AQUARIUM (plural aquaria), a name given to a receptacle or institution in which living aquatic animals and plants are kept.
The term may be applied to a show-place exhibiting aquatic specimens with the ob ject of entertaining or instructing the pub lic, or it may be used to describe such a domestic toy as a bowl containing goldfish.
Certain aquaria are purely scientific insti tutions designed for the study of physio logical and biological problems. Of these the best known are those at Plymouth, Eng land, and Naples, Italy, where, apart from numerous small tanks in laboratories for the use of research workers, there is in each case a public aquarium attached, in which the exhibits are at the disposal of the students for the purpose of observation and experiment. At the Marine Biological Station at Plymouth, which receives grants from the Government and the Fishmongers' Company, a number of biolo gists are definitely retained for the purpose of studying the habits and life histories of the marketable inhabitants of the ocean.
In the case of large aquaria situated near the shore, the water, which can be continually replenished, is pumped from the sea in to reservoirs usually situated in the basements of the institutions. After being allowed to settle, it is pumped direct into the tanks containing the specimens. Where, however, the aquaria are located inland, special care must be taken to keep the water pure and clear and to prevent the overflow from the tanks running to waste.
The most up-to-date inland aquarium is that of the Zoological Society of London in Regent's Park, which was opened in 1924. In the case of this institution, which, whilst encouraging the scien tific study of aquatic life, caters for the entertainment of the public, the sea-water was brought from the Bay of Biscay. Both the fresh-and salt-water in the aquarium are prevented from be coming stagnant by a system of continual circulation, being pumped from the underground reservoirs, having in the case of the fresh-water a 6o,000 gallon capacity, and in the case of the salt-water a 125,00o gallon capacity, to other reservoirs situated in the mountains of the Mappin Terraces, about Soft. above the exhibition tanks. From the high level reservoirs the water falls by gravity into the show tanks, the overflows passing through a series of sand filters before returning to the main storage reser voirs in the cellars of the building. The efficient oxygenation of the water is obtained by passing compressed air directly into the show tanks, and by discharging the water feeding these tanks with great force through a nozzle with a narrow aperture, the resulting bubbles producing the effect of a smoke cloud. The purity of the sea-water is also ensured by a discreet choice of the metals used in the manufacture of the piping and in the construction of the tanks. Should, for instance, copper or zinc come into contact with the sea-water of an aquarium the exhibits die speedily of metallic poisoning. The piping in the Society's aquarium is formed of chemically pure lead, or of iron lined with glass enamel. The ex hibition tanks, the three largest of which hold 5,000 gallons, are constructed of slate or concrete, and are decorated with rocks. The thickness of the glass used for the fronts of the large tanks is 1 yin. Aquatic animals are easily killed by sudden changes in temperature. The Zoological Society's aquarium has elaborate heating and refrigerating systems which keep the tanks in the temperate fresh-water and marine aquaria at a temperature of about 60°F. throughout the year. The majority of the tropical aquaria are kept at a uniform temperature of 75° to 80°F.
In an aquarium where it is not possible to replace the water continually, artificial aids must be sought to remove pollution, which, owing to the excess in number of fish per unit volume compared with the sea or river, cannot be coped with by natural means. In the Regent's park aquarium, before the water is cleaned by being passed through a series of filters, most rejected food, ex crement, etc., which is easily detected on the sandy floors of the tanks, is removed daily by means of a suction pipe. Filtration is further responsible for the removal of suspended organic matter and phosphates. Aeration oxidizes ammonia and organic matter in solution. Storage in the dark kills the noxious bacteria.
The guiding principles to be observed in the management of a large aquarium apply with equal force to the miniature home aquarium. Anyone wishing to maintain a small aquarium stocked with suitable marine specimens should, apart from aerating the water, circulate and filter it. This may be effected by means of a syphon pipe emptying the water from a small high level tank into the exhibition tank likewise fitted with a syphon, which slowly empties the water into a low level tank of ter filtering through a flower pot filled with sand. When the lower tank is full the water it contains is emptied into the high level tank which should be of equal capacity. On the size of the syphon pipes depends the rate of the flow of the water, which can be controlled to last to or more hours according to the requirements of the specimens. In the event of the aquarist experiencing difficulty in obtaining water in sufficient quantity from the coast, there should be no difficulty in his manufacturing his sea-water at home. The following for mula has been tested in the Marine Biological Association's lab oratories, and found to give satisfactory results:—Common salt, oz.; potassium chloride, t+ oz.; calcium chloride (dry), 2 oz.; magnesium chloride (crystals), 84 oz.; magnesium sulphate (crys tals), Ili oz. ; bicarbonate of soda, oz.
The above should be mixed with io gal. of soft water to which should be added, after mixing, -k oz. of potassium nitrate, io grains of sodium phosphate, 5 grains of chloride of iron and gal. of natural sea-water. The reason for adding a small quantity of natural sea-water is that sea-water contains a certain mysterious ingredient which has up to the present defied analysis, but may be considered analogous to what is known as vitamins in food. Its entire absence would result in the specimens in the aquarium developing disease in a comparatively short period.
An aquarium tank should present the greatest possible surface of water to the air in proportion to its size and depth. The popular goldfish bowl is to be condemned as admitting too little air for the well-being of its inhabitants. Square, metal-framed, slate bottom, glass-sided aquaria are best. With regard to size, the aquarist wishing to keep such comparatively hardy fish as goldfish, carp, tench, orfe, perch, etc., should allow one gallon of water to every inch of fish. Delicate forms such as trout require double that amount of water.
In setting up a small private aquarium, which should be so placed that it receives not more than one hour of direct sunlight a day, the floor should be covered with about gin. of well-washed gravel or sand before filling with water and planting. Plants are necessary for keeping the balanced fresh-water aquarium in a healthy condition, as they not only oxygenate the water but ab sorb the carbon dioxide given off by the fishes. The following plants are specially suitable for the aquarium :—Eel Grass (V alis neria spiralis), Arrowhead (Sagittaria natans), Swamp Grass (Ludwigia palustris), Fanwort (Cabomba caroliniana), Ditchmoss (Anacharis canadensis), Water Milfoil (Myriophyllum verticilla tum) and Stonewort (Nitella gracilis). The small aquarium should have a light glass cover to keep out the dust and prevent the fishes from jumping out. If the aquarium receives daily attention the water need be changed only very rarely. Special care should be taken to ensure that any new water added is of the same tem perature as the old. Fish should be transported from their native elements to the aquarium in receptacles that are broader than deep. In the case of trout which require much aeration a grid of perforated galvanized iron should be fixed in the travelling tank about Sin. from the bottom, forming a false bottom on which the fish can lie without the risk of clouding the water by the disturb ance of excretory and other noxious products. On arrival at their destination the fish should not be immediately transferred to the aquarium, but the water in the carriers should be slowly replaced by the water of the exhibition tank. In the aquarium fresh-water fish are victims to various ailments. The most com mon is a very virulent and highly contagious fungoid disease, popularly known as salmon disease. This, which often results from sudden changes in the temperature of the water, is due to bacteria (Saprolegnia ferox) and first shows itself in the form of a whitish film which coats the outside of the fish. At a later stage it attacks the gills and causes the victim to die df asphyxiation. The victim may often be cured if treated in the early stages of the disease. The best remedy is to introduce common rock salt, or preferably sea-water, into the aquarium, a suitable quantity of salt being one oz. to each gallon of water. If sea-water is used, one part should be introduced for four parts of fresh-water. As the fish recovers, the strength of the solution should be very gradually reduced. It is important not to overfeed, and fish con fined in small aquaria should always be on the alert for a meal. One meal a day suffices, care being taken not to introduce more food than can be devoured by the inhabitants in the course of an hour. With regard to the question of variety of foods, the ma jority of large fish should be supplied with bullocks', sheep's or horses' heart, liver, earthworms, prawns and shrimps. Small fish will flourish on a diet consisting of the crustacea Gammarus and Daphnia, enchytrae worms, the larvae of the common gnat, hard boiled yolk of egg and fresh ants' eggs. Goldfish and other mem bers of the carp family may be given biscuit and should also be provided with a small quantity of lettuce or other green food. Newly-born fish after the absorption of their yolk sac feed on in fusoria which can easily be produced in a day or two by an infusion of vegetable matter. (E. G. Bo.) The United States.—The principal public aquaria of the United States are at Boston, Chicago, Detroit, Honolulu, New Orleans, New York city, Philadelphia, San Francisco and Wash ington. The aquarium in New York is maintained by the city, its management being in the hands of the New York Zoological Society which provides all exhibits from its private funds. The Boston and Detroit aquaria are municipal institutions con trolled by park departments. The aquarium in San Francisco, built with private funds and controlled by the California Academy of Sciences, is maintained by the city. The aquarium in New Orleans was privately built, is in a public park and is managed by a zoological society. The smaller aquarium in Washington is maintained by the Bureau of Fisheries in a Government build ing. It was long the custom of the national Bureau of Fisheries to operate excellent temporary aquaria at industrial exposi tions and these were highly successful. A few of the aquarium buildings were architecturally beautiful. At the world fairs of Chicago, Atlanta, St. Louis, Buffalo, Omaha, Charleston, Nash ville and other cities the aquarium attracted more visitors than any other single exhibit. The larger permanent aquaria usually attract the attention of the people more than do zoological gar dens or museums of natural history or art. The collections consist of living marine and fresh water animals. It is the character of the exhibits which determines the cost of maintenance. An aqua rium with exhibition tanks requiring nothing more complicated than mere connections with a city water system, can obviously be operated at less expense than one requiring pumps for the circulation of sea water. It would be possible for any inland city not too remote from suitable collecting waters to maintain exhibits of fresh water fishes and amphibians at small cost as compared with marine forms requiring stored sea water. The flow of fresh water being automatic, the equipment for operation can be re duced to very simple terms.
