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. More recently, in the 1960s, dessert fondue recipes have appeared, typically a caquelon of melted chocolate into which pieces of fruit or pastries are dipped. 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. (Some fondue restaurant chains also provide flavored batters to coat the food with before frying, but it is not traditional.). A moving walkway now transports visitors through, and groups of school children occasionally hold sleepovers there beneath the swimming sharks and rays. An assortment of sauces are provided for dipping. The 110-meter tunnel was built from one-tonne slabs of German sheet plastic that were shaped locally in an oven. In Fondue Bourguignonne, small cubes of meat (normally horse meat or beef) and sometimes vegetables or seafood are skewered on the fondue fork and fried by each person at the table.

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. Fondue Chinoise is named after its relation to the Asian hot pot. 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. As with fondue Bourguignonne, dipping sauces are served. An inland pioneer was Chicago's Shedd Aquarium that received seawater shipped by rail in special tank cars. In this variety of fondue, the diner dips rolled shaved beef into a simmering broth. Most public aquaria are located close to the ocean, for a steady supply of natural seawater. Individual portions that can be cooked using a microwave oven are also available.

Following early examples of Detroit, New York and San Francisco, many major cities now have public aquaria. Modern instant fondues are surprisingly accurate renditions of the homemade product, requiring little more than to be melted in the caquelon just before serving. Barnum quickly followed with the first American aquarium, opened on Broadway in New York. In 1955, the first instant fondue was brought on the market. P.T. Fondue was a perfect solution, permitting a diner to consume a half-pound of cheese in one sitting. The first public aquarium opened in London's Regent's Park in 1853. While cheese fondue is a traditionally Swiss dish, it was not common until the 1950s, when the slowing cheese industry in Switzerland needed a way to increase sales.

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. In French, this is commonly referred to as 'la religieuse' ("the nun"). Also as with zoos, aquaria usually have specialized research staff who study the habits and biology of their specimens. Ideally, when the fondue is finished, there will be a thin crust of toasted (but not burnt) cheese in the bottom of the caquelon. 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. In a perfect cheese fondue, the mixture is held at a temperature low enough to prevent burning, but hot enough to keep the fondue smooth and liquid. A good aquarium will have special exhibits to entice repeat visitors, in addition to its permanent collection. Well-known variations include:.

Operationally, a public aquarium is similar in many ways to a zoo or museum. The most common recipe requires 1 dl of dry white wine per person, and 200 g of a mix of hard (such as Gruyère) and semi-hard (such as Emmental, Vacherin or raclette) cheeses. Aquatic and semiaquatic animals, including otters and penguins, may also be kept by public aquaria. Cubed crusty bread is dipped using a fondue fork. gallons of water and can house large species, including dolphins, sharks or beluga whales. A small amount of corn starch or flour is added to prevent separation, often diluted in kirsch. The largest tanks hold millions of U.S. They are all cooked in a caquelon rubbed with a cut garlic clove.

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. Many varieties of cheese fondue exist, each with a unique name and different blend of cheeses, wine and seasoning, depending on where it is made. Public aquaria are facilities open to the public for viewing of aquatic species in aquaria. In some cheese fondues, potatoes or fruit are served instead of bread. 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. Local wines and seasonings were added and even the dry and hard bread tasted delicious after it was swirled in the creamy melted cheese. To do so, the variables for waste production rate, nitrification efficiency, gas exchange rate at the water surface, and many others would need to be determined. The Swiss found that melting stale cheese made it edible.

The true maximum or ideal biological loading of a system is very difficult to calculate, even on a theoretical level. During winter, fresh food became scarce. For goldfish and other high-waste fish, some aquarists recommend doubling the space allowance to one inch of fish per every two gallons. In the remote and isolated mountain villages in the Swiss Alps people had to rely upon locally made food. 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. Cheese fondue was invented out of necessity. gallons (about 7 mm per liter of water). .

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. If the bread or fruit is lost in the cheese, it is tradition for that person to buy a round of drinks or to be punished in another way. Perhaps the most popular of these is the "one inch of fish per U.S. Some people consider it rude to allow one's lips or tongue to touch the fondue fork, and with meat fondues one should use a dinner fork to remove the meat from the dipping utensil. In order to prevent biological overloading of the system, aquarists have developed a number of rules of thumb. As with other communal dishes, fondue has etiquette standards ranging from practical to amusing. Physically, only a limited size and number of plants and animals can be fit into an aquarium while still providing room for movement. Though cheese fondues are perhaps the best known kind, there are several other possibilities for the contents of the pot and what is used for dipping—recipes are not entirely fixed and vary depending on the cook.

The capacity of nitrifying bacteria is limited by the physical space they have available to colonize. The term "fondue" comes from the French "fondre" ("to melt"), referring to the fact that the contents of the pot are kept in a liquid state so that diners can use forks to dip into the sauce. The surface area of water exposed to air limits dissolved oxygen intake by the tank. Fondue refers to several French Swiss communal dishes shared at the table in an earthenware pot ("caquelon") over a small burner ("réchaud"). In addition, there are several fundamental constraints on biological loading based on the size of an aquarium. Fonduta: is prepared in the French-minority region of Aosta valley in Italy, and employs fontina, milk, eggs, and truffles. High biological loading in an aquarium represents a more complicated tank ecology, which in turn means that equilibrium is easier to perturb. Italian Fondues:

    .

    Biological loading is a measure of the burden placed on the aquarium ecosystem by its living inhabitants. Fondue Jurassienne: pure mature and normal comté. 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. Fondue Savoyarde: comté savoyard, beaufort, and emmental. Sulfur, iron, and micronutrients also cycle through the system, entering as food and exiting as waste. French Fondues:

      . The phosphate cycle is an important, although often overlooked, nutrient cycle. Mushroom Fondue : gruyère, Fribourg vacherin and mushrooms.

      Carbon dioxide escapes the system into the air. Spicy Fondue: gruyère, red and green peppers and chilli. Dissolved oxygen enters the system at the surface water-air interface or through the actions of an air pump. Tomato Fondue: Gruyère, Emmental and crushed tomatoes in the place of wine. Nitrogen is not the only nutrient that cycles through an aquarium. Fondue de Suisse centrale : gruyère, emmental and sbrinz. Improperly cycled aquaria can quickly accumulate toxic concentrations of nitrogen waste and kill its inhabitants. Fondue Fribourgeoise: pure Fribourg vacherin (often served with potatoes instead of bread).

      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. Fondue Vaudoise : gruyère. 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. Fondue Moitié-Moitié: (half-half): gruyère and Fribourg vacherin. During this process, ammonia, nitrite, and nitrate levels are tested to monitor progress. Fondue Neuchâteloise: gruyère and emmental. Instead, small amounts of ammonia are added to the tank to feed the bacteria being cultured. Swiss Fondues:

        .

        As the name of the former implies, no fish are kept in a tank undergoing a fishless cycle. Other cycling methods that have gained popularity in recent years are the fishless cycle and the silent cycle. 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). 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.

        New aquaria also do not usually have the required populations of bacteria for the handling of nitrogen waste. 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. Aquaria kept by hobbyists often do not have the requisite populations of bacteria needed to detoxify nitrogen waste from tank inhabitants. A balanced system, in which the fish eat the plants, is generally difficult to create.

        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. 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). However, this is only temporary, as the plants release nitrogen back into the water when older leaves die off and decompose. When plants metabolize nitrogen compounds, they remove nitrogen from the water by using it to build biomass.

        In addition to bacteria, aquatic plants also eliminate nitrogen waste by metabolizing ammonia and nitrate. 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. (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. Another type of bacteria, genus Nitrospira, converts nitrite into nitrate, a less toxic substance to aquarium inhabitants.

        Nitrite is also highly toxic to fish in high concentrations. Nitrifying bacteria capture ammonia from the water and metabolize it to produce nitrite. The nitrogen waste produced in a tank is metabolized in aquaria by a type of bacteria known as nitrifiers (genus Nitrosomonas). A well-balanced tank contains organisms that are able to metabolize the waste products of other aquarium residents.

        Nitrogen waste products become toxic to fish and other aquarium inhabitants at high concentrations. Ammonia is also produced through the decomposition of plant and animal matter, including fecal matter and other detritus. 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. Of primary concern to the aquarist is management of the biological waste produced by an aquarium's inhabitants.

        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. gallon (400 L) tank with many other fish in it represents only a minor change in the balance of the tank. gallon tank (11 L) causes dramatic changes in the system, while the death of that same fish in a 100 U.S. For example, the death of the only fish in a three U.S.

        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. Approximate equilibrium is facilitated by large volumes of water. Typically an aquarium keeper must take steps to maintain equilibrium in the small ecosystem contained in his aquarium. As an example, a balanced predator-prey relationship is nearly impossible to maintain in even the largest of aquaria.

        In practice it is virtually impossible to maintain a perfect balance. Ideal aquarium ecology reproduces the equilibrium found in nature in the closed system of an aquarium. 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. 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 is the cultivation of aquatic organisms in a controlled environment. Breeding programs for freshwater species are comparatively more advanced than for saltwater species. Captive breeding programs of marine organisms for the aquarium trade have been urgently in development since the mid-1990s. 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.

        Since the 'fighting fish' Betta splendens was first successfully bred in France in 1893, captive spawning techniques have been slowly discovered. 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. 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. Additionally, the destructive fishing techniques used have become a growing concern to environmentalists and hobbyists alike.

        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. More recently, the potentially detrimental environmental impact of fish and plant collecting has come to the attention of aquarists worldwide. 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. Many others are weakened by stress and become diseased upon arrival.

        The shipping process is very hazardous for the fish involved; mortality rates are high. Collecting expeditions can be lengthy and costly, and are not always successful. The practice of collection in the wild for eventual display in aquaria has several disadvantages. 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.

        In many places of the world, impoverished local villagers collect specimens for the aquarium trade as their prime means of income. Collection of fish, plants, and invertebrates from the wild for supply to the aquarium trade continues today at locations around the world. 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. Fish and plants for the first modern aquaria were gathered from the wild and transported (usually by ship) to European and American ports.

        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). 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. These aquaria focus on the rich diversity of invertebrate life in these environments, and typically include only a limited number of small fish. These aquaria attempt to simulate the complex reef ecosystems found in warm, tropical oceans around the world.

        In addition to the types above, a special category of saltwater aquaria is the reef aquarium. 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. These ecotype aquaria might be considered the most sophisticated hobby aquaria; indeed, reputable public aquaria all use this approach in their exhibits whenever possible. 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.

        Such tanks are common in fishrooms, where people keep many tanks at home. Some tanks of this sort are used simply to house adults for breeding. They can be simple as bare bottom with a few necessities or a complex planted aquarium. 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. 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. 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. Aggressive tanks, in contrast, house a limited number of species that can be aggressive toward other fish, or are able to withstand aggression well.

        This is the most common type of hobby aquarium kept today. Community tanks house several species that are not aggressive toward each other. Perhaps the most popular of these is the division of aquaria into either a community or aggressive tank type. Several theories on species selection circulate within the community of hobby aquarists.

        The size of public aquaria are usually limited by cost considerations. 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 Okinawa Churaumi Aquarium is the world's second largest aquarium and part of the Ocean Expo Park located in Motobu, Okinawa. 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 Monterey Bay Aquarium has an acrylic viewing window into their largest tank. gallons (1,500 m³). gallons (7,500 m³), as well as two others of 400,000 U.S. The Shedd Aquarium features an individual aquarium of two million U.S.

        Public aquaria designed for exhibition of large species or environments can be dramatically larger than any home aquarium. gallons (several cubic meters), at great effort and expense. However, some dedicated aquarists have been known to construct custom aquaria of up to several thousand U.S. gallons).

        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. Practical limitations, most notably the weight (water weighs about 8.3 pounds per U.S. 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. gallons (11 L).

        Aquaria kept in homes by hobbyists can be as small as 3 U.S. 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. 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. 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).

        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 movement can also be important in accurately simulating a natural ecosystem. Cold water aquaria are those with temperatures below what would be considered tropical; a variety of fish are better suited to this cooler environment. 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. The temperature of the water forms the basis of one of the two most basic aquarium classifications: tropical vs. Secondary water characteristics are also important to the success of an aquarium. 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.

        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. Brackish or saltwater aquaria require the addition of a mixture of salts and other minerals, which are commercially available for this purpose. 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. Home aquarists typically use modified tap water supplied through their local municipal water system to fill their tanks.

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

        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. Salt content, or salinity, is the most basic classification of water conditions. 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. The size of an aquarium also limits the aquarist in what types of ecosystems he can reproduce, species selection, and biological loading.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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