped locally in an oven. A moving walkway now transports visitors through, and groups of school children occasionally hold sleepovers there beneath the swimming sharks and rays.

Top public aquaria are often affiliated with important oceanographic research institutions or conduct their own research programs, and usually (though not always) specialize in species and ecosystems that can be found in local waters.

For a partial list of public aquaria worldwide, see list of aquaria.


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For a partial list of public aquaria worldwide, see list of aquaria. This property can be seen in the University of Queensland's pitch drop experiment, where each drop has taken approximately 10 years to fall into the beaker. Top public aquaria are often affiliated with important oceanographic research institutions or conduct their own research programs, and usually (though not always) specialize in species and ecosystems that can be found in local waters. Note that pitch, another seemingly-solid material, is in fact a highly viscous liquid, 100 billion times as viscous as water. A moving walkway now transports visitors through, and groups of school children occasionally hold sleepovers there beneath the swimming sharks and rays. Occasionally such glass has been found thinner side down, as would be caused by carelessness at the time of installation. The 110-meter tunnel was built from one-tonne slabs of German sheet plastic that were shaped locally in an oven. When actually installed in a window frame, the glass would be placed thicker side down for the sake of stability and visual sparkle.

In January 1985 Kelly Tarlton began construction of the first aquarium to include a large transparent acrylic tunnel in Auckland, New Zealand, a task that took 10 months and cost NZ$3 million. The pieces were not, however, absolutely flat; the edges of the disk would be thicker because of centripetal forces. In contrast, the recently opened Georgia Aquarium filled its tanks with fresh water from the city water system and salinated its salt water exhibits using the same commercial salt and mineral additives available to home aquarists. This plate was then cut to fit a window. An inland pioneer was Chicago's Shedd Aquarium that received seawater shipped by rail in special tank cars. The likely source of this belief is that when panes of glass were commonly made by glassblowers, the technique that was used was to spin molten glass so as to create a round, mostly flat and even plate (the Crown glass process, described above). Most public aquaria are located close to the ocean, for a steady supply of natural seawater. It is then assumed that the glass was once uniform, but has flowed to its new shape.

Following early examples of Detroit, New York and San Francisco, many major cities now have public aquaria. Supporting evidence that is often offered is that old windows are often thicker at the bottom than at the top. Barnum quickly followed with the first American aquarium, opened on Broadway in New York. One common misconception is that glass is a super-cooled liquid of practically infinite viscosity when at room temperature. P.T. See also Window. The first public aquarium opened in London's Regent's Park in 1853. These glass types can be further utilised by the following processes:.

In recent years, the large aquaria have been attempting to acquire and raise various species of open-ocean fish, and even jellyfish (or sea-jellies, cnidaria), a difficult task since these creatures have never before encountered solid surfaces like the walls of a tank, and do not have the instincts to turn aside from the walls instead of running into them. Several methods of producing glass for applications have been developed, including:. Also as with zoos, aquaria usually have specialized research staff who study the habits and biology of their specimens. Foamed glass, made from waste glass, can be used as lightweight, closed-cell insulation. A few have their own version of a "petting zoo"; for instance, the Monterey Bay Aquarium has a shallow tank filled with common types of rays, and one can reach in to feel their leathery skins as they pass by. Glass fibre insulation is common in roofs and walls. A good aquarium will have special exhibits to entice repeat visitors, in addition to its permanent collection. Glass in buildings can be of a safety type, including wired, toughened and laminated glasses.

Operationally, a public aquarium is similar in many ways to a zoo or museum. Typical uses for glass in buildings include as a transparent material for windows in the building envelope, as internal glazed partitions and as architectural features. Aquatic and semiaquatic animals, including otters and penguins, may also be kept by public aquaria. Glass has been used in buildings since the 11th century. gallons of water and can house large species, including dolphins, sharks or beluga whales. Main articles: Architectural Glass and Glazing. The largest tanks hold millions of U.S. Stained glass is an art form with a long history; many churches have beautiful stained-glass windows.

Most public aquaria feature a number of smaller tanks, as well as one or more large tank greater in size than could be kept by any home aquarist. See the Harvard Museum of Natural History's page on the exhibit for further information. Public aquaria are facilities open to the public for viewing of aquatic species in aquaria. The Blaschka Glass Flowers are still an inspiration to glassblowers today. In practice this is a very complicated and difficult task, and so most aquarists use rules of thumb combined with a trial and error approach to reach an appropriate level of biological loading. These were lampworked by Leopold Blaschka and his son Rudolph, who never revealed the method he used to make them. To do so, the variables for waste production rate, nitrification efficiency, gas exchange rate at the water surface, and many others would need to be determined. The Harvard Museum of Natural History has a collection of extremely detailed models of flowers made of painted glass.

