An aquarium (plural: aquariums or aquaria) is a vivarium of any size
having at least one transparent side in which aquatic plants or
animals are kept and displayed. Fishkeepers use aquaria to keep fish,
invertebrates, amphibians, aquatic reptiles such as turtles, and
aquatic plants. The term "aquarium", coined by English naturalist
Philip Henry Gosse, combines the
Latin root aqua, meaning water, with
the suffix -arium, meaning "a place for relating to". The aquarium
principle was fully developed in 1850 by the chemist Robert Warington,
who explained that plants added to water in a container would give off
enough oxygen to support animals, so long as the numbers of animals
did not grow too large. The aquarium craze was launched in early
Victorian England by Gosse, who created and stocked the first public
aquarium at the
London Zoo in 1853, and published the first manual,
The Aquarium: An Unveiling of the Wonders of the Deep Sea in 1854.
An aquarium is a water-filled tank in which fish swim about. Small
aquariums are kept in the home by hobbyists. There are larger public
aquariums in many cities. This kind of aquarium is a building with
fish and other aquatic animals in large tanks. A large aquarium may
have otters, turtles, dolphins, and other sea animals. Most aquarium
tanks also have plants.
An aquarist owns fish or maintains an aquarium, typically constructed
of glass or high-strength acrylic.
Cuboid aquaria are also known as
fish tanks or simply tanks, while bowl-shaped aquaria are also known
as fish bowls. Size can range from a small glass bowl, under a gallon
in volume, to immense public aquaria of several thousand gallons.
Specialized equipment maintains appropriate water quality and other
characteristics suitable for the aquarium's residents.
1 History and popularization
1.2 Nineteenth century
1.3 Twentieth century
Aquarium size and volume
2.3.1 Nano aquariums
4.1 Water conditions
4.2.1 The process
4.2.2 Maintaining the nitrogen cycle
4.3 Biological load
4.3.1 Calculating capacity
4.3.2 Other factors affecting capacity
6 Public aquaria
7 Virtual aquariums
8 See also
10 External links
History and popularization
In the Roman Empire, the first fish to be brought indoors was the sea
barbel, which was kept under guest beds in small tanks made of
marble. Introduction of glass panes around the year
50 AD allowed Romans to replace one wall of marble tanks, improving
their view of the fish. In 1369, the
Hongwu Emperor of China
established a porcelain company that produced large porcelain tubs for
maintaining goldfish; over time, people produced tubs that approached
the shape of modern fish bowls. Leonhard Baldner, who wrote Vogel-,
Fisch- und Tierbuch (Bird, Fish, and Animal Book) in 1666, maintained
weather loaches and newts.
An aquarium of the 1850s containing
Vallisneria spiralis and coldwater
fish from Shirley Hibberd's The Book of the
Aquarium and Water
Goldfish in a glass: portrait of Therese Krones, 1824
In 1832, Jeanne Villepreux-Power, a pioneering French marine
biologist, became the first person to create aquaria for experimenting
with aquatic organisms. In 1836, soon after his invention of the
Wardian case, Dr.
Nathaniel Bagshaw Ward
Nathaniel Bagshaw Ward proposed to use his tanks for
tropical animals. In 1841 he did so, though only with aquatic plants
and toy fish. However, he soon housed real animals. In 1838, Félix
Dujardin noted owning a saltwater aquarium, though he did not use the
term. In 1846,
Anne Thynne maintained stony corals and seaweed for
almost three years, and was credited as the creator of the first
balanced marine aquarium in London. English chemist Robert
Warington experimented with a 13-gallon container, which contained
goldfish, eelgrass, and snails, creating one of the first stable
aquaria. The aquarium principle was fully developed by Warington,
explaining that plants added to water in a container would give off
enough oxygen to support animals, so long as their numbers do not grow
too large. He published his findings in 1850 in the Chemical
The Jardin zoologique at the
Bois de Boulogne
Bois de Boulogne included an aquarium
that housed both fresh and saltwater animals, 1860 in Paris.
The keeping of fish in an aquarium became a popular hobby and spread
quickly. In the United Kingdom, it became popular after ornate aquaria
in cast-iron frames were featured at the Great Exhibition of 1851. In
1853, the aquarium craze was launched in England by Philip Henry Gosse
who created and stocked the first public aquarium in the London Zoo
which came to be known as the
Fish House. Gosse coined the word
"aquarium", opting for this term (instead of "aquatic vivarium" or
"aqua-vivarium") in 1854 in his book The Aquarium: An Unveiling of the
Wonders of the Deep Sea. In this book, Gosse primarily discussed
saltwater aquaria. In the 1850s, the aquarium became a fad in the
United Kingdom. Tank designs and techniques for maintaining water
quality were developed by Warington, later cooperating with Gosse
until his critical review of the tank water composition. Edward
Edwards developed these glass-fronted aquaria in his 1858 patent for a
"dark-water-chamber slope-back tank", with water slowly circulating to
a reservoir beneath.
Aquarium Should Be" – a humorous 1876 British engraving,
Thomas Huxley dreaming about sea creatures
Germans soon rivaled the British in their interest. In 1854, an
anonymous author had two articles published about the saltwater
aquaria of the United Kingdom: Die Gartenlaube (The Garden House)
entitled Der Ocean auf dem Tische (The Ocean on the Table). However,
in 1856, Der See im Glase (The Lake in a Glass) was published,
discussing freshwater aquaria, which were much easier to maintain in
landlocked areas. In 1862 William Alford Lloyd, then bankrupt
because of the craze in England being over, moved to Grindel Dammthor,
Hamburg, to supervise the installation of the circulating system and
tanks at the Hamburg Aquarium. During the 1870s, some
of the first aquarist societies were appearing in Germany. The
United States soon followed. Published in 1858, Henry D. Butler's The
Aquarium was one of the first books written in the United
States solely about the aquarium. According to the July issue of
The North American Review of the same year, William Stimson may have
owned some of the first functional aquaria, and had as many as seven
or eight. The first aquarist society in the United States was
New York City
New York City in 1893, followed by others. The New York
Aquarium Journal, first published in October 1876, is considered to be
the world's first aquarium magazine.
An antique cast-iron aquarium made by J. W. Fiske & Company in the
New York City
New York City 
Victorian era in the United Kingdom, a common design for the
home aquarium was a glass front with the other sides made of wood
(made watertight with a pitch coating). The bottom would be made of
slate and heated from below. More advanced systems soon began to
be introduced, along with tanks of glass in metal frames. During
the latter half of the 19th century, a variety of aquarium designs
were explored, such as hanging the aquarium on a wall, mounting it as
part of a window, or even combining it with a birdcage.
Pike in an aquarium circa 1908, at the Belle Isle Aquarium, Belle Isle
Around 1908, the first mechanical aquarium air pump was invented,
powered by running water, instead of electricity. The introduction
of the air pump into the hobby is considered by several historians of
the hobby to be a pivotal moment in its development.
Aquaria became more widely popular as houses had an electricity supply
after World War I.
Electricity allowed artificial lighting, as well as
aeration, filtration, and heating of the water. Initially, amateur
aquarists kept native fish (with the exception of goldfish); the
availability of exotic species from overseas further increased the
popularity of the aquarium. Jugs made from a variety of materials
were used to import fish from overseas, with a bicycle foot pump for
Plastic shipping bags were introduced in the 1950s,
making it easier to ship fish. The eventual availability of air
freight allowed fish to be successfully imported from distant
regions. In the 1960s, metal frames made marine aquaria almost
impossible due to corrosion, but the development of tar and silicone
sealant allowed the first all-glass aquaria made by Martin Horowitz in
Los Angeles, CA. The frames remained, however, though purely for
An aquarium in the
Burj Al Arab
Burj Al Arab in Dubai
In the United States, as of 1996, aquarium keeping is the second-most
popular hobby after stamp collecting. In 1999, an estimated 9.6
million US households owned an aquarium. Figures from the 2005/2006
APPMA National Pet Owners Survey report that Americans own
approximately 139 million freshwater fish and 9.6 million saltwater
fish. Estimates of the numbers of fish kept in aquaria in
Germany suggest at least 36 million. The hobby has the strongest
following in Europe, Asia, and North America. In the United States,
40% of aquarists maintain two or more tanks.
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The mid 1980s brought forth major advancements in aquarium design. A
spirited young cyclist from Japan named
Takashi Amano created the
Aquarium style when he created a fish tank in the image of a
stone-filled river. The tank housed Cardinal Tetras and was planted
solely with Echinodorus tenellus. This aquarium was the first Iwagumi
style layout and the precursor to modern aquascaping. Amano continued
to shape the world of planted aquaria. Many of his inventions were
critical to the success of planted aquaria. After noticing that his
red jacket appeared dark underwater, he hypothesized that aquatic
plants mostly utilize the blue spectrum of light for photosynthesis,
unlike terrestrial plants. With help from Panasonic, he developed a
blue-spectrum aquarium light that still offered attractive color
rendition. After realizing that Echinodorus tenellus grew more quickly
when nutrient capsules were placed near the roots of the plant, he
developed a nutrient-filled growing medium for aquarium plants. He
once experimentally poured several liters of soda water into one of
his aquariums. After seeing the plants vigorously photosynthesizing
the next morning, he developed the first pressurized carbon dioxide
injection system for aquarium use. All of these inventions were a huge
contribution to planted aquaria. They made it easy to maintain
healthy, fast, natural-looking growth in aquarium plants as well as
making it possible to grow countless species of plant that were
impossible to grow with previous systems. However, he didn't solely
contribute to aquarium technology. He was also a major contributor to
aquarium design. A lover of nature and photography, Amano was
frustrated with aquarium design of the time. The dominant style was
the Dutch aquarium, in which bushes of stem plant clippings are placed
in rows, like an underwater flower garden. Amano believed that an
aquarium with a more natural appearance would be more beautiful,
easier to maintain, and would help spread a message of conservation
and love for nature. He created several aquaria with his new style,
dubbed "Nature Aquarium", which included rocks and driftwood as
composition material and utilized many varieties of plants arranged in
a random, natural manner. The release of his iconic "The Balance of
Nature" poster and his photo book Nature
Aquarium World created a
worldwide interest for the Nature
Aquarium style. Seeing the
opportunity to put his knowledge to use and make money, Amano created
Aqua Design Amano, a company that sells high-end, handcrafted goods
used to create and maintain a Nature Aquarium. Amano gained fame with
aquarium hobbyists around the world. Several massive aquarium projects
were commissioned by Japan's Sumida
Aquarium and Portugal's Lisbon
Oceanarium, which Takashi completed shortly before his 2015 death by
pneumonia. Amano's philosophy, inventions, and discoveries created
modern aquascaping and planted aquaria, which are now some of the most
common methods of aquarium decoration.
An 80-litre home aquarium
Most aquaria consist of glass panes bonded together by 100% silicone
sealant, with plastic frames attached to the upper and lower edges
for decoration. The glass aquarium is standard for sizes up to about
1,000 litres (260 US gal; 220 imp gal). However,
glass as a material is brittle and has very little give before
fracturing, though generally the sealant fails first. Aquaria are
made in a variety of shapes, such as cuboid, hexagonal, angled to fit
in a corner (L-shaped), and bow-front (the front side curves
Fish bowls are generally either made of plastic or
glass, and are either spherical or some other round configuration in
The very first modern aquarium made of glass was developed in the 19th
century by Robert Warrington. During the Victorian age, glass
aquariums commonly had slate or steel bottoms, which allowed them to
be heated underneath by an open-flame heat source. These aquariums had
the glass panels attached with metal frames and sealed with putty.
Metal-framed aquariums were still available until the mid-1960s, when
the modern, silicone-sealed style replaced them. Acrylic aquariums
first became available to the public in the 1970s.
Laminated glass is
sometimes used, which combines the advantages of both glass and
Glass aquaria have been a popular choice for many home and hobbyist
aquarists for many years. Once silicone sealant became strong enough
to ensure a long-term water-tight seal, it eliminated the need for a
structural frame. In addition to lower cost, glass aquaria are more
scratch resistant than acrylic. Although the price is one of the main
considerations for aquarists when deciding which of these two types of
aquaria to purchase, for very large tanks, the price difference tends
Acrylic aquaria are now the primary competitor with glass. Prior to
the invention of UV stabilization, early acrylic aquaria discolored
over time with exposure to light; this is no longer the case. Acrylic
is generally stronger than glass, weighs less, and provides a certain
amount of temperature insulation. In colder climates or environments,
it is easier to achieve and maintain a tropical temperature and
requires less capacity from an aquarium heater. Acrylic-soluble
cements are used to directly fuse acrylic together. Acrylic allows
for the formation of unusual shapes, such as the hexagonal tank.
Compared to glass, acrylics are easier to scratch; but unlike glass,
it is possible to polish out scratches in acrylic.
Large aquaria might instead use stronger materials such as
fiberglass-reinforced plastics. However, this material is not
transparent. Reinforced concrete is used for aquaria where weight
and space are not factors.
Concrete must be coated with a waterproof
layer to prevent the water from breaking down the concrete, as well as
preventing contamination of the water by the concrete.
Plywood can also be used when building aquaria. The benefits of using
plywood include: lower construction costs, less weight, and better
insulation. A popular positioning choice for plywood aquaria is
keeping them in a wall. Here the use of plywood is hidden by sinking
the aquarium inside the wall. Putting insulation between the two helps
with the insulation of a heated tank.
Objects used for aquariums include: coffee tables, sinks, gumball
machines and even toilets. Another such example is the
MacQuarium, an aquarium made from the shell of an Apple Macintosh
computer. In recent years, elaborate custom-designed home
aquariums costing hundreds of thousands of dollars have become status
symbols—according to The New York Times, "among people of means, a
dazzling aquarium is one of the last surefire ways to impress their
A typical kreisel tank housing several jellyfish
A kreisel tank ("kreisel" being German for "spinning top" or
"gyroscope") is an aquarium shaped like a horizontal cylinder that is
designed to hold delicate animals such as jellyfish and newborn
seahorses. These aquariums provide slow, circular water flow with a
bare minimum of interior hardware to prevent the inhabitants from
becoming injured by pumps or the tank itself. The tank has no
sharp angles around its sides and keeps the housed animals away from
plumbing. Water moving into the tank gives a gentle flow that keeps
the inhabitants suspended. Water leaves the tank through a screen
which prevents animals from being drawn into the pump intake or
There are several types of kreisel tanks. In a true kreisel, a
circular tank has a circular, submerged lid. Pseudokreisels are "U" or
semicircle shaped, usually without a lid. Stretch kreisels are a
"double gyre" kreisel design, where the tank length is at least twice
the height. Using two downwelling inlets on both sides of the tank
lets gravity create two gyres in the tank. A single downwelling inlet
may be used in the middle as well. The top of a stretch kreisel may be
open or closed with a lid. There may also be screens about midway down
the sides of the tank, or at the top on the sides. It is possible
to combine these designs; a circular shaped tank is used without a lid
or cover, and the surface of the water acts as the continuation of
Another popular setup is the biotope aquarium. A biotope aquarium
is a recreation of a specific natural environment. Some of the most
popular biotopes are the freshwater habitats of the Amazon and Rio
Negro rivers, the African rift lake environments of
Lake Malawi and
Lake Tanganyika, and saltwater coral reefs of Australia, the Red Sea,
and the Caribbean. The fish, plants, substrate, rocks, wood, coral,
and any other component of the display should completely match that of
the local natural environment. It can be a challenge to recreate such
environments, and most "true" biotopes will only have a few (if not
only one) species of fish and invertebrates.
Finally, an emerging concept for the home is that of a wall mounted
aquarium, some of which are displayed at the Living Art Marine
Aquarium size and volume
The 80-meter (260 ft) underwater tunnel in
An aquarium can range from a small glass bowl containing less than 1
litre (2.1 US pt) of water to immense public aquaria that
house entire ecosystems such as kelp forests. Relatively large home
aquaria resist rapid fluctuations of temperature and pH, allowing for
greater system stability. Beginner aquarists are advised to
consider larger tanks to begin with, as controlling water parameters
in smaller tanks can prove difficult.
Unfiltered bowl-shaped aquaria are now widely regarded as unsuitable
for most fish. Advanced alternatives are now available. In order
to keep water conditions at suitable levels, aquariums should contain
at least two forms of filtration: biological and mechanical. Chemical
filtration should also be considered under some circumstances for
optimum water quality. Chemical filtration is frequently achieved via
activated carbon, to filter medications, tannins, and/or other known
impurities from the water.
Reef aquaria under 100 litres (26 US gal;
22 imp gal) have a special place in the aquarium hobby;
these aquaria, termed nano reefs (when used in reefkeeping), have a
small water volume, under 40 litres (11 US gal;
9 imp gal).
Lisbon Oceanarium designed by architect Peter Chermayeff
Practical limitations, most notably the weight of water (1 kilogram
per litre (8.345 lb/U.S. gal; 10.022 lb/imp gal))
and internal water pressure (requiring thick glass siding) of a large
aquarium, restrict most home aquaria to a maximum of around 1 cubic
metre in volume (1000 L, weighing 1,000 kg or 2,200 lb). Some
aquarists, however, have constructed aquaria of many thousands of
Public aquariums designed for exhibition of large species or
environments can be dramatically larger than any home aquarium. The
Georgia Aquarium, for example, features an individual aquarium of
6,300,000 US gallons (24,000 m3).