For marine exhibits, the equipment and maintenance are far more costly. The piping, if for permanent use with salt water, is specially constructed of vulcanized rubber, lead or other non-rusting material, with valves and other fittings to match. An underground reservoir for the storage of sea water is neces sary, together with rust-proof pumps of bronze for its circu lation. Filters are required to clear the water flowing back to the reservoir. For pumps which must run night and day there is necessarily an increase in the number of employes, some of whom, such as mechanicians, require special compensation. For tropical forms of life water-heating equipment is required to insure their safety in winter. For northern forms of life cold water is equally necessary in summer. A large aquarium in the latitude of New York, for instance, requires a complicated equipment if its aquatic exhibits include both northern and tropical fresh water and marine forms. The construction of a reservoir for pure sea water is imperative, even if the aquarium be located on the sea shore. Experience has shown that the water supply must be maintained in uniformly good condition, unaffected by storms, changes in salinity, winter and summer temperatures, and the im purities of harbours. Unfavourable variations in the water supply cannot be avoided where water is pumped directly from the sea. The prime requisite for aquatic animals in captivity is a plentiful supply of their natural element, to which everything else is subor dinate. The water supply must be pure and abundant, both for marine and for fresh water exhibits. The fresh water supply of most cities is good enough for aquarium purposes as it comes from the pipes, but during long continued rains or necessary alterations of the system the water may become murky and remain so for weeks. Suitable filters are therefore necessary to insure the clear ness of water desirable for exhibition purposes. Filters for fresh water are installed to receive the water before it is delivered to exhibition tanks. In the case of permanently stored sea water, filters are also necessary, but they are installed so as to receive the drainage of the exhibition tanks and return the water to the reservoir clear and free from the impurities created by the feeding of animals. City waters that are treated with chlorine are not suitable for aquarium purposes.
All equipment tending to facilitate the distribution of stored water and to preserve its purity is desirable, because its vitiation, even in small degree, may result in serious losses of animal life. Lack of food can be long endured by aquatic animals but the im pairment of their natural element is immediately fatal, whether from actual fouling or mere lack of oxygen. They may long sur vive overcrowding if the supply of water is abundant. The col lecting of aquatic animals, with the exception of mammals, involves their transportation in weighty tanks of their natural element, which moreover must be kept pure in transit. Aquatic animals must reach their destination not merely alive, but able to endure the conditions of captivity, which are always more or less unfavourable to wild creatures.
The exhibits of a public aquarium are popularly supposed to consist chiefly of fishes, aquatic reptiles and some of the more conspicuous invertebrates, but this conception is a narrow one. The name aquarium admits of a much more comprehensive inter pretation. The collections of an ideally equipped establishment for the exhibition of living aquatic forms might properly include representatives of the entire aquatic fauna and flora, so far at least as the forms selected are capable of living in shallow water.
See C. H. Townsend, The Public Aquarium, Its Construction, Equip ment and Management (1928) ; C. W. Coates, Tropical Fishes for a Private Aquarium (1933) ; W. T. Innes, Exotic Aquarium Fishes (1935) . (C. H. To.)