The Encyclopedia Americana (1920)/Aquarium

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AQUARIUM (Latin, a watering-place for cattle, from aqua, water), a term applied to a tank or smaller receptacle filled with water and stocked with aquatic animals and plants for study, or, in the smaller examples, for mere beauty and interest. To maintain natural conditions, both plants and animals must be present — the plants to give off oxygen for the animals, as well as to furnish food for many of them and the animals to supply carbonic acid to the plants. With aeration and the removal of any dead animal or rotting plant, the water may be kept in good condition for a long time if supplied with a number of mollusks for the consumption of the too abundant growth of the algae and of their spores, which otherwise soon fill and discolor the water. When aquaria are placed in insufficient light noxious fungi sometimes develop in them, doing injury to the other inmates. The secret of success in conducting an aquarium in a necessarily confined space is the scientific balancing of plant and animal life, and their proper relation to the volume of water. This once accomplished, the water need never be changed. There may be a small accumulation of sediment to be removed at long intervals, and sufficient water may be added to replace that lost by evaporation. The commonest mistake (to be avoided) is overcrowding. The space in which a few animals will thrive in delightful fashion may prove a “chamber of horrors” if too many animals are placed in it There is not the same danger in an oversupply of plants, and it is better to err in this direction than to scant the provision. However, if there are too many plants, the weaker growers will begin to die off. Then either the vegetation may be reduced or another animal may be added to secure the perfect balance.

It should be remembered that in nature the only light reaching a pool comes from overhead. The artificial pool should counterfeit the natural conditions as nearly as may be. While it adds much to the pleasure to be derived from an aquarium to have it at a window so that the light may come through the sides, the ends should be dark, and in no case should the direct rays of the sun be allowed to penetrate into it. A curtain or shield which may shut out all light as high as the top of the tank is an advantage. It can be lowered when a clear view is desired.

Plants give off oxygen only under the influence of light and none at all at night. For this reason aquarium plants able to give just the needed oxygen by day are not sufficient to leave enough oxygen dissolved in the water to last the animals all night, and it is not uncommon to see the fish at the top of the water in the morning “sucking air,” even in carefully handled aquariums. This condition suggests its own remedy in the addition of one or more plants. In winter, for the same reason, the aquarium requires at least one-third more plants, the daylight being so short and the period of inaction of the oxygen producers so long.

A cubic foot of water gives room enough for not more than three fish three or four inches long. Besides these there may be two newts, which obtain a large amount of the oxygen they need by rising to the surface and filling their air sacs. Two or three tadpoles and as many water snails will be needed to act as scavengers. They clean up decayed vegetation, surplus food and the excreta of the higher animals. A crawfish and a small turtle may be added. In choosing the fish it is well to know that gold fish and all kinds of carp are not carnivorous, and so more easily fed, and there is less danger from uneaten food. The catfish and sunfish, however, are easy to keep, and specially prepared food may be bought for them. A variety of plants is desirable, but every aquarium should have several specimens of Vallisneria spiralis, noted as an abundant producer of oxygen. The marine aquarium is even more interesting than the fresh water type and falls under the same rules. Salt water fish are in general carnivorous, and while they are easily fed with bits of fish or oysters, any uneaten food rapidly decomposes and fouls the water.

All aquarium fish, but particularly those in fresh water, are subject to fungous parasites which attack their eyes, gills or any chance wound. They may frequently be cured by removal to a separate vessel in which is a large oversupply of plants, and where the light is strong on one side. Any ailing fish should receive this “oxygen cure.” The large public aquaria which exist in many cities are a great aid to students and a constant source of entertainment to the people. In America the aquarium of the United States Fish Commission at Washington and New York city aquarium are most important. The latter is under the control of the New York Zoological Society and was established in 1897 in old Fort Clinton (known for many years as Castle Garden) on the Battery. It is entirely free and has a daily average of 4,000 visitors; both marine and fresh-water animals are exhibited. In the floor are seven large pools, and the wall tanks number nearly 100. All the arrangements are the best which experience has yet suggested, and opportunities for special study of ichthyology and the natural history of marine animals are afforded. In Europe the aquarium at Brighton, England, and particularly that connected with the Marine Laboratory at Naples, are of the greatest interest and importance. Consult Smith, G. E., “The Aquarium” (New York 1900); Smith, E., “The Aquarium and How to Care for It” (New York 1902); Eggeling, O., and Ehrenberg, F., “The Fresh Water Aquarium and Its Inhabitants” (New York 1908); Verrill, “Invertebrates of Vineyard Sound,” in the annual reports of the United States Fish Commission for 1871-72; Wolf, H. T.. “Goldfish Breeds and other Aquarium Fishes” (Philadelphia 1908).

Ernest Ingersoll.