An aquarium is a receptacle of fresh or salt water in which aquatic plants and animals are kept for study or amusement. An aquarium is usually a tank or group of tanks for the display or study of fish or other aquatic animals.
The name is also given to a large collection of aquatic plants or animals for public exhibition, commonly found in zoological or botanical gardens.
The basic requirement for keeping fish (except in small home aquariums) is to ensure the movement and treatment of large quantities of water, because the great majority of aquatic animals cannot endure the conditions that develop in small standing bodies of water. Particular requirements include filterage, clarification, temperature and chemical control, aeration, and storage. Most of these functions are performed in the operation of large aquariums, although the degree to which each is carried out may vary with local conditions. The limitations imposed by these requirements almost invariably cause any large aquarium to become a collection of relatively small tanks, each served by a circulation system isolated from that of the other tanks.
The operation of a domestic aquarium follows different principles from those governing the operation of large, institutional aquariums. The small aquariums are, by their nature, limited in the kind and number of fish that they can carry. Such aquariums work on the principle that fresh water, unless it is abused, overloaded or poisoned, will improve as it ages and continue to support any of the kinds of fish that can live in it in the first place.
Stocking the Aquarium
In stocking a public aquarium or oceanarium, the animals first must be caught unharmed and then transported safely to their destination. This move also involves the transportation of water, which is as subject to deleterious change as is water in the aquarium.
A major fallacy once governed the stocking of small fish tanks. This was the principle of the so-called "balanced aquarium". The theory was that aquatic plants could take up the carbon dioxide released by the fish and use this carbon dioxide to release the oxygen needed by the fish. This simple principle gained widespread acceptance until it was shown that only under very strong light would the plants release oxygen. At other times, the plants actually competed with the fish for the available oxygen, which was entering the water through its surface. In actual practice, a small planted tank, in comparison to a similar unplanted tank, under normal conditions will carry more fish per unit of water only if kept in bright light continuously, day and night.
Aquatic Physiology and Aquariums
By their nature, fish and aquatic invertebrates are more intimately bound to their environment than are terrestrial animals. Proportionately, aquatic animals have less blood than terrestrial animals, for instance, because they are in osmotic balance with the water surrounding them (the concentration of salts in their blood is the same as the concentration in the surrounding water solution). Consequently, the aquatic environment must be more closely controlled both in temperature and in chemical conditions than either of these need be for terrestrial creatures. Also, noxious animal wastes slowly change the water chemistry; if allowed to accumulate, the wastes will kill the aquarium's inhabitants.
In aquariums or oceanariums where ocean water is pumped into tanks and returned to the sea, and where the inhabitants are from local waters, much less control is needed than in inland aquariums. In these aquariums, water originally transported from the sea must be stored and continually recirculated.
Even in controlled aquariums, control of algae is a prime necessity because the metabolites developed by the higher organisms and by sunlight stimulate a prolific growth of algae that not only would limit visibility but also would destroy the exhibit animals. One way to control algae is to use copper, an excellent algicide. Unfortunately, many fish and invertebrates can tolerate a far smaller proportion of copper than is needed to destroy the algae.
A considerable financial saving in maintaining fresh aquarium water is possible with the use of fairly suitable synthetic seawaters. These are somewhat more limited than natural sea-waters in the kind of fish that they will support. Synthetic seawater is prepared by adding to fresh water the proper proportions of most of the chemicals normally present in seawater. Some inland aquariums use a mixture of natural and synthetic seawaters to save money.
There are many other methods for the control of tank water and for the moving of aquatic animals. Most are the result of the experience of the workers in some specific aquarium, but the variations are numerous.
Assembling a Home Aquarium
Supplies and equipment for a domestic aquarium are available in most pet stores. The essentials are a tank, some fine gravel, plants, a thermostatically controlled heater, a thermometer, a net, and fish.
The tank, of any convenient size, should be installed in a suitable permanent place near, but not very close to, a window, and out of drafts. The gravel should be washed well and placed in the tank, sloping up from front to ack. (Ore rocks or limestones should not be used in aquariums.) Some water should then be put into the tank to fill it about half way.
Plants should be planted and arranged in the back corners and along the back of the tank. Then the rest of the water should be put in without disturbing either the plants or gravel. The heater should be put into the water set to maintain a temperature of about 75° F (24° C), and plugged in. The aquarium then should be left for a day or two to establish the proper temperature and release gases in the water. Then the fish, also available at pet stores, may be placed in the aquarium, making sure that they do not undergo a change of temperature.
A close-fitting cover glass should be placed over the tank. An electric lamp should be included either as a part of the cover itself or over the glass cover.
Since 1865, about 1,000 species of fish have been imported for domestic aquariums in the United States, but only about 150 species are regularly available. About 40 species of plants also are available for domestic tanks. The remainder of the complement of candidates for the home aquarium is made up of about 20 species of snails and other shellfish, a few species of newts and salamanders, the young of several species of freshwater turtles, and a few small frogs.