A new trend is to have very small aquariums, termed mini aquariums
(less than 150 litres or 40 gallons) or nano aquariums (less than 75
litres or 20 gallons). These can be either freshwater or saltwater,
and are intended to display a tiny but self-contained
Filtration system in a typical aquarium: (1) intake, (2) mechanical
filtration, (3) chemical filtration, (4) biological filtration medium,
(5) outflow to tank
The typical hobbyist aquarium includes a filtration system, an
artificial lighting system, and a heater or chiller depending on the
aquarium's inhabitants. Many aquaria incorporate a hood, containing
the lights, to decrease evaporation and prevent fish from leaving the
aquarium (and anything else from entering the aquarium).
Combined biological and mechanical aquarium filtration systems are
common. These either convert ammonia to nitrate (removing nitrogen at
the expense of aquatic plants), or to sometimes remove phosphate.
Filter media can house microbes that mediate nitrification. Filtration
systems are sometimes the most complex component of home aquaria.
Aquarium heaters combine a heating element with a thermostat, allowing
the aquarist to regulate water temperature at a level above that of
the surrounding air, whereas coolers and chillers (refrigeration
devices) are for use anywhere, such as cold water aquaria, where the
ambient room temperature is above the desired tank temperature.
Thermometers used include glass alcohol thermometers, adhesive
external plastic strip thermometers, and battery-powered LCD
thermometers. In addition, some aquarists use air pumps attached
to airstones or water pumps to increase water circulation and supply
adequate gas exchange at the water surface. Wave-making devices have
also been constructed to provide wave action.
An aquarium's physical characteristics form another aspect of aquarium
design. Size, lighting conditions, density of floating and rooted
plants, placement of bog-wood, 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 survival of tank
An aquarium can be placed on an aquarium stand. Because of the weight
of the aquarium, a stand must be strong as well as level. A tank that
is not level may distort, leak, or crack. These are often built
with cabinets to allow storage, available in many styles to match room
decor. Simple metal tank stands are also available. Most aquaria
should be placed on polystyrene to cushion any irregularities on the
underlying surface or the bottom of the tank itself that may cause
cracks. However, some tanks have an underframe making this
A 1,200,000-litre (320,000 US gal;
260,000 imp gal) aquarium at
Monterey Bay Aquarium
Monterey Bay Aquarium in
California, displaying a kelp forest ecosystem
Large volumes of water enable more stability in a tank by diluting
effects from death or contamination events that push an aquarium away
from equilibrium. The bigger the tank, the easier such a systemic
shock is to absorb, because the effects of that event are diluted. For
example, the death of the only fish in an 11-litre
(3 US gal; 2 imp gal) tank causes dramatic changes
in the system, while the death of that same fish in a 400-litre
(110 US gal; 88 imp gal) tank with many other fish
in it represents only a minor change. For this reason, hobbyists often
favor larger tanks, as they require less attention.
Several nutrient cycles are important in the aquarium. Dissolved
oxygen enters the system at the surface water-air interface.
Similarly, 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 enough to keep these
other nutrient cycles in approximate equilibrium.
An aquarium must be maintained regularly to ensure that the fish are
kept healthy. Daily maintenance consists of checking the fish for
signs of stress and disease. Also, aquarists must make sure that
the water has a good quality and it is not cloudy or foamy and the
temperature of the water is appropriate for the particular species of
fish that live in the aquarium.
Typical weekly maintenance includes changing around 10–20% of the
water while cleaning the gravel, or other substrate if the aquarium
has one; however some manage to avoid this entirely by keeping it
somewhat self-sufficient. A good habit is to remove the water being
replaced by "vacuuming" the gravel with suitable implements, as this
will eliminate uneaten foods and other residues that settle on the
substrate. In many areas tap water is not considered to be safe
for fish to live in because it contains chemicals that harm the fish.
Tap water from those areas must be treated with a suitable water
conditioner, such as a product which removes chlorine and chloramine
and neutralizes any heavy metals present. The water conditions must be
checked both in the tank and in the replacement water, to make sure
they are suitable for the species.
The solute content of water is perhaps the most important aspect of
water conditions, as total dissolved solids and other constituents
dramatically impact basic water chemistry, and therefore how organisms
interact with their environment. Salt content, or salinity, is the
most basic measure of water conditions. An aquarium may have
freshwater (salinity below 500 parts per million), simulating a
lake or river environment; brackish water (a salt level of 500 to
30,000 PPM), simulating environments lying between fresh and
salt, such as estuaries; and salt water or seawater (a salt level of
30,000 to 40,000 PPM), simulating an ocean environment. Rarely,
higher salt concentrations are maintained in specialized tanks for
raising brine organisms.