The true maximum or ideal biological loading of a system is very difficult to calculate, even on a theoretical level. A significant exception is the collection of pieces by the Blaschkas. For goldfish and other high-waste fish, some aquarists recommend doubling the space allowance to one inch of fish per every two gallons. Colored glass is often used, and sometimes the glass is painted, although many glassblowers consider this crude. This rule is usually applied to the expected mature size of the fish, in order to not stunt growth by overcrowding, which can be unhealthy for the fish. Objects made out of glass include vessels (bowls, vases, and other containers), paperweights, marbles, beads, smoking pipes, bongs, and sculptures. gallons (about 7 mm per liter of water). Glass can also be cut with a diamond saw, and polished to give gleaming facets.

gallon" rule, which dictates that the sum in inches of the lengths of all fish kept in an aquarium (excluding tail length) should not exceed the capacity of the tank measured in U.S. Glass that is manipulated in a kiln is called warm glass, and traditional stained glass work is commonly called cold glass work. Perhaps the most popular of these is the "one inch of fish per U.S. Someone who works with hot glass is called a glassblower or lampworker, and these techniques are how most fine glassware is created. In order to prevent biological overloading of the system, aquarists have developed a number of rules of thumb. There are many techniques for creating fine glass art; each is suitable for certain kinds of object and unsuitable for others. Physically, only a limited size and number of plants and animals can be fit into an aquarium while still providing room for movement. The term "crystal glass", derived from rock crystal, has come to denote high-grade colourless glass, often containing lead, and is sometimes applied to any fine hand-blown glass.

The capacity of nitrifying bacteria is limited by the physical space they have available to colonize. Some artists in glass include Lino Tagliapietra, Sidney Waugh, Rene Lalique, Dale Chihuly, and Louis Comfort Tiffany, who were responsible for extraordinary glass objects. The surface area of water exposed to air limits dissolved oxygen intake by the tank. Even with the availability of common glassware, hand blown or lampworked glassware remains popular for its artistry. In addition, there are several fundamental constraints on biological loading based on the size of an aquarium. Volcanic glasses, such as obsidian, have long been used to make stone tools, and flint knapping techniques can easily be adapted to mass-produced glass. High biological loading in an aquarium represents a more complicated tank ecology, which in turn means that equilibrium is easier to perturb. Most such glass is mass-produced using various industrial processes, but most large laboratories need so much custom glassware that they keep a glassblower on staff.

Biological loading is a measure of the burden placed on the aquarium ecosystem by its living inhabitants. For the most demanding applications, quartz glass is used, although it is very difficult to work. Appropriate handling of the nitrogen cycle, along with supplying an adequately balanced food supply and considered biological loading, is usually enough to keep these other nutrient cycles in approximate equilibrium. For these applications, borosilicate glass (such as Pyrex) is usually used for its strength and low coefficient of thermal expansion, which gives greater resistance to thermal shock and allows for greater accuracy in laboratory measurements when heating and cooling experiments. Sulfur, iron, and micronutrients also cycle through the system, entering as food and exiting as waste. In laboratories doing research in chemistry, biology, physics and many other fields, flasks, test tubes, lenses and other laboratory equipment are often made of glass. The phosphate cycle is an important, although often overlooked, nutrient cycle. Drinking glasses, bowls, and bottles are often made of glass, as are light bulbs, mirrors, the picture tubes of computer monitors and televisions, and windows.

Carbon dioxide escapes the system into the air. Many household objects are made of glass. Dissolved oxygen enters the system at the surface water-air interface or through the actions of an air pump. Since glass is strong and unreactive, it is a very useful material. Nitrogen is not the only nutrient that cycles through an aquarium. See also: Broad sheet, Blown plate, Polished plate, Cylinder blown sheet, Machine drawn cylinder sheet. Improperly cycled aquaria can quickly accumulate toxic concentrations of nitrogen waste and kill its inhabitants. This reduced manufacturing costs and, combined with a wider use of coloured glass, led to cheap popular glassware in the 1930s, which later became known as Depression glass.

According to anecdotal reports of aquarists specializing in planted tanks, the plants can consume nitrogenous waste so efficiently that the spikes in ammonia and nitrite levels normally seen in more traditional cycling methods are greatly reduced, if they are detectable at all. In the 1920s a new mould-etch process was invented, in which art was etched directly into the mould, so that each cast piece emerged from the mold with the image already on the surface of the glass. The silent cycle is basically nothing more than densely stocking the aquarium with fast-growing aquatic plants and relying on them to consume the nitrogen products rather than bacteria. Traditionally this was done by a trained artisan after the glass was blown or cast. During this process, ammonia, nitrite, and nitrate levels are tested to monitor progress. Art is sometimes etched into glass via acid or other caustic substance (causing the image to be eaten into the glass). Instead, small amounts of ammonia are added to the tank to feed the bacteria being cultured. Blenko in the 1920s.

As the name of the former implies, no fish are kept in a tank undergoing a fishless cycle. The cylinder method of creating flat glass was first used in the United States of America by William J. Other cycling methods that have gained popularity in recent years are the fishless cycle and the silent cycle. The invention of the glass pressing machine in 1827 allowed the mass production of inexpensive glass articles. Aquarists use several different methods to jump start this process, including the use of water additives containing small populations of the bacteria, or "seeding" a new tank with a mature bacterial colony removed from another aquarium (such as can be found on gravel or biological filter media). Around 1688, a process for casting glass was developed, which led to its becoming a much more commonly used material. In a process called cycling, aquarists cultivate these bacteria as fish and other producers of nitrogen waste are gradually added to the tank over the course of several weeks. Venetian glass was highly prized between the 10th and 14th centuries as they managed to keep the process secret.

New aquaria also do not usually have the required populations of bacteria for the handling of nitrogen waste. The disk would then be cut into panes. This problem is most often addressed through two filtration solutions: Activated carbon filters absorb nitrogen compounds and other toxins from the water, while biological filters provide a medium specially designed for colonization by the desired nitrifying bacteria. In this process, the glassblower would spin around 9 lb (4 kg) of molten glass at the end of a rod until it flattened into a disk approximately 5 ft (1.5 m) in diameter. Aquaria kept by hobbyists often do not have the requisite populations of bacteria needed to detoxify nitrogen waste from tank inhabitants. The Crown glass process was used up to the mid-1800s. A balanced system, in which the fish eat the plants, is generally difficult to create. Eventually some of the Venetian glass workers moved to other areas of northern Europe and glass making spread with them.

This accumulation of nitrates in home aquaria requires the aquarium keeper to remove water that is high in nitrates or remove plants which have grown from the nitrates. The centre for glass making from the 14th century was Venice, which developed many new techniques and became the centre of a lucrative export trade in dinner ware, mirrors, and other luxury items. Although informally called the nitrogen cycle by hobbyists, it is in fact only a portion of a true cycle: nitrogen must be added to the system (usually through food provided to the tank inhabitants), and nitrates accumulate in the water at the end of the process (or contribute to a growth in biomass via plant metabolism). Until the 12th century, stained glass (i.e., glass with some colouring impurities, usually metals) was not widely used. However, this is only temporary, as the plants release nitrogen back into the water when older leaves die off and decompose. This technique was perfected in 13th century Venice. When plants metabolize nitrogen compounds, they remove nitrogen from the water by using it to build biomass. The 11th century saw the emergence, in Germany, of new ways of making sheet glass by blowing spheres, swinging these out to form cylinders, cutting these while still hot, and then flattening the sheets.

In addition to bacteria, aquatic plants also eliminate nitrogen waste by metabolizing ammonia and nitrate. From this point on, northern glass differed significantly from that made in the Mediterranean area, where soda remained in common use. While biologically they could theoretically fill the same niche as Nitrospira, it has recently been found that Nitrobacter are not present in detectable levels in established aquaria, while Nitrospira are plentiful.) This process is known in the aquarium hobby as the nitrogen cycle. About 1000 AD, an important technical breakthrough was made in Northern Europe when soda glass was replaced by glass made from a much more readily available material: potash obtained from wood ashes. (Nitrobacter bacteria were previously believed to fill this role, and continue to be found in commercially available products sold as kits to "jump start" the nitrogen cycle in an aquarium. These form an important link between Roman times and the later importance of that city in the production of the material. Another type of bacteria, genus Nitrospira, converts nitrite into nitrate, a less toxic substance to aquarium inhabitants. Glass objects from the 7th and 8th centuries have been found on the island of Torcello near Venice.

Nitrite is also highly toxic to fish in high concentrations. When gem-cutters learned to cut glass, they found clear glass was an excellent refractor of light, the popularity of cut clear glass soared, that of coloured glass diminished. Nitrifying bacteria capture ammonia from the water and metabolize it to produce nitrite. Glassmakers learned to make coloured glass by adding metallic compounds and mineral oxides to produce brilliant hues of red, green, and blue - the colours of gemstones. The nitrogen waste produced in a tank is metabolized in aquaria by a type of bacteria known as nitrifiers (genus Nitrosomonas). Common glass today usually has a slight green or blue tint, arising from these same impurities. A well-balanced tank contains organisms that are able to metabolize the waste products of other aquarium residents. This colour is caused by the varying amounts of naturally occurring iron impurities in the sand.

Nitrogen waste products become toxic to fish and other aquarium inhabitants at high concentrations. The colour of "natural glass" is green to bluish green. Ammonia is also produced through the decomposition of plant and animal matter, including fecal matter and other detritus. This was the discovery of glassblowing, both free-blowing and mould-blowing. Fish, invertebrates, fungi, and some bacteria excrete nitrogen waste in the form of ammonia (which may convert to ammonium, depending on water chemistry) which must then pass through the nitrogen cycle. In the first century BC, somewhere at the eastern end of the Mediterranean, a new invention caused a true revolution in the glass industry. Of primary concern to the aquarist is management of the biological waste produced by an aquarium's inhabitants. As time passed, it was discovered (most likely by a potter) that if glass is heated until it becomes semi-liquid, it can be shaped and left to cool in a new, solid, independently standing shape.

For this reason, hobbyists often favor larger tanks when possible, as they are more stable systems requiring less intensive attention to the maintenance of equilibrium. Small pieces of coloured glass were considered valuable and often rivalled precious gems as jewellery items. gallon (400 L) tank with many other fish in it represents only a minor change in the balance of the tank. The earliest use of glass was as a coloured, opaque, or transparent glaze applied to ceramics before they were fired. gallon tank (11 L) causes dramatic changes in the system, while the death of that same fish in a 100 U.S. Glass was made from sand, plant ash and lime. For example, the death of the only fish in a three U.S. During the Roman Empire many forms of glass were created, usually for vases and bottles.

Any event that perturbs the system pushes an aquarium away from equilibrium; the more water that is contained in a tank, the easier such a systemic shock is to absorb, as the effects of that event are diluted. In the first century BC the technique of blowing glass was developed and what had once been an extremely rare and valuable item became much more common. Approximate equilibrium is facilitated by large volumes of water. Glass making instructions were first documented in Egypt around 1500 BC, when glass was used as a glaze for pottery and other items. Typically an aquarium keeper must take steps to maintain equilibrium in the small ecosystem contained in his aquarium. Naturally occurring glass, such as obsidian, has been used since the stone age. As an example, a balanced predator-prey relationship is nearly impossible to maintain in even the largest of aquaria. New coloured glasses are frequently discovered.

In practice it is virtually impossible to maintain a perfect balance. The chemistry involved is complex and not well understood. Ideal aquarium ecology reproduces the equilibrium found in nature in the closed system of an aquarium. The way the glass is heated and cooled can significantly affect the colors produced by these compounds. Aquaculture can help in lessening the impacts on wild stocks, either by using raised cultivated organisms directly for sale or by releasing them to replenish wild stock (Tlusty 203), although such a practice is associated with several environmental risks. Silver compounds (notably silver nitrate) can produce a range of colors from orange-red to yellow. Supporters of aquaculture programs for supply to the aquarium trade claim that well-planned programs can bring benefits to the environment as well as the society around it. Uranium glass is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic.

Aquaculture is the cultivation of aquatic organisms in a controlled environment. Uranium (0.1 to 2%) can be added to give glass a fluorescent yellow or green colour. Breeding programs for freshwater species are comparatively more advanced than for saltwater species. Metallic gold, in very small concentrations (around 0.001%), produces a rich ruby-coloured glass, while lower concentrations produces a less intense red, often marketed as "cranberry". Captive breeding programs of marine organisms for the aquarium trade have been urgently in development since the mid-1990s. Adding titanium produces yellowish-brown glass. Captive breeding for the aquarium trade is now concentrated in South Florida, Singapore, Hong Kong, and Bangkok, with smaller industries in Hawaii and Sri Lanka. Nickel, depending on the concentration, produces blue, or violet, or even black glass.

Since the 'fighting fish' Betta splendens was first successfully bred in France in 1893, captive spawning techniques have been slowly discovered. Pure metallic copper produces a very dark red, opaque glass, which is sometimes used as a substitute for gold in the production of ruby-coloured glass. Among American keepers of marine aquaria surveyed in 1997, two thirds said that they prefer to purchase farm raised coral instead of wild-collected coral, and over 80% think that only sustainably caught or captive bred fish should be allowed for trade. 2 to 3% of copper oxide produces a turquoise colour. Therefore, there has been a concerted movement by many concerned aquarists to reduce the trade's dependence on wild-collected specimens through captive breeding programs and certification programs for wild-caught fish. Tin oxide with antimony and arsenic oxides produce an opaque white glass, first used in Venice to produce an imitation porcelain. Additionally, the destructive fishing techniques used have become a growing concern to environmentalists and hobbyists alike. Small concentrations of cobalt (0.025 to 0.1%) yield blue glass.

These include the poisoning of coral reefs and non-target species, the depletion of rare species from their natural habitat, and the degradation of ecosystems from large scale removal of key species. Like manganese, selenium can be used in small concentrations to decolorize glass, or in higher concentrations to impart a reddish colour. More recently, the potentially detrimental environmental impact of fish and plant collecting has come to the attention of aquarists worldwide. Manganese can be added in small amounts to remove the green tint lent by iron, or in higher concentrations to give glass an amethyst colour. Fish can also be injured during the collection process itself, most notably during the process of using cyanide to stun reef fish to make them easier to collect. Metals and metal oxides are added to glass during its manufacture to change its colour. Many others are weakened by stress and become diseased upon arrival. sol gel is a good example of glass prepared in this way.

The shipping process is very hazardous for the fish involved; mortality rates are high. By polymerizing glass it is possible to embed active molecules, such as enzymes, to add a new level of functionality to the glass vessels. Collecting expeditions can be lengthy and costly, and are not always successful. Putting in additives that modify the properties of glass is problematic, because the high temperature of preparation destroys most of them. The practice of collection in the wild for eventual display in aquaria has several disadvantages. An innovative way for making glass involves preparation by polymerization. It remains an important source for many species that have not been successfully bred in captivity, and continues to introduce new species to enthusiastic aquarists. Large amounts of iron are used in glass that absorbs infrared energy, such as heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths (biologically damaging ionizing radiation).

In many places of the world, impoverished local villagers collect specimens for the aquarium trade as their prime means of income. Thorium oxide gives glass a high refractive index and low dispersion, and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern glasses. Collection of fish, plants, and invertebrates from the wild for supply to the aquarium trade continues today at locations around the world. Adding barium also increases the refractive index. During the early twentieth century many species of small colorful tropical fish were caught and exported from Manaus Brazil, Bangkok Thailand, Siam, Jakarta Indonesia, the Dutch West Indies, Calcutta India, and other tropical ports. Lead glass, such as lead crystal or flint glass, is more 'brilliant' because the increased refractive index causes noticeably more "sparkles", while boron may be added to change the thermal and electrical properties, as in Pyrex. Fish and plants for the first modern aquaria were gathered from the wild and transported (usually by ship) to European and American ports. As well as soda and lime, most common glass has other ingredients added to change its properties.

Reef aquaria are widely considered the most difficult and demanding of the common hobbyist aquarium types, requiring the most expertise in addition to the most specialized equipment (and corresponding high cost). Soda-lime glasses account for about 90% of manufactured glass. Techniques of maintaining sea anemones, some corals, live rock, mollusks, and crustacea, developed since the 1980s, have made the recreations of a reef ecosystem possible. The resulting glass contains about 70% silica and is called a soda-lime glass. These aquaria focus on the rich diversity of invertebrate life in these environments, and typically include only a limited number of small fish. However, the soda makes the glass water-soluble, which is obviously undesirable, so lime (calcium oxide, CaO) is the third component, added to restore insolubility. These aquaria attempt to simulate the complex reef ecosystems found in warm, tropical oceans around the world. One is soda (sodium carbonate Na2CO3), or potash, the equivalent potassium compound, which lowers the melting point to about 1000 °C (1800 °F).

In addition to the types above, a special category of saltwater aquaria is the reef aquarium. Pure silica (SiO2) has a melting point of about 2000 °C (3600 °F), and while it can be made into glass for special applications (see fused quartz), two other substances are always added to common glass to simplify processing. This approach best simulates the experience of observing an aquarium's inhabitants in the wild, and also usually serves as the healthiest possible artificial environment for the tank's occupants. Collecting obsidian from national parks and some places may be prohibited by law, but the same toolmaking techniques can be applied to industrially-made glass. These ecotype aquaria might be considered the most sophisticated hobby aquaria; indeed, reputable public aquaria all use this approach in their exhibits whenever possible. Obsidian is a raw material for flint knappers, who have used it to make extremely sharp knives since the stone age. Ecotype or ecotope aquaria attempt to simulate a specific ecosystem found in the natural world, bringing together fish, invertebrate species, and plants found in that ecosystem in a tank with water conditions and decorations designed to simulate their natural environment. This glass is called obsidian, and is usually black with impurities.

Such tanks are common in fishrooms, where people keep many tanks at home. Glass is sometimes created naturally from volcanic magma. Some tanks of this sort are used simply to house adults for breeding. The glasses are arranged by composition, refractive index, and Abbe number. They can be simple as bare bottom with a few necessities or a complex planted aquarium. For example, BK7 is a low-dispersion borosilicate crown glass, and SF10 is a high-dispersion dense flint glass. These tanks are often used for killifish, livebearers, cichlids etc. Glasses used for making optical devices are commonly categorized using a six-digit glass code, or alternatively a letter-number code from the Schott Glass catalogue.

Species or specimen tanks usually only house one fish species, along with plants, perhaps found in the fishes' natural environment and decorations simulating a true ecosystem. Amorphous SiO2 is also used as a dielectric material in integrated circuits, due to the smooth and electrically neutral interface it forms with silicon. In addition to the fish, invertebrates, plants, and decorations or "aquarium furniture" (all of which may or may not be natural neighbors of any of the fish) are typically added to these tank types. Undersea cables have sections doped with erbium, which amplify transmitted signals by laser emission from within the glass itself. In both of these tank types, the aquarium cohabitants may or may not originate from the same geographic region, but generally tolerate similar water conditions. Individual fibres are given an equally transparent core of SiO2/GeO2 glass, which has only slightly different optical properties (the germanium contributing to a higher index of refraction). Aggressive tanks, in contrast, house a limited number of species that can be aggressive toward other fish, or are able to withstand aggression well. This type of glass can be made so pure that hundreds of kilometres of glass are transparent at infrared wavelengths in fibre optic cables.

This is the most common type of hobby aquarium kept today. Pure SiO2 glass (also called fused quartz) does not absorb UV light and is used for applications that require transparency in this region, although it is more expensive. Community tanks house several species that are not aggressive toward each other. This is due to the addition of compounds such as soda ash (sodium carbonate). Perhaps the most popular of these is the division of aquaria into either a community or aggressive tank type. Ordinary glass does not allow light at a wavelength of lower than 400 nm, also known as ultraviolet light or UV, to pass. Several theories on species selection circulate within the community of hobby aquarists. The transparency is due to an absence of electronic transition states in the range of visible light, and to the fact that such glass is homogeneous on all length scales greater than about a wavelength of visible light (inhomogeneities cause light to be scattered, breaking up any coherent image transmission).

The size of public aquaria are usually limited by cost considerations. One of the most obvious characteristics of ordinary glass is that it is transparent to visible light (not all glassy materials are). Its main tank, which holds 7,500 cubic meters of water, features the world's largest acrylic panel measuring 8.2 meters by 22.5 meters with a thickness of 60 centimeters. Common glass contains about 70% amorphous silicon dioxide (SiO2), which is the same chemical compound found in quartz, and its polycrystalline form, sand. The Okinawa Churaumi Aquarium is the world's second largest aquarium and part of the Ocean Expo Park located in Motobu, Okinawa. These properties can be modified, or even changed entirely, with the addition of other compounds or heat treatment. At 56 feet long by 17 feet high (17 by 5 m), it used to be the largest window in the world and is over 13 inches (330 mm) thick. Glass is, however, brittle and will break into sharp shards.

The Monterey Bay Aquarium has an acrylic viewing window into their largest tank. These desirable properties lead to a great many uses of glass. gallons (1,500 m³). In its pure form, glass is a transparent, relatively strong, hard-wearing, essentially inert, and biologically inactive material which can be formed with very smooth and impervious surfaces. gallons (7,500 m³), as well as two others of 400,000 U.S. The remainder of this article will be concerned with a specific type of glass—the silica-based glasses in common use as a building, container or decorative material. The Shedd Aquarium features an individual aquarium of two million U.S. The term enamel is used to describe glass fused as a decorative or functional coating on metal.

Public aquaria designed for exhibition of large species or environments can be dramatically larger than any home aquarium. Germanic tribes used the word glaes to describe amber, recorded by Roman historians as glaesum. Anglo-Saxons used the word glaer for amber. gallons (several cubic meters), at great effort and expense. glaes. However, some dedicated aquarists have been known to construct custom aquaria of up to several thousand U.S. glas, A.S. gallons). The word glass comes from Latin glacies (ice) and corresponds to German Glas, M.E.

gallon (1 kg/L)) and internal water pressure (requiring thick, strong glass siding) of a large aquarium, keep most home aquaria to a maximum of around 1 m³ (300 U.S. The resulting solid is amorphous, not crystalline like the sugar was originally, which can be seen in its conchoidal fracture. Practical limitations, most notably the weight (water weighs about 8.3 pounds per U.S. A simple example is when table sugar is melted and cooled rapidly by dumping the liquid sugar onto a cold surface. This size is widely considered the smallest practical system with filtration and other basic systems; indeed, the local government of Rome has recently taken the step of banning traditional goldfish bowls as inhumane. The materials definition of a glass is a uniform amorphous solid material, usually produced when a suitably viscous molten material cools very rapidly to below its glass transition temperature, thereby not giving enough time for a regular crystal lattice to form. gallons (11 L). .

Aquaria kept in homes by hobbyists can be as small as 3 U.S. This (along with chromatic aberration and other effects) limits the size of refracting telescopes, with the largest refractor in the World being the Yerkes Observatory telescope with a diameter of 102cm. In general, larger aquarium systems are typically recommended to hobbyists due to their resistance to rapid fluctuations of temperature and pH, allowing for greater system stability. The result is a loss of focus and is sometimes argued to occur not because of the liquid properties of glass but rather sagging of the telescope itself, but this is not correct. An aquarium can range from a small, unadorned glass bowl containing less than a liter of water – although generally unsuited for most fish (except, perhaps, air breathing fish such as Betta splendens or the Paradise Fish) – to massive tanks built in public aquaria which are limited only by engineering constraints and can house entire ecosystems as large as kelp forests or species of large sharks. This sag happens because the lens is only supported around its edge. Water temperature can be regulated with a combined thermometer/heater unit (or, more rarely, with a cooling unit), while water movement can be controlled through the use of powerheads and careful design of internal water flow (such as location of filtration system points of inflow and outflow). Glass in Refracting Telescopes, with objective lenses greater than 105cm in diameter, is observed to sag under its own under weight over time.

Aquarists may prefer anything from still water up to swift simulated currents in an aquarium, depending on the conditions best suited for the aquarium's inhabitants. Similarly, it should not be possible to see Newton's rings between decade-old fragments of window glass—but this can in fact be quite easily done. Water movement can also be important in accurately simulating a natural ecosystem. If glass flows at a rate that allows changes to be seen with the naked eye after centuries, then changes in optical telescope mirrors should be observable (by interferometry) in a matter of days—but this also is not observed. Cold water aquaria are those with temperatures below what would be considered tropical; a variety of fish are better suited to this cooler environment. If medieval glass has flowed perceptibly, then ancient Roman and Egyptian objects should have flowed proportionately more—but this is not observed. Most fish and plant species tolerate only a limited range of water temperatures: Tropical or warm water aquaria, with an average temperature of about 25 °C (78 °F), are much more common and house most popular aquarium fish. In layperson's terms, he wrote that glass at room temperature is very strongly on the solid side of the spectrum from solids to liquids.

cold water. Phys, 66(5):392-5, May 1998). The temperature of the water forms the basis of one of the two most basic aquarium classifications: tropical vs. J. Secondary water characteristics are also important to the success of an aquarium. Hence, the relaxation period (characteristic flow time) of cathedral glasses would be even longer" (Am. In contrast, public aquaria with large water needs often locate themselves near a natural water source (such as a river, lake, or ocean) in order to have easy access to large volumes of water that does not require much further treatment. Zanotto states "...the predicted relaxation time for GeO2 at room temperature is 1032 years.

More sophisticated aquarists may make other modifications to their base water source to modify the water's alkalinity, hardness, or dissolved content of organics and gases, before adding it to their aquaria. Writing in the American Journal of Physics, physicist Edgar D. Brackish or saltwater aquaria require the addition of a mixture of salts and other minerals, which are commercially available for this purpose. double-glazing. For freshwater aquaria, additives formulated to remove chlorine or chloramine (used to disinfect drinking water supplies for human consumption) are often all that is needed to make the water ready for aquarium use. application of a self-cleaning catylist. Home aquarists typically use modified tap water supplied through their local municipal water system to fill their tanks. chemical strengthening.

Dissolved organic content and dissolved gases content are also important factors. toughening. Hardness measures overall dissolved mineral content; soft or hard water may be preferred. laminating. The pH of the water is a measure of alkalinity or acidity. figure rolled glass. Several other water characteristics result from dissolved contents of the water, and are important to the proper simulation of natural environments. float (annealed) glass.

An aquarium may have fresh water (a salt level of < 0.5%), simulating a lake or river environment; salt water (a salt level of 5%–18%), simulating an ocean or sea environment; or brackish water (a salt level of 0.5%–5%), simulating environments lying between fresh and salt, such as estuaries. polished plate glass. Salt content, or salinity, is the most basic classification of water conditions. rolled plate glass. The dissolved content of water is perhaps the most important aspect of water conditions, as dissolved salts and other constituents can dramatically impact basic water chemistry, and therefore how organisms are able to interact with their environment. sheet glass. The size of an aquarium also limits the aquarist in what types of ecosystems he can reproduce, species selection, and biological loading. cylinder glass.

The conditions and characteristics of the water contained in an aquarium are the most important classification criteria, as most aquatic life will not survive even limited exposure to unsuitable water conditions. Aquaria can be classified by several variables that determine the type of aquatic life that can be suitably housed. The combined function of these elements is to maintain appropriate water quality and characteristics suitable for the aquarium's residents. Size, lighting conditions, density of floating and rooted plants, placement of bogwood, creation of caves or overhangs, type of substrate, and other factors (including an aquarium's positioning within a room) can all affect the behavior and survivability of tank inhabitants.

An aquarium's physical characteristics form another aspect of aquarium design. Coolers are also available for use in cold water aquaria or in parts of the world where the ambient room temperature is above the desired tank temperature. Aquarium heaters are designed to act as thermostats to regulate water temperature at a level designated by the aquarist when the prevailing temperature of air surrounding the aquarium is below the desired water temperature. These devices, once universal, are now somewhat less commonly used as some newer filtration systems create enough surface agitation to supply adequate gas exchange at the surface.

Air pumps are employed to adequately oxygenate (or in the case of a heavily planted aquarium, provide carbon dioxide to) the water. Protein skimmers, filtration devices that remove proteins and other waste from the water, are usually found only in salt water aquaria. Most systems use pumps to remove a small portion of the tank's water to an external pathway where filtration occurs; the filtered water is then returned to the aquarium. Filtration systems are the most complexly engineered component of most home aquaria, and various designs are used.

Combined biological and mechanical filtration systems are now common; these are designed to remove potentially dangerous build up of nitrogenous wastes and phosphates dissolved in the water, as well as particulate matter. In addition, some freshwater tanks (and most saltwater tanks) use powerheads to increase water circulation. The common freshwater aquarium maintained by a home aquarist typically includes a filtration system, an artificial lighting system, air pumps, and a heater. Freshwater aquaria remain the most popular due to their lower cost and easier maintenance, but marine (saltwater) aquaria have gained cachet as dedicated enthusiasts prove it is possible to preserve these challenging environments.

The most successful aquaria, as judged by the long-term survivability of its inhabitants, carefully emulate the natural environments that their residents would occupy in the wild. Aquaria can vary in size from a small bowl large enough for a single small fish, to the huge public aquaria that can simulate entire marine ecosystems. From the outdoor ponds and glass jars of antiquity, modern aquaria have evolved into a wide range of specialized systems. In the United States, a large minority (40%) of aquarists maintain two or more tanks at any one time.

The hobby has the strongest following in Europe, Asia, and North America. There are currently estimated to be about 60 million aquarium hobbyists worldwide, and many more aquaria kept by them. Popularization was also assisted by the availability of air freight, which allowed a much wider variety of fish to be successfully imported from distant regions of origin that consequently attracted new hobbyists. With electricity great improvements were made in aquarium technology, allowing artificial lighting as well as the aeration, filtration, and heating of the water.

Aquaria became more widely popular as houses became almost universally electrified after World War I. (One feature of some 19th-century aquaria that would prove curious to hobbyists today was the use of a metal base panel so that the aquarium water could be heated by flame.) Germans rivaled the British in their interest, and by the turn of the century Hamburg became the European port of entry for many newly seen species. The framed-glass aquarium was a specialized version of the glazed Wardian case developed for British horticulturists in the 1830s to protect exotic plants on long sea voyages. The keeping of fish in an aquarium first became a popular hobby in Britain only after ornate aquaria in cast-iron frames were featured at the Great Exhibition of 1851.

The concept of keeping aquatic life in glass containers, then, dates to at latest this period. In the 18th century, the biologist Abraham Trembley kept hydra found in the garden canals of the Bentinck residence 'Sorgvliet' in the Netherlands, in large cylindrical glass vessels for study. In 1665 the diarist Samuel Pepys recorded seeing in London "a fine rarity, of fishes kept in a glass of water, that will live so forever, and finely marked they are, being foreign." The fish observed by Pepys were likely to have been the paradise fish, Macropodus opercularis, a familiar garden fish in Canton, China, where the East India Company was then trading. However, it is difficult to pinpoint the exact date of this development.

The concept of an aquarium, designed for the observation of fish in an enclosed, transparent tank to be kept indoors, emerged more recently. The Chinese brought goldfish indoors during the Song dynasty to enjoy them in large ceramic vessels. Many other cultures also have a history of keeping fish for both functional and decorative purposes. Depictions of the sacred fish of Oxyrhynchus kept in captivity in rectangular temple pools have been found in ancient Egyptian art.

In China, selective breeding of carp into today's popular koi and goldfish is believed to have begun over 2,000 years ago. Ancient Sumerians were known to keep wild-caught fish in ponds, before preparing them for meals. The keeping of fish in confined or artificial environments is a practice with deep roots in history. The word aquarium itself is taken directly from the latin aqua, meaning water, with the suffix -rium, meaning "place" or "building".

. Other components in maintaining a suitable aquarium environment include appropriate species selection, management of biological loading, and good physical design. The nitrogen cycle describes the flow of nitrogen from input via food, through toxic nitrogenous waste produced by tank inhabitants, to metabolism to less toxic compounds by beneficial bacteria populations. Controlling water quality includes managing the inflow and outflow of nutrients, most notably the management of waste produced by tank inhabitants.

The careful aquarist dedicates considerable effort to maintaining a tank ecology that mimics its inhabitants' natural habitat. Inhabitants for aquaria are often collected from the wild, although there is a growing list of organisms that are bred in captivity for supply to the aquarium trade. These characteristics, and others, determine the type of fish and other inhabitants that can survive and thrive in the aquarium. Aquaria are usually classified as containing fresh or salt water, at tropical or cold water temperatures.

A wide variety of aquaria are now kept by hobbyists, ranging from a simple bowl housing a single fish to complex simulated ecosystems with carefully engineered support systems. gallons) and a collection of about 580 species of aquatic life. Public aquaria reproduce the home aquarist's hobby on a grand scale — the Osaka Aquarium, for example, boasts a tank of 5,400 m³ (1.4 million U.S. From the 1850s, when the predecessor of the modern aquarium was first developed as a novel curiosity, the ranks of aquarists have swelled as more sophisticated systems including lighting and filtration systems were developed to keep aquarium fish healthy.

Aquarium keeping is a popular hobby around the world, with about 60 million enthusiasts worldwide. An aquarium (plural aquariums or aquaria) is a vivarium, usually contained in a clear-sided container (typically constructed of glass or high-strength plastic) in which water-dwelling plants and animals (usually fish, and sometimes invertebrates, as well as amphibians, marine mammals, and reptiles) are kept in captivity, often for public display; or it is an establishment featuring such displays.

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