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.
. 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. China and France are also developing other satellite navigation systems. A moving walkway now transports visitors through, and groups of school children occasionally hold sleepovers there beneath the swimming sharks and rays. The European Union is developing Galileo as an alternative to GPS, planned to be in operation by 2010. The 110-meter tunnel was built from one-tonne slabs of German sheet plastic that were shaped locally in an oven. There are plans to restore GLONASS to full operation by 2008.

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. Russia operates an independent system called GLONASS (global navigation system), although with only twelve active satellites as of 2004, the system is of limited usefulness. 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. There were also incidents of unintentional jamming, traced back to malfunctioning TV antenna preamplifiers. An inland pioneer was Chicago's Shedd Aquarium that received seawater shipped by rail in special tank cars. According to the reference below, "IFR pilots should have a fallback plan in case of a GPS malfunction". Most public aquaria are located close to the ocean, for a steady supply of natural seawater. And there has been at least one well-documented case of unintentional jamming; if similar, but stronger, signals were generated on purpose, they could interfere with aviation GPS receivers at a range of 50 km.

Following early examples of Detroit, New York and San Francisco, many major cities now have public aquaria. A detailed description of how to build a GPS jammer was posted on a hackers' site by an anonymous author. Barnum quickly followed with the first American aquarium, opened on Broadway in New York. Air Force conducted GPS jamming exercises in 2003. P.T. The U.S. The first public aquarium opened in London's Regent's Park in 1853. In either case, the jammers are attractive targets for anti-radiation missiles.

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. Some officials believe that jammers could be used to attract the precision-guided munitions towards noncombatant infrastructure, other officials believe that the jammers are completely ineffective. Also as with zoos, aquaria usually have specialized research staff who study the habits and biology of their specimens. invasion of Afghanistan. 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. government believes that such jammers were used occasionally during the U.S. A good aquarium will have special exhibits to entice repeat visitors, in addition to its permanent collection. The U.S.

Operationally, a public aquarium is similar in many ways to a zoo or museum. GPS jammers are available, from Russia, and are about the size of a cigarette box. Aquatic and semiaquatic animals, including otters and penguins, may also be kept by public aquaria. A large part of modern munitions, the so-called "smart bombs" or precision-guided munitions, use GPS. gallons of water and can house large species, including dolphins, sharks or beluga whales. The increased accuracy comes mostly from being able to use both the L1 and L2 frequencies and thus better compensate for the varying signal delay in the ionosphere (see above). The largest tanks hold millions of U.S. Military (and selected civilian) users still enjoy some technical advantages which can give quicker satellite lock and increased accuracy.

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. Authorized military units are still able to decrypt the corrected signals using a tamper-resistant hardware module called an SAASM, Selective Availability / Anti-Spoofing Module. Public aquaria are facilities open to the public for viewing of aquatic species in aquaria. The original SA system could only limit the accuracy of GPS signals world-wide, or not at all. 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. The US military maintains the ability to use a more advanced version of Selective Availability, called "Selective Deniability", to reduce the accuracy of civilian GPS units in a specific area without affecting the rest of the world. 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. [9].

The true maximum or ideal biological loading of a system is very difficult to calculate, even on a theoretical level. The military resisted for most of the 1990s, but SA was eventually turned off in 2000 following an announcement by then US President Bill Clinton, allowing all users to enjoy nearly the same level of access. For goldfish and other high-waste fish, some aquarists recommend doubling the space allowance to one inch of fish per every two gallons. This would save the FAA millions of dollars every year in maintenance of their own, less accurate, radio navigation systems. 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. In the 1990s the FAA started pressuring the military to turn off SA permanently. gallons (about 7 mm per liter of water). During the Gulf War, the shortage of military GPS units and the wide availability of civilian ones among personnel resulted in disabling the Selective Availability.

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. In order to improve the usefulness of GPS for civilian navigation, Differential GPS was used by many civilian GPS receivers to greatly improve accuracy. Perhaps the most popular of these is the "one inch of fish per U.S. The inaccuracy of the civilian signal was deliberately encoded so as not to change very quickly, for instance the entire eastern US area might read 30 m off, but 30 m off everywhere and in the same direction. In order to prevent biological overloading of the system, aquarists have developed a number of rules of thumb. SA typically added signal errors of up to about 10 m horizontally and 30 m vertically. Physically, only a limited size and number of plants and animals can be fit into an aquarium while still providing room for movement. Additional accuracy was available in the signal, but in an encrypted form that was only available to the United States military, its allies and a few others, mostly government users.

The capacity of nitrifying bacteria is limited by the physical space they have available to colonize. When it was first deployed, GPS included a feature called Selective Availability (or SA) that introduced intentional errors of up to a hundred meters into the publicly available navigation signals, making it difficult to use for guiding long range missiles to precise targets. The surface area of water exposed to air limits dissolved oxygen intake by the tank. The accuracy of GPS can be improved in a number of ways:. In addition, there are several fundamental constraints on biological loading based on the size of an aquarium. The citation accompanying the presentation of the trophy honors the GPS Team "for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50 years ago.". High biological loading in an aquarium represents a more complicated tank ecology, which in turn means that equilibrium is easier to perturb. Air Force, the Aerospace Corporation, Rockwell International Corporation, and IBM Federal Systems Company.

Biological loading is a measure of the burden placed on the aquarium ecosystem by its living inhabitants. This team consists of researchers from the Naval Research Laboratory, the U.S. 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. Collier Trophy, the most prestigious aviation award in the United States. Sulfur, iron, and micronutrients also cycle through the system, entering as food and exiting as waste. On February 10, 1993, the National Aeronautic Association selected the Global Positioning System Team as winners of the 1992 Robert J. The phosphate cycle is an important, although often overlooked, nutrient cycle. Two GPS developers have received the National Academy of Engineering Charles Stark Draper prize year 2003:.

Carbon dioxide escapes the system into the air. Bartolomé Coll has recently developed the basic notions necessary for a fully relativistic theory of Positioning Systems [7]. Dissolved oxygen enters the system at the surface water-air interface or through the actions of an air pump. Whether relativity must be considered as a mere correction to a Newtonian GPS theory, or, rather, as the necessary foundation of a cleaner (and more fundamental) GPS theory, is currently under debate. Nitrogen is not the only nutrient that cycles through an aquarium. Neil Ashby presented a good account of how these relativistic corrections are applied, why, and their orders of magnitude, in Physics Today (May 2002) [6]. Improperly cycled aquaria can quickly accumulate toxic concentrations of nitrogen waste and kill its inhabitants. This offset is a practical demonstration of the theory of relativity in a real-world system; it is exactly that predicted by the theory, within the limits of accuracy of measurement.

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. This amounts to a discrepancy of around 38 microseconds per day, which is corrected by electronics on each satellite. 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. The clocks on the satellites are also affected by both special and general relativity, which causes them to run at a slightly faster rate than do clocks on the Earth's surface. During this process, ammonia, nitrite, and nitrate levels are tested to monitor progress. Several frequencies make up the GPS electromagnetic spectrum:. Instead, small amounts of ammonia are added to the tank to feed the bacteria being cultured. Shorter multipath signals from ground reflections can often be very close to the direct signals, and can greatly reduce precision.

As the name of the former implies, no fish are kept in a tank undergoing a fishless cycle. For shorter delay multipath signals that result from reflections from the ground, special antenna features may be used such as a ground plane, or a choke ring antenna. Other cycling methods that have gained popularity in recent years are the fishless cycle and the silent cycle. A variety of receiver techniques, most notably Narrow Correlator spacing, have been developed to mitigate multipath errors. 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). For long delay multipath signals, the receiver itself can filter the signals out. 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. GPS signals can also be affected by multipath reflections of the radio signals off the ground and/or surrounding structures (buildings, canyon walls, etc).

New aquaria also do not usually have the required populations of bacteria for the handling of nitrogen waste. Newer GPS receivers can compare the phase difference between the L1 and L2 frequencies to actually measure the atmospheric effects on the signals and apply precise corrections.[citation needed]. 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. Because ionospheric delay affects the speed of radio waves differently based on their frequencies, a second frequency band was added to help eliminate this type of error. Aquaria kept by hobbyists often do not have the requisite populations of bacteria needed to detoxify nitrogen waste from tank inhabitants. Once the receiver's rough location is known, an internal mathematical model can be used to estimate and correct for the error. A balanced system, in which the fish eat the plants, is generally difficult to create. The effect is minimized when the satellite is directly overhead and becomes greater toward the horizon, as the satellite signals must travel through the greater "thickness" of the ionosphere as the angle increases.

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. One of biggest problems for GPS accuracy is that changing atmospheric conditions change the speed of the GPS signals unpredictably as they pass through the ionosphere. 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). The receiver is able to determine exactly when the signals were received by adjusting its internal clock (and therefore the spheres' radii) so that the spheres intersect near one point. However, this is only temporary, as the plants release nitrogen back into the water when older leaves die off and decompose. Fortunately, even the relatively simple clock within the receiver provides an accurate comparison of the timing of the signals from the different satellites. When plants metabolize nitrogen compounds, they remove nitrogen from the water by using it to build biomass. One complication is that GPS receivers do not have atomic clocks, so the precise time is not known when the signals arrive.

In addition to bacteria, aquatic plants also eliminate nitrogen waste by metabolizing ammonia and nitrate. In practice, GPS calculations are more complex for several reasons. 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. Once the location and distance of each satellite is known, the receiver should theoretically be located at the intersection of four imaginary spheres, one around each satellite, with a radius equal to the time delay between the satellite and the receiver multiplied by the speed of the radio signals. (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. Each satellite uses a different sequence, which lets them share the same radio frequencies, using Code Division Multiple Access, while still allowing receivers to identify each satellite. Another type of bacteria, genus Nitrospira, converts nitrite into nitrate, a less toxic substance to aquarium inhabitants. In order to measure the delay, the satellite sends a repeating 1,023 bit long pseudo random sequence; the receiver knows the seed of the sequence, constructs an identical sequence and shifts it until the two sequences match.

Nitrite is also highly toxic to fish in high concentrations. The receiver calculates the orbit of each satellite based on information encoded in their radio signals, and measures the distance to each satellite, called a pseudorange, based on the time delay from when the satellite signals were sent until they were received. Nitrifying bacteria capture ammonia from the water and metabolize it to produce nitrite. GPS receivers calculate their current position (latitude, longitude, elevation), and the precise time, using the process of trilateration after measuring the distance to at least four satellites by comparing the satellites' coded time signal transmissions. The nitrogen waste produced in a tank is metabolized in aquaria by a type of bacteria known as nitrifiers (genus Nitrosomonas). Each satellite repeatedly broadcasts its own orbital elements, and a precise time-code. A well-balanced tank contains organisms that are able to metabolize the waste products of other aquarium residents. They regularly synchronize the atomic clocks onboard each satellite, and send updates to the satellites of their observed position in orbit.

Nitrogen waste products become toxic to fish and other aquarium inhabitants at high concentrations. Ground-based observatories around the world monitor the flight paths of the GPS satellites. Ammonia is also produced through the decomposition of plant and animal matter, including fecal matter and other detritus. [5]. 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. The orbits are designed so at least four satellites are always within line of sight from almost any place on earth. Of primary concern to the aquarist is management of the biological waste produced by an aquarium's inhabitants. Each satellite circles the Earth twice each day at an altitude of 20,200 kilometres (12,600 miles).

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. The GPS system is made up of a satellite constellation of 24 working satellites and three spares in intermediate circular orbits, in 6 orbital planes. gallon (400 L) tank with many other fish in it represents only a minor change in the balance of the tank. The oldest GPS satellite still in operation was launched in February 1989. gallon tank (11 L) causes dramatic changes in the system, while the death of that same fish in a 100 U.S. The most recent launch was in September 2005. For example, the death of the only fish in a three U.S. [4].

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. The first modern Block-II satellite was launched in February 1989, and a complete constellation of 24 satellites was in orbit by 1993. Approximate equilibrium is facilitated by large volumes of water. By 1985, ten more experimental Block-I satellites had been launched to validate the concept. Typically an aquarium keeper must take steps to maintain equilibrium in the small ecosystem contained in his aquarium. In 1983, after Soviet jet interceptors shot down the civilian airliner KAL 007 in restricted Soviet airspace, killing all 269 people on board, Ronald Reagan announced that the GPS system would be made available for civilian uses once it was completed. As an example, a balanced predator-prey relationship is nearly impossible to maintain in even the largest of aquaria. The GPS satellites were initially manufactured by Rockwell and now manufactured by Lockheed Martin.

In practice it is virtually impossible to maintain a perfect balance. The first experimental Block-I GPS satellite was launched in February 1978 [3]. Ideal aquarium ecology reproduces the equilibrium found in nature in the closed system of an aquarium. It was only a small leap of logic to realize that the converse was also true; if the satellite's position was known then they could identify their own position on Earth. 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. They realized that since they knew their exact location on the globe, they could pinpoint where the satellite was along its orbit by measuring the Doppler distortion. 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. They discovered that, due to the Doppler effect, the frequency of the signal being transmitted by Sputnik was higher as the satellite approached, and lower as it continued away from them.

Aquaculture is the cultivation of aquatic organisms in a controlled environment. Kershner were monitoring Sputnik's radio transmissions. Breeding programs for freshwater species are comparatively more advanced than for saltwater species. Richard B. Captive breeding programs of marine organisms for the aquarium trade have been urgently in development since the mid-1990s. scientists led by Dr. 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. A team of U.S.

Since the 'fighting fish' Betta splendens was first successfully bred in France in 1893, captive spawning techniques have been slowly discovered. The inspiration for the GPS system came when the Soviets launched the first Sputnik in 1957. 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. However, this is usually corrected on the display within 15 minutes once the UTC offset message is received for the first time. 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. New GPS units will initially show the incorrect time after achieving a GPS lock for the first time. Additionally, the destructive fishing techniques used have become a growing concern to environmentalists and hobbyists alike. Receivers thus apply a clock-correction offset (which is periodically transmitted along with the other data) in order to display UTC correctly, and optionally adjust for a local time zone.

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. Today, GPS time is 14 seconds ahead [2] of UTC, because it does not follow leap seconds. More recently, the potentially detrimental environmental impact of fish and plant collecting has come to the attention of aquarists worldwide. The atomic clocks on the satellites are set to "GPS time", which is the number of seconds since 00:00:00 UTC, January 6, 1980. 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. For instance, when deploying sensors (for seismology or other monitoring application), GPS may be used to provide each recording apparatus with some precise time source, so that the time of events may be recorded accurately. Many others are weakened by stress and become diseased upon arrival. Many synchronization systems use GPS as a source of accurate time, hence one of the most common applications of this use is that of GPS as a reference clock for time code generators or NTP clocks.

The shipping process is very hazardous for the fish involved; mortality rates are high. This allows the data to be reported in real-time, using either web browser based tools or customized software. Collecting expeditions can be lengthy and costly, and are not always successful. The recorded data can be stored within the tracking unit, or it may be transmitted to a central location, or internet-connected computer, using a cellular modem, 2-way radio, or satellite. The practice of collection in the wild for eventual display in aquaria has several disadvantages. A GPS tracking system uses GPS to determine the location of a vehicle, person, or pet and to record the position at regular intervals in order to create a track file or log of activities. 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. On the other extreme, some airlines integrate GPS tracking of the aircraft into their aircraft's seat-back television entertainment systems, available even during takeoff and landing to all passengers.

In many places of the world, impoverished local villagers collect specimens for the aquarium trade as their prime means of income. Additionally, some airline companies disallow use of hand-held receivers for security reasons, such as unwillingness to let ordinary passengers track the flight route. Collection of fish, plants, and invertebrates from the wild for supply to the aquarium trade continues today at locations around the world. Most airlines allow private use of ordinary GPS units on their flights, except during landing and take-off, like all other electronic devices. 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. Geocaching often includes walking or hiking to natural locations, and is popular with both children and adults. Fish and plants for the first modern aquaria were gathered from the wild and transported (usually by ship) to European and American ports. Geocaching involves using a hand-held GPS unit to travel to a specific longitude and lattitude to search for objects deliberately hidden there by other Geocachers.

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). The availability of hand-held GPS receivers for a cost of about $90 and up (as of March 2005) has led to recreational applications including Geocaching. 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. For information about navigation systems for the visually impaired, including MoBIC, Drishti, Brunel Navigation System for the Blind, NOPPA, BrailleNote GPS, and Trekker, refer to the main article GPS for the visually impaired. These aquaria focus on the rich diversity of invertebrate life in these environments, and typically include only a limited number of small fish. More costly and precise receivers are used by land surveyors to locate boundaries, structures, and survey markers, and for road construction. These aquaria attempt to simulate the complex reef ecosystems found in warm, tropical oceans around the world. Low cost GPS receivers are often combined in a bundle with a PDA, car computer, or vehicle tracking system.

In addition to the types above, a special category of saltwater aquaria is the reef aquarium. Glider pilots use the logged signal to verify their arrival at turnpoints in competitions. 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. Hand-held GPS receivers can be used by mountain climbers and hikers. These ecotype aquaria might be considered the most sophisticated hobby aquaria; indeed, reputable public aquaria all use this approach in their exhibits whenever possible. The system can also be used by computer controlled harvesters, mine trucks and other vehicles. 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. GPS is used by people around the world as a navigation aid in cars, airplanes, and ships.

Such tanks are common in fishrooms, where people keep many tanks at home. Commercial civilian GPS receivers are required to have limits on the velocities and altitudes at which they will report coordinates; this is to prevent them from being used to create improvised missiles. Some tanks of this sort are used simply to house adults for breeding. The satellites also carry nuclear detonation detectors, which form a major portion of the United States Nuclear Detonation Detection System. They can be simple as bare bottom with a few necessities or a complex planted aquarium. GPS allows accurate targeting of cruise missiles and precision-guided munitions (or "smart bombs"), as well as improved command and control of forces through improved locational awareness. These tanks are often used for killifish, livebearers, cichlids etc. .

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. Although the cost of maintaining the system is approximately US$400 million per year, including the replacement of aging satellites, GPS is available for free use in civilian applications as a public good. 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. The satellite constellation is managed daily by the 2d Space Operations Squadron at Schriever Air Force Base. 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. United States Department of Defense developed the system, officially named NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System). Aggressive tanks, in contrast, house a limited number of species that can be aggressive toward other fish, or are able to withstand aggression well. GPS accuracy can be improved further, to about 1 cm (half an inch) over short distances, using techniques such as Differential GPS (DGPS).

This is the most common type of hobby aquarium kept today. The Wide-Area Augmentation System (WAAS), available since August 2000, increases the accuracy of GPS signals to within 2 meters (6 ft) [1] for compatible receivers. Community tanks house several species that are not aggressive toward each other. GPS also provides an extremely precise time reference, required for some scientific research, including the study of earthquakes. Perhaps the most popular of these is the division of aquaria into either a community or aggressive tank type. Since GPS was declared fully operational in 1993, it has become a vital global utility, indispensible for modern navigation on land, sea, and air around the world, as well as an important tool for map-making, and land surveying. Several theories on species selection circulate within the community of hobby aquarists. A constellation of more than two dozen GPS satellites broadcasts precise timing signals by radio to electronic GPS receivers which allow them to accurately determine their location (longitude, latitude, and altitude) in real time, day or night, in any weather.

The size of public aquaria are usually limited by cost considerations. The Global Positioning System, usually called GPS, is the Earth's only fully-functional satellite navigation system. 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. GPS Anti-Jamming Protection. The Okinawa Churaumi Aquarium is the world's second largest aquarium and part of the Ocean Expo Park located in Motobu, Okinawa. The hunt for an unintentional GPS jammer. 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. GPS jamming.

The Monterey Bay Aquarium has an acrylic viewing window into their largest tank. noaa.gov Selective Availability Factsheet (pdf) or [10]. gallons (1,500 m³). This is similar in principle to the combination of GPS and inertial navigation used in ships and aircraft, but less accurate and less expensive because it only fills in for short periods. gallons (7,500 m³), as well as two others of 400,000 U.S. Many automobile GPS systems combine the GPS unit with a gyroscope and speedometer pickup, allowing the computer to maintain a continuous navigation solution by dead reckoning when buildings, terrain, or tunnels block the satellite signals. The Shedd Aquarium features an individual aquarium of two million U.S. This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time (real-time kinematic positioning, RTK).

Public aquaria designed for exhibition of large species or environments can be dramatically larger than any home aquarium. This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. gallons (several cubic meters), at great effort and expense. In this approach, accurate determination of range signal can be resolved to an accuracy of less than 10 centimetres. However, some dedicated aquarists have been known to construct custom aquaria of up to several thousand U.S. Relative Kinematic Positioning (RKP) is another approach for a precise GPS-based positioning system. gallons). Wide Area GPS Enhancement (WAGE) is an attempt to improve GPS accuracy by providing more accurate satellite clock and ephemeris (orbital) data to specially-equipped receivers.

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. CPGPS working to within 1% of perfect transition matching can achieve 3 mm ambiguity; in reality, CPGPS coupled with DGPS normally realizes 20-30 cm accuracy. Practical limitations, most notably the weight (water weighs about 8.3 pounds per U.S. The phase difference error in the normal GPS amounts to a 2-3 m ambiguity. 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. CPGPS solves this problem by using the L1 carrier, which has a period 1/1000 that of the C/A bit width, to define the transition point instead. gallons (11 L). A successful correlation could be defined in a number of various places along the rising/falling edge of the pulse, which imparts timing errors.

Aquaria kept in homes by hobbyists can be as small as 3 U.S. The problem arises from the fact that the transition from 0-1 or 1-0 on the C/A signal is not instantaneous, it takes a non-zero amount of time, and thus the correlation (satellite-receiver sequence matching) operation is imperfect. 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. This technique utilizes the 1.575 GHz L1 carrier wave to act as a sort of clock signal, resolving ambiguity caused by variations in the location of the pulse transition (logic 1-0 or 0-1) of the C/A PRN signal. 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. A Carrier-Phase Enhancement (CPGPS). 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). Exploitation of DGPS for Guidance Enhancement (EDGE) is an effort to integrate DGPS into precision guided munitions such as the Joint Direct Attack Munition (JDAM).

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. These correction data are typically useful for only about a thirty to fifty kilometer radius around the transmitter. Water movement can also be important in accurately simulating a natural ecosystem. But in this case, the correction data are transmitted from a local source, typically at an airport or another location where accurate positioning is needed. Cold water aquaria are those with temperatures below what would be considered tropical; a variety of fish are better suited to this cooler environment. This is similar to WAAS, in that similar correction data are used. 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. A Local Area Augmentation System (LAAS).

cold water. However, variants of the WAAS system are being developed in Europe (EGNOS, the Euro Geostationary Navigation Overlay Service), and Japan (MSAS, the Multi-Functional Satellite Augmentation System), which are virtually identical to WAAS. The temperature of the water forms the basis of one of the two most basic aquarium classifications: tropical vs. The current WAAS system only works for North America (where the reference stations are located), and due to the satellite location the system is only generally usable in the eastern and western coastal regions. Secondary water characteristics are also important to the success of an aquarium. Although only a few WAAS satellites are currently available as of 2004, it is hoped that eventually WAAS will provide sufficient reliability and accuracy that it can be used for critical applications such as GPS-based instrument approaches in aviation (landing an airplane in conditions of little or no visibility). 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. This uses a series of ground reference stations to calculate GPS correction messages, which are uploaded to a series of additional satellites in geosynchronous orbit for transmission to GPS receivers, including information on ionospheric delays, individual satellite clock drift, and suchlike.

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. The Wide Area Augmentation System (WAAS). Brackish or saltwater aquaria require the addition of a mixture of salts and other minerals, which are commercially available for this purpose. The "difference" is broadcast as a local FM signal, allowing many civilian GPS receivers to "fix" the signal for greatly improved accuracy. 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. Differential GPS (DGPS) can improve the normal GPS accuracy of 4-20 meters to 1-3 meters.[8] DGPS uses a network of stationary GPS receivers to calculate the difference between their actual known position and the position as calculated by their received GPS signal. Home aquarists typically use modified tap water supplied through their local municipal water system to fill their tanks. Bradford Parkinson, teacher of aeronautics and astronautics at Stanford University developed the system.

Dissolved organic content and dissolved gases content are also important factors. Ivan Getting, emeritus president of The Aerospace Corporation and engineer at the Massachusetts Institute of Technology established the basis for GPS, improving on the World War II land-based radio system called LORAN (Long-range Radio Aid to Navigation). Hardness measures overall dissolved mineral content; soft or hard water may be preferred. The first Block IIF satellite that would provide this signal is set to be launched in 2007. The pH of the water is a measure of alkalinity or acidity. This frequency falls into an internationally protected range for aeronautical navigation, promising little or no interference under all circumstances. Several other water characteristics result from dissolved contents of the water, and are important to the proper simulation of natural environments. L5 (1176.45 MHz):
Proposed for use as a civilian safety-of-life signal.

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. L4 (1841.40 MHz):
Being studied for additional ionospheric correction. Salt content, or salinity, is the most basic classification of water conditions. L3 (1381.05 MHz):
Carries the signal for the GPS constellation's alternative role of detecting missile/rocket launches (supplementing Defense Support Program satellites), nuclear detonations, and other high-energy infrared events. 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. Recognizing the civilian need for increased accuracy, "modernized" IIR-M (IIR-14 (M) and later) satellites carry a civilian signal interleaved with an improved military signal on both the L1 and L2 frequencies. The size of an aquarium also limits the aquarist in what types of ecosystems he can reproduce, species selection, and biological loading. In spite of not having the P(Y) code encryption key, several high-end GPS receiver manufacturers have developed techniques for utilizing this signal (in a round-about manner) to increase accuracy and remove error caused by the ionosphere.

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 keys are changed on a daily basis. Aquaria can be classified by several variables that determine the type of aquatic life that can be suitably housed. government and are generally provided only for military use. The combined function of these elements is to maintain appropriate water quality and characteristics suitable for the aquarium's residents. The encryption keys required to directly use the P(Y) code are tightly controlled by the U.S. 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. L2 (1227.60 MHz):
Usually carries only the P(Y) code.

An aquarium's physical characteristics form another aspect of aquarium design. L1 (1575.42 MHz):
Carries a publicly usable coarse-acquisition (C/A) code as well as an encrypted precision P(Y) code. 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. Precise time reference. 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. GPS tracking. 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. GPS on airplanes.

Air pumps are employed to adequately oxygenate (or in the case of a heavily planted aquarium, provide carbon dioxide to) the water. Geocaching. Protein skimmers, filtration devices that remove proteins and other waste from the water, are usually found only in salt water aquaria. GPS for the visually impaired. 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. Surveying. Filtration systems are the most complexly engineered component of most home aquaria, and various designs are used. Navigation.

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. Military Applications. 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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