Saltwater is typically alkaline, while the pH (alkalinity or
acidicity) of fresh water varies more. Hardness measures overall
dissolved mineral content; hard or soft water may be preferred. Hard
water is usually alkaline, while soft water is usually neutral to
acidic. Dissolved organic content and dissolved gases content are
also important factors.
Home aquarists typically use tap water supplied through their local
water supply network to fill their tanks. Straight tap water cannot be
used in localities that pipe chlorinated water. In the past, it was
possible to "condition" the water by simply letting the water stand
for a day or two, which allows the chlorine time to dissipate.
However, chloramine is now used more often and does not leave the
water as readily. Additives formulated to remove chlorine or
chloramine are often all that is needed to make the water ready for
aquarium use. Brackish or saltwater aquaria require the addition of a
commercially available mixture of salts and other minerals.
This aquarium features a heated tank and a glass-enclosed top for
warmth during winter.
Some aquarists modify water's alkalinity, hardness, or dissolved
content of organics and gases, before adding it to their aquaria. This
can be accomplished by additives, such as sodium bicarbonate, to raise
pH. Some aquarists filter or purify their water through
deionization or reverse osmosis prior to using it. In contrast, public
aquaria with large water needs often locate themselves near a natural
water source (such as a river, lake, or ocean) to reduce the level of
treatment. Some hobbyists use an algae scrubber to filter the water
Water temperature determines the two most basic aquarium
classifications: tropical versus cold water. Most fish and plant
species tolerate only a limited temperature range; tropical aquaria,
with an average temperature of about 25 °C (77 °F), are
much more common. Cold water aquaria are for fish that are better
suited to a cooler environment. More important than the range is
consistency; most organisms are not accustomed to sudden changes in
temperatures, which can cause shock and lead to disease. Water
temperature can be regulated with a thermostat and heater (or cooler).
Water movement can also be important in simulating a natural
ecosystem. Aquarists may prefer anything from still water up to swift
currents, depending on the aquarium's inhabitants. Water movement can
be controlled via aeration from air pumps, powerheads, and careful
design of internal water flow (such as location of filtration system
points of inflow and outflow).
The nitrogen cycle in an aquarium
Of primary concern to the aquarist is management of the waste produced
by an aquarium's inhabitants. Fish, invertebrates, fungi, and some
bacteria excrete nitrogen waste in the form of ammonia (which converts
to ammonium, in water) and must then either pass through the nitrogen
cycle or be removed by passing through zeolite.
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.[page needed] In the wild, the vast amount of
water surrounding the fish dilutes ammonia and other waste materials.
When fish are put into an aquarium, waste can quickly reach toxic
concentrations in the enclosed environment unless the tank is cycled
to remove waste.[page needed]
A well-balanced tank contains organisms that are able to metabolize
the waste products of other aquarium residents. This process is known
in the aquarium hobby as the nitrogen cycle.
Bacteria known as
nitrifiers (genus Nitrosomonas) metabolize nitrogen waste. Nitrifying
bacteria capture ammonia from the water and metabolize it to produce
Nitrite is toxic to fish in high
concentrations. Another type of bacteria (genus Nitrospira) converts
nitrite into nitrate, a less toxic substance. (
were previously believed to fill this role. 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.)
However, commercial products sold as kits to "jump start" the nitrogen
cycle often still contain Nitrobacter.
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 that decays more slowly than ammonia-driven plankton already
dissolved in the water.
Maintaining the nitrogen cycle
Live plants in an aquarium help to complete the nitrogen cycle, by
utilizing nitrate as fertilizer. This 60-litre aquarium contains
Anubias barteri and Echinodorus bleheri. A heater and small filter are
in the background.
What hobbyists call the nitrogen cycle is only a portion of the
complete 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. The aquarium keeper must remove water once nitrate
concentrations grow, or remove plants which have grown from the
Hobbyist aquaria often do not have sufficient bacteria populations to
adequately denitrify waste. This problem is most often addressed
through two filtration solutions:
Activated carbon filters absorb
nitrogen compounds and other toxins, while biological filters provide
a medium designed to enhance bacterial colonization. Activated carbon
and other substances, such as ammonia absorbing resins, stop working
when their pores fill, so these components have to be replaced
New aquaria often have problems associated with the nitrogen cycle due
to insufficient beneficial bacteria. Therefore, fresh water has to
be matured before stocking them with fish. There are three basic
approaches to this: the "fishless cycle", the "silent cycle" and "slow
In a fishless cycle, small amounts of ammonia are added to an
unpopulated tank to feed the bacteria. 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 develop. According to anecdotal reports, the plants can
consume nitrogenous waste so efficiently that ammonia and nitrite
level spikes seen in more traditional cycling methods are greatly
reduced or disappear. "Slow growth" entails slowly increasing the
population of fish over a period of 6 to 8 weeks, giving bacteria
colonies time to grow and stabilize with the increase in fish waste.
This method is usually done with a small starter population of hardier
fish which can survive the ammonia and nitrite spikes, whether they
are intended to be permanent residents or to be traded out later for
the desired occupants.
The largest bacterial populations are found in the filter, where is
high water flow and plentiful surface available for their growth, so
effective and efficient filtration is vital. Sometimes, a vigorous
cleaning of the filter is enough to seriously disturb the biological
balance of an aquarium. Therefore, it is recommended to rinse
mechanical filters in an outside bucket of aquarium water to dislodge
organic materials that contribute to nitrate problems, while
preserving bacteria populations. Another safe practice consists of
cleaning only half of the filter media during each service, or using
two filters, only one of which is cleaned at a time.
A very heavily stocked 19-liter aquarium containing Paracheirodon
innesi, Trigonostigma heteromorpha, and Hemigrammus erythrozonus
The biological load, or bioload, is a measure of the burden placed on
the aquarium ecosystem by its inhabitants. High biological loading
presents a more complicated tank ecology, which in turn means that
equilibrium is easier to upset. Several fundamental constraints on
biological loading depend on aquarium size. The water's surface area
limits oxygen intake. The bacteria population depends on the physical
space they have available to colonize. Physically, only a limited size
and number of plants and animals can fit into an aquarium while still
providing room for movement. Biologically, biological loading refers
to the rate of biological decay in proportion to tank volume. Adding
plants to an aquarium will sometimes help greatly with taking up fish
waste as plant nutrients. Although an aquarium can be overloaded with
fish, an excess of plants is unlikely to cause harm. Decaying plant
material, such as decaying plant leaves, can add these nutrients back
into the aquarium if not promptly removed. The bioload is processed by
the aquarium's biofilter filtration system.
Limiting factors include the oxygen availability and filtration
processing. Aquarists have rules of thumb to estimate the number of
fish that can be kept in an aquarium. The examples below are for small
freshwater fish; larger freshwater fishes and most marine fishes need
much more generous allowances.
3 cm of adult fish length per 4 litres of water (i.e., a
6 cm-long fish would need about 8 litres of water).
1 cm of adult fish length per 30 square centimetres of
1 inch of adult fish length per US gallon of water.
1 inch of adult fish length per 12 square inches of surface
Experienced aquarists warn against applying these rules too strictly
because they do not consider other important issues such as growth
rate, activity level, social behaviour, filtration capacity, total
biomass of plant life, and so on. It is better to apply the
overall mass and size of a fish per gallon of water, than simply the
length. This is because fish of different sizes produce quite
differing amounts of waste. Establishing maximum capacity is often a
matter of slowly adding fish and monitoring water quality over time,
following a trial and error approach.
Other factors affecting capacity
One variable is differences between fish. Smaller fish consume more
oxygen per gram of body weight than larger fish.
Labyrinth fish can
breathe atmospheric oxygen and do not need as much surface area
(however, some of these fish are territorial, and do not appreciate
crowding). Barbs also require more surface area than tetras of
Oxygen exchange at the surface is an important constraint, and thus
the surface area of the aquarium matters. Some aquarists claim that a
deeper aquarium holds no more fish than a shallower aquarium with the
same surface area. The capacity can be improved by surface movement
and water circulation such as through aeration, which not only
improves oxygen exchange, but also waste decomposition rates.
Waste density is another variable.
Decomposition in solution consumes
Oxygen dissolves less readily in warmer water; this is a
double-edged sword since warmer temperatures make fish more active, so
they consume more oxygen.
In addition to bioload/chemical considerations, aquarists also
consider the mutual compatibility of the fish. For instance, predatory
fish are usually not kept with small, passive species, and territorial
fish are often unsuitable tankmates for shoaling species. Furthermore,
fish tend to fare better if given tanks conducive to their size. That
is, large fish need large tanks and small fish can do well in smaller
tanks. Lastly, the tank can become overcrowded without being
overstocked. In other words, the aquarium can be suitable with regard
to filtration capacity, oxygen load, and water, yet still be so
crowded that the inhabitants are uncomfortable.
For planted freshwater aquariums, it is also important to maintain a
balance between the duration and quality of light, the amount of
plants, CO2 and nutrients. For a given amount of light, if there is
insufficient number of plants or insufficient CO2 to support the
growth of those plants, so as to consume all the nutrients in the
tank, the result would be algae growth. While there are fishes and
invertebrates that could be introduced in the tank to clean up this
algae, the ideal solution would be to find the optimal balance between
the above-mentioned factors. Supplemental CO2 can be provided, whose
quantity has to be carefully regulated, as too much CO2 may harm the
A planted freshwater aquarium
From the outdoor ponds and glass jars of antiquity, modern aquaria
have evolved into a wide range of specialized systems. Individual
aquaria can vary in size from a small bowl large enough for only a
single small fish, to the huge public aquaria that can simulate entire
One way to classify aquaria is by salinity.
Freshwater aquaria are the
most popular due to their lower cost. More expensive and complex
equipment is required to set up and maintain marine aquaria. Marine
aquaria frequently feature a diverse range of invertebrates in
addition to species of fish.
Brackish water aquaria combine
elements of both marine and freshwater fishkeeping.
Fish kept in
brackish water aquaria generally come from habitats with varying
salinity, such as mangrove swamps and estuaries. Subtypes exist within
these types, such as the reef aquarium, a typically smaller marine
aquarium that houses coral.
Another classification is by temperature range. Many aquarists choose
a tropical aquarium because tropical fish tend to be more
colorful. However, the coldwater aquarium is also popular, which
is mainly restricted to goldfish, but can include fish from temperate
areas worldwide and native fish keeping.
A saltwater aquarium
Aquaria may be grouped by their species selection. The community tank
is the most common today, where several non-aggressive species live
peacefully. In these aquaria, the fish, invertebrates, and plants
probably do not originate from the same geographic region, but
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. Most marine tanks and
tanks housing cichlids have to take the aggressiveness of the desired
species into account when stocking. Specimen tanks usually only house
one fish species, along with plants, perhaps ones found in the fishes'
natural environment and decorations simulating a natural ecosystem.
This type is useful for fish that cannot coexist with other fish, such
as the electric eel, as an extreme example. Some tanks of this sort
are used simply to house adults for breeding.
Ecotype, ecotope, or biotope aquaria is another type based on species
selection. In it, an aquarist attempts to simulate a specific natural
ecosystem, assembling fish, invertebrate species, plants, decorations
and water conditions all found in that ecosystem. These biotope
aquaria are the most sophisticated hobby aquaria; public aquaria use
this approach whenever possible. This approach best simulates the
experience of observing in the wild. It typically serves as the
healthiest possible artificial environment for the tank's occupants.
Tunnel at the Georgia Aquarium, USA
Main article: Public aquarium
Most public aquarium facilities feature a number of smaller aquaria,
as well those too large for home aquarists. The largest tanks hold
millions of gallons of water and can house large species, including
sharks or beluga whales. Dolphinaria are specifically for dolphins.
Aquatic and semiaquatic animals, including otters and penguins, may
also be kept by public aquaria. Public aquaria may also be included in
larger establishments such as a marine mammal park or a marine park.
A virtual aquarium is a computer program which uses
3D graphics to
reproduce an aquarium on a personal computer. The swimming fish are
rendered in real time, while the background of the tank is usually
static. Objects on the floor of the tank may be mapped in simple
planes so that the fish may appear to swim both in front and behind
them, but a relatively simple 3D map of the general shape of such
objects may be used to allow the light and ripples on the surface of
the water to cast realistic shadows. Bubbles and water noises are
common for virtual aquariums, which are often used as screensavers.
The number of each type of fish can usually be selected, often
including other animals like starfish, jellyfish, seahorses, and even
sea turtles. Most companies that produce virtual aquarium software
also offer other types of fish for sale via Internet download. Other
objects found in an aquarium can also be added and rearranged on some
software, like treasure chests and giant clams that open and close
with air bubbles, or a bobbing diver. There are also usually features
that allow the user to tap on the glass or put food in the top, both
of which the fish will react to. Some also have the ability to allow
the user to edit fish and other objects to create new varieties.
Cat and fishbowl, after Isoda Koryusai. Original circa 1775.
Association of Zoos and Aquariums
Association of Zoos and Aquariums (AZA)
List of aquarium diseases
List of aquarium fish by scientific name
List of brackish aquarium fish species
List of brackish aquarium plant species
List of freshwater aquarium amphibian species
List of freshwater aquarium fish species
List of freshwater aquarium invertebrate species
List of freshwater aquarium plant species
List of marine aquarium fish species
List of marine aquarium invertebrate species
List of marine aquarium plant species
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