Aquarium

Marine aquarium http://en.wikipedia.org/wiki/File:Home_aqua_240_litres.png. 240 litre aquarium by Matthias Kloszczyk Creative Commons Attribution-Share Alike 2.5 Generic. 20/11/2013
240 litre aquarium by Matthias Kloszczyk

An aquarium (plural aquariums or aquaria) is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants. The term combines the Latin root aqua, meaning water, with the suffix -arium, meaning "a place for relating to".

An aquarist owns fish or maintains an aquarium, typically constructed of glass or high strength acrylic plastic. 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 to immense public aquaria. Specialized equipment maintains appropriate water quality and other characteristics suitable for the aquarium's residents.

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 allowed Romans to replace one wall of marble tanks, improving their view of the fish. In 1369, the Chinese Emperor, Hongwu, 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.

In 1836, soon after his invention of the Wardian case, 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, Felix Dujardin noted owning a saltwater aquarium, though he did not use the term. In 1846, Anna Thynne maintained stony corals and seaweed for almost three years, and was credited as the creator of the first balanced marine aquarium in London. At about the same time, Robert Warington experimented with a 13 gallon container, which contained goldfish, eelgrass, and snails, creating one of the first stable aquaria. He published his findings in 1850 in the Chemical Society's journal.

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 first large public aquarium opened in the London Zoo and came to be known as the Fish House. Philip Henry Gosse was the first person to actually use 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.

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. 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 Family 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 founded in 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.

In the 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.

Circa 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 the development of the hobby.

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 aeration. 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 aesthetic reasons.

In the United States, aquarium keeping is the second-most popular hobby after stamp collecting.In 1999 it was estimated that over nine million U.S. households own 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 percent of aquarists maintain two or more tanks.

Design

Materials
Most aquaria consist of glass panes bonded together by silicone, with plastic frames that are attached to the upper and lower edges for decoration. The glass aquarium is standard for sizes up to about 1000 litres (250 gal). However, glass as a material is brittle and has very little give before fracturing, though generally the sealant fails first. Aquaria come in a variety of shapes such as cuboid, hexagonal, angled to fit in a corner (L-shaped), and bow-front (the front side curves outwards). Fish bowls are generally either made of plastic or glass, and are either spherical or some other round configuration in shape.

The very first modern aquarium made of glass was developed in the 19th century by Robert Warrington. During the Victorian age it was common for glass aquaria to have slate or steel bottoms, which allow the aquaria to be heated underneath with an open flame heat source. The aquaria back then had the glass panels attached with metal frames and sealed with putty. These metal framed aquaria were still available on the market until the mid 1960s when the modern, silicone-sealed style displaced them. Acrylic tanks were not generally available to the public until the 1970s.

Although glass aquaria are usually preferred by aquarists over the acrylic ones because of their resistance to scratching and much more accessible price, they come with several disadvantages. Not only are they not as crack resistant as acrylic tanks but they are also nearly two times heavier than the latter. They also provide less insulation than acrylic aquaria and do not come in as many interesting shapes as these do.Many aquarists or beginners who want to get fish as pets find it particularly onerous that many online suppliers will not ship glass aquaria because of the high potential for cracking and the high weight, which increases the cost of shipping. However, glass tanks are more convenient for other aquarists because unlike acrylic, glass does not yellow over time, and also because glass tanks do not need as much support as acrylic aquaria.

Even though the price is one of the main aspects which is taken under consideration by aquarists when willing to purchase one of these two types of aquaria, when it comes to very large tanks the price difference tends to disappear.

Acrylic aquaria are also available and are the primary competitor with glass. Acrylic aquariums are stronger than glass, and much lighter. Acrylic-soluble cements are used to directly fuse acrylic together (as opposed to simply sealing the seam). Acrylic allows for the formation of unusual shapes, such as the hexagonal tank. Compared to glass, acrylics are easy to scratch; but unlike glass, it is possible to polish out scratches in acrylic.

Laminated glass is sometimes used, which combines the advantages of both glass and 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 prevent contamination from the concrete.

Styles
Aquariums have been fashioned into coffee tables, sinks, 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 peers."

A kreisel tank is a circular aquarium designed to hold delicate animals such as jellyfish. These aquariums provide slow, circular water flow with a bare minimum of interior hardware, to prevent delicate animals from becoming injured by pumps or the tank itself. Originally a German design (kreisel means spinning top), the tank has no sharp corners, and keeps the housed animals away from the plumbing. Water moving into the tank gives a gentle flow that keeps the inhabitants suspended, and water leaving the tank is covered by a delicate screen that prevents the inhabitants from getting stuck. There are several types of kreisel tanks. In a true kreisel, a circular tank has a circular, submerged lid. Pseudokreisels have a curved bottom surface and a flat top surface, similar to the shape of either a "U" or a semicircle. Stretch kreisels or Langmuir 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 circular flow. It is now possible to start a jellyfish aquarium at home as easily as a regular fish tank.

Another popular setup is the biotope aquarium. A biotope aquarium is a recreation of a specific natural environment. Some of the most popular biotopes (to name only a few) are the Amazon river, Rio Negro River, Lake Malawi, Lake Tanganyika, and Lake Victoria. The fish, plants, substrate, rocks, wood, and any other component of the display should match that of the natural environment. It can be a real challenge to recreate such environments and most "true" biotopes will only have a few species of fish (if not only one) and invertebrates.

Aquarium size and volume
An aquarium can range from a small glass bowl containing less than a litre (34 fl.oz.) 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.

Unfiltered bowl-shaped aquaria are now widely regarded as unsuitable for most fish. Advanced alternatives are now available. Aquariums should contain three forms of filtration: biological, mechanical and chemical to keep water conditions at suitable levels.

Reef aquaria under 100 litres (20 gal) have a special place in the aquarium hobby; these aquaria, termed nano reefs (when used in reefkeeping), have a small water volume.

Practical limitations, most notably the weight (one litre of fresh water has a mass of 1 kilogram (8.3 lb gal-1), and salt water is even denser) and internal water pressure (requiring thick glass siding) of a large aquarium, keep most home aquaria to a maximum of around 1 cubic metre in volume (1,000 kg or 2,200 lb). Some aquarists, however, have constructed aquaria of many thousands of litres.

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 8,100,000 US gallons (30,700 m3).

Components

Drawing of transparent 3-dimensional rectangle with two boxes and one cylinder above it and one longer, thin cylinder within it. Arrows point from the rectangle long cylinder to the top box, from the top box to the lower box, from the lower box to the other cylinder, from that cylinder back to itself, and from the cylinder to the rectangle.

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, to decrease evaporation and prevent fish from leaving the aquarium (and anything else from entering the aquarium). They also often hold lights.

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 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, that 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 inhabitants.

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. However, some tanks have an underframe making this unnecessary.

Aquarium maintenance

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 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. 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 or via 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 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, on a daily basis. 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 20% of the water while cleaning the gravel, or other substrate if the aquarium has one. A good habit is to replace the water extracted while "vacuuming" the gravel as this will eliminate uneaten foods and other residues that settle on the substrate. Tap water is not considered to be safe for fish to live in because it contains chemicals that harm the fish, so any tap water used must be treated with a suitable water conditioner, such as a product which removes chlorine and chloramine, and neutralises any heavy metals present. The water parameters must be checked both in the tank and in the replacing water, to make sure they are suitable for the species of fish kept.

Water conditions
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 countries 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.

More sophisticated 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.

Water temperature determines the two most basic aquarium classifications: tropical vs. 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).

Nitrogen cycle
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 acidic water) and 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.

The process
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. Nitrite is toxic to fish in high concentrations. Another type of bacteria, genus Nitrospira, converts nitrite into nitrate, a less toxic substance. (Nitrobacter bacteria 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.) 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
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 nitrates.

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 regularly.

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 growth".

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.

The largest bacterial populations are found in the filter; 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.

Aquarium supplies
A way to keep the aquarium clean and fresh is by using specific aquarium cleaning supplies. These may include cleaning agents especially designed to clean the water and keep it fresh, nets, algae magnets and scrapers, algae pads, brushes, gravel cleaners, sealant and tongs and grabbers. A properly cleaned aquarium means healthy and happy fish. Aquarium cleaning must be performed on a regular basis to ensure that the fish are healthy. Also, by maintaining a clean aquarium one makes sure the tank looks appealing to the visitors.

Nets are very important cleaning supplies because they are helpful in transferring the fish to breeders or refugiums or to take them out of the aquarium whenever a thorough cleaning is needed. Nets come in a variety of sizes and designs. The size one needs depends on the size of the tank they need to clean.

The cleaning liquid agents are substances especially designed to clean the water without harming the health of the fish. Cleaning agents also include scratch removers, lime dissolvers, glass and acrylic polishers, wipes, salt creep removers and magnetic cleaners. All of these are intended to be used on the tank, ornaments and equipment.

Aquarium pest control products may be needed for cleaning aquaria with corals or live rocks. Aquarium pest control is helpful in fighting infestations with different organism coming from new fish or from the plants, corals or rocks that are recently acquired. If not taken care of, infestations like this may cause damage to the aquarium by depleting resources and causing illness.

The water cleaners are amongst the first aquarium cleaning supplies that must be purchased. Aquarium water conditioners and additives like chlorine removers and stress relievers make tap water safe for use in aquariums, and should be used when preparing for tank setup or water changes. The "new tank syndrome" may be avoided if using cycle aids to establish the nitrogen cycle. Also, creating the natural water conditions for an aquarium implies getting aquarium salt, vitamins and supplements.

The level of ammonia in the water must be closely monitored as a too high level of ammonia in the water may cause the death of the fish. The market provides especially designed ammonia removers which transform ammonia into a non-toxic form until the filter is able to process it. Aquarists are recommended to have ammonia removers around for immediate use in case of ammonia emergency.

Water clarifiers are used to clean up the water that might get foamy or cloudy due to chemicals or biological blooms. Overfeeding or fish death can lead to a sudden increase in organic waste which may result in biological clouding. Water clarifiers are useful in these cases. However, they should not be needed too often because excessive clouding can mean that the filters or filter media are not working properly and should be changed.

Excessive algae and cyanobacteria can be removed with the help of algaecides. Although algaecides are the fastest way to solve problems caused by algae they are not recommended in reefs, planted tanks or in those with crustaceans or livebearers. Algaecides are also not a long term solution for this type of issue and aquarists are advised to avoid direct sunlight or lights that are not intended for aquariums on their tanks because they cause algae blooms.

The cleaning supplies that are fluid such as the water purifiers or conditioners are not to replace the thorough cleaning that should be performed at least once in two weeks. However, they are handy supplies to keep the fish healthy until the aquarist can find the right time to perform such a cleaning.

Biological loading
Biological load 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.

Calculating capacity
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 surface area.
  • 1 inch of adult fish length per gallon of water.
  • 1 inch of adult fish length per 12 square inches of surface area.

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, surface area of plant life, and so on. 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 comparable size.

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. 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.

General aquarium description (freshwater)
Identifying care methods that work for all aquarists is extremely difficult as there are several maintenance routines frequently used that have proven successful for keeping aquarium fish. However, there have been some studies done on freshwater aquarium systems that do indicate successfult trends in aquarium care. According to one study in particular that polled data from one hundred freshwater aquarists, the median/average conditions of the freshwater aquarium were described as follows:

  • Median Tank Size: 37 Gallons (inconclusive)
  • Median Stocking Density: 13 Fish at 2 Inches Each (more being worse with regard to lethality but not necessarily efficiency)
  • Median Water Change Frequency: 7 Days (inconclusive, no trend)
  • Median Water Change percentage: 30% (very large water changes may be detrimental to efficiency, but not lethality)
  • Median Lighting Wattage: 40 Watts (more watts being better)
  • Median Plantedness: Moderately Planted (more plants being better if appropriately cared for)
  • Average Snail Presence: 53% (snails seem to be associated with better efficiency and lower lethality)
  • Average Fertilizer Presence: 48% (fertilizers seem to function like snails)
  • Best Overall Filter Type: Canister (hang-on-back filters are the most prevalent, worst filter type with regard to lethality while hang-on-back with additional bio-filtration filters are the most prevalent, worst filters with regard to efficiency)

The above list represents the midpoints of freshwater aquarium dynamics, meaning that freshwater aquariums that are close to these parameters are likely to be at least moderately successful. Nonetheless, the study did confirm that some extreme parameter configurations were successful despite not being close to these parameters.

Aquarium classifications

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 marine ecosystems.

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 a 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 mangroves 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.

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 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.

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 public aquarium (plural: public aquaria or public aquariums) is the aquatic counterpart of a zoo, housing living aquatic species for viewing. Most public aquaria feature tanks larger than those which could be kept by home aquarists, as well as smaller tanks. Since the first public aquariums were built in the mid-19th century, they have become popular and their numbers have increased. Most modern accredited aquaria stress conservation issues and educating the public.

History
The first public aquarium was opened in London Zoo in May 1853; the "Fish House", as it came to be known, was constructed much like a greenhouse. P.T. Barnum quickly followed in 1856 with the first American aquarium as part of his established Barnum's American Museum, which was located on Broadway in New York before it burned down. In 1859, the Aquarial Gardens were founded in Boston. A number of aquaria then opened in Europe, such as the Jardin d'Acclimatation in Paris and the Viennese Aquarium Salon (both founded 1860), the Marine Aquarium Temple as part of the Zoological Garden in Hamburg (1864), as well as aquariums in Berlin (1869) and Brighton (1872).

The old Berlin Aquarium opened in 1869. The building site was to be Unter den Linden (along a major avenue), in the center of town, not at the Berlin Zoo. The aquarium's first director, Alfred Brehm, former director of the Hamburg Zoo from 1863 to 1866, served until 1874. With its emphasis on education, the public aquarium was designed like a grotto, part of it made of natural rock. The Geologische Grotte depicted "the strata of the earth's crust". The grotto also featured birds and pools for seals. The Aquarium Unter den Linden was a three-story building. Machinery and water tanks were on the ground floor, aquarium basins for the fish on the first floor. Because of Brehm's special interest in birds, a huge aviary, with cages for mammals placed around it, was located on the second floor. The facility closed in 1910.

The Artis aquarium at Amsterdam Zoo was constructed inside a Victorian building in 1882, and was renovated in 1997. At the end of the 19th century the Artis aquarium was considered to be state-of-the-art, as it was again at the end of the 20th century.

The oldest American aquarium is the National Aquarium in Washington, D.C., founded in 1873. This was followed by the opening of other public aquaria: San Francisco (Woodward's Garden, 1873 - 1890), Wood Hole (Science Aquarium, 1885), New York (Battery Park, 1896 - 1941), La Jolla (Scripps, 1903), Detroit (Belle Isle, 1904 - 2005), Philadelphia (Fairmount Water Works, 1911 - 1962), San Francisco (Steinhart Aquarium, 1923), Chicago (Shedd Aquarium, 1929). For many years, the Shedd Aquarium in Chicago was the largest aquarium in the world, until the Georgia Aquarium in Atlanta opened. Entertainment and aquatic circus exhibits were combined as themes in Philadelphia's Aquarama Aquarium Theater of the Sea (1962 - 1969) and Camden's re-invented Adventure Aquarium 2005, formerly the New Jersey State Aquarium (1992).

The first Japanese public aquarium, a small freshwater aquarium, was opened at the Ueno Zoo in 1882.

In 2005, the Georgia Aquarium, with more than 8 million US gallons (30,000 m3; 30,000,000 liters) of marine and fresh water, and more than 100,000 animals of 500 different species opened in Atlanta, Georgia. The aquarium's notable specimens include whale sharks and beluga whales.

Current public aquaria
Modern day aquarium tanks can hold millions of liters of water and can house large species, including dolphins, sharks or beluga whales. This is accomplished though thick, clear acrylic glass windows. Aquatic and semiaquatic mammals, including otters, and sealsare often cared for at aquaria. Some establishments, such as the Oregon Coast Aquarium or the Monterey Bay Aquarium, have aquatic aviaries. Modern aquaria also include land animals and plants that spend time in or near the water.

For marketing purposes, many aquaria promote special exhibits, in addition to their permanent collections. Some have aquatic versions of a petting zoo. The Monterey Bay Aquarium has a shallow tank filled with common types of rays which visitors are encouraged to touch. The South Carolina Aquarium opens a new exhibit in March of 2011 where you can actually feed stingrays.

Logistics
Most public aquaria are located close to the ocean, for a steady supply of natural seawater. An inland pioneer was Chicago's Shedd Aquarium that received seawater shipped by rail in special tank cars. The early (1911) Philadelphia Aquarium, built in the city's disused water works, had to switch to treated city water when the nearby river became too contaminated. Similarly, the recently opened Georgia Aquarium filled its tanks with fresh water from the city water system and salinated its salt water exhibits using the same commercial salt and mineral additives available to home aquarists. The South Carolina Aquarium pulls the salt water for their exhibits right out of the Charleston harbor.

In January 1985, Kelly Tarlton began construction of the first aquarium to include a large transparent acrylic tunnel, Kelly Tarlton's Underwater World in Auckland, New Zealand. Construction 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.

Activities
Public aquaria are often affiliated with oceanographic research institutions or conduct their own research programs, and sometimes specialize in species and ecosystems that can be found in local waters. For example, the Vancouver Aquarium in Vancouver, BC is a major center for marine research, conservation, and marine animal rehabilitation, particularly for the rich ecosystem of the Pacific Northwest. The Vancouver Aquarium was the first aquarium to capture and display an orca whale, Moby Doll, for 3 months in 1964; as well as belugas, narwhals and dolphins. None of these whales has ever left the aquarium alive, with the exception of Bjossa, a female orca who was sent to SeaWorld San Diego in April 2000 and died shortly afterward in October 2001.