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Aquarium

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   A tropical display tank at the Georgia Aquarium
   Enlarge
   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 novelty, 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,
   whilst the planned National institute for research into aquatic
   habitats in England would be at 40-hectares the world's largest
   aquarium.

   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 water or salt water and brackish 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. Failing to provide these conditions may invite
   Fish diseases.
   The main tank at Osaka Aquarium houses a whale shark
   Enlarge
   The main tank at Osaka Aquarium houses a whale shark

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.
   Enlarge
   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 Guangzhou (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

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

   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.
   Enlarge
   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, not only
   work in Marine aqauriums but also work in nutrient rich environments,
   but are made popular through the use of the Berlin System.

   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 behaviour 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
   Enlarge
   A saltwater aquarium

   The solute content of water is perhaps the most important aspect of
   water conditions, as total dissolved solids 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 PPT), simulating a lake or
   river environment; brackish water (a salt level of 0.5 to 30 PPT),
   simulating environments lying between fresh and salt, such as
   estuaries; and salt water or sea water (a salt level of 30 to 40 PPT),
   simulating an ocean or sea environment. Rarely, even higher salt
   concentrations are maintained in specialized tanks for raising brine
   organisms.

   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 the degree to which
   it is alkaline or acidic. Saltwater is typically alkaline, while the pH
   of fresh water varies more. Hardness measures overall dissolved mineral
   content; hard or soft 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 water supply network 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. There
   are two processes used for that: deionization or reverse osmosis. 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 a large volume 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 (77 °F), are much more common, and tropical
   fish are among the most popular aquarium denizens. 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

   A planted freshwater aquarium.
   Enlarge
   A planted freshwater aquarium.

   An aquarium can range from a small, unadorned glass bowl containing
   less than a litre of water – although generally unsuited for most fish
   - to immense 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, Italy, has recently taken the step of banning traditional
   goldfish bowls as inhumane. Practical limitations, most notably the
   weight (fresh water weighs about 8.3 pounds per U.S. gallon (1 kg/L),
   and salt water is even denser) 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 (19,000
   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 (see Expo '75) 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,
   aquatic 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 crustaceans, 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).

Ecology

   Ideal aquarium ecology reproduces the balance 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
   balance in the small ecosystem contained in his aquarium.

   Approximate balance 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 favour 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.
   Enlarge
   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 become
   bound in the biomass of plants. 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.

   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.

   New aquariums often have problems associated with the nitrogen cycle
   due to insufficient number of beneficial bacteria. Therefore new tanks
   have to be "matured" before stocking them with fish. There are two
   basic approaches to this: the fishless cycle and the silent cycle.

   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, allowing the necessary
   bacterial populations time to develope. 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.

   The largest bacterial populations in a tank are found in the filter.
   Therefore efficient filtration is vital. A vigorous cleaning of the
   filter is sometimes enough to seriously disturb the biological balance
   of an aquarium.

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

   19 Liter Aquarium, seems to be overcrowded
   Enlarge
   19 Liter Aquarium, seems to be overcrowded

   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 "7mm per liter of water" which dictates that the sum in cm
   of the lengths of all fish kept in an aquarium (excluding tail length)
   should not exceed the capacity of the tank measured in Liters (one inch
   of fish per U.S. gallon). 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. (Note that this rule of thumb
   breaks down for thick bodied fishes like some catfish, and aggressive
   fish like most Cichlids.) For goldfish and other high-waste fish, many
   aquarists recommend doubling the space allowance to one inch of fish
   per every two gallons and others even debate the usefulness of the
   "inch per gallon" rule because it fails to consider other important
   issues such as fish temperament, activity, compatibility with other
   tank mates(i.e. two male bettas shouldn't be kept together) dimensions
   of aquarium, and the filtration capabilities of the aquarium. The
   safest method of determining the stocking limits and compatibility is
   to talk to an experienced aquarist or group of aquarists at a local
   organization or a dedicated online forum.

   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
   Enlarge
   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 tanks 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,
   Philadelphia 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. The early
   (1911) Philadelphia Aquarium, built in the city's disused water works,
   ironically had to switch to treated city water when the nearby river
   became too contaminated. Similarly, 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.

   Retrieved from " http://en.wikipedia.org/wiki/Aquarium"
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