AQUARIUM (Lat., a watering-place for cattle, from aqua, water). A tank or vessel containing, either salt or fresh water, in which either marine or fresh-water plants and ani mals are kept in a living state. _From 1854 to 1860 there was a mania for these scientific toys, and they became not only an aid to study, but a source of rational amusement, depending in principle upon the relations discovered by science between animal and vegetable life, and particu larly upon the consumption by plants miller the action of light of the carbonic-acid gas given forth by animals, and the consequent restoration to the air or water in which they live of the oxygen necessary for the maintenance of animal life. The aquarium must, therefore, contain both plants and animals, and in something like a proper proportion. Zofiphytes, annelids, mollusks, crustaceans. and fishes may thus be kept in health and their habits observed. The water must be frequently aerated, which can be accom plished by taking up portions of it and pouring them in again from a small height. The fresh water aquarium is frequently provided with a fountain. which produces a continual change of water; but even where this is the ease, the pres ence both of plants and animals is advantageous to the health of both. When sea water cannot be easily procured for the marine aquarium. a substitute may be made by mixing with rather less than 4 quarts of spring water ounces of common table salt, 1/4 ounce of epsom salts, 200 grains troy of chloride of magnesium, and 40 grains troy of chloride of potassium. With care the water may be kept pure for a long time. No dead animal or decaying plant must be permitted to remain in it. Salt water, artificially prepared, is not tit for the reception of animals at onee; but a few plants must first be placed in it, for which purpose some of the green alga?, especially species of Ulva, are most suitable. The presence of a number of mollusks, such as shore snails, is necessary for the consumption of the continually growing vegetable matter, and of the multitu dinous spores, particularly of algae, which would otherwise soon fill the water, rendering it green ish or brownish, and non-transparent, and which may be seen beginning to vegetate everywhere on the pebbles or on the glass of the tank. In a fresh-water aquarium, pond-snails, such as spe cies of Lymmea nr Planorbis, are equally indis pensable. For large aquaria, tanks of plate
glass are commonly used; smaller ones are made of bottle-glass or crystal.
Aquaria should be placed where they have sufficient access to good light. This is, of course, essential to the green plants, and will also pre vent the excessive growth of dangerous fungi. The gills of fishes, their eyes, and any wound on the body are frequently attacked by these fungi. These can often be removed in the ease of fresh water forms by a temporary bath in a common salt solution, sufficiently strong, and for a suf ficient length of time to kill the fungi. The fish, although severely affected by the salt, will revive upon being flushed with an abundance of fresh water. The plants or animals with which the aquarium is to be stocked must vary with the tastes and purposes of the individual. Among fishes, the goldfish (q.v.) stands first in beauty, variety of fantastic forms, and in tenacity of life. The stieklebacks (q.v.) are desirable be cause of their small size and their interesting nest-building and breeding habits. Besides these, many others could be added. Crabs and anemones are common objects in marine aquaria. Notable large public aquaria are maintained in various cities of Europe for the instruction and amuse ment of the people. From a scientific stand point, the aquaria at the Naples Marine Station have been of great importance. in Great Britain, the Brighton Aquarium has long been prominent, and of much service to science as well as public entertainment and instruction. in America, the United States Fish Commission Aquarium at Washington, D. C., and the New York City Aquarium are worthy of mention. The latter was installed in old Fort Clinton, on the Battery, long known as Castle Garden, where in 1897 it was perfected by Dr. Tarleton Bean, It has seven great floor-tanks, or pools, and nearly one hundred wall-tanks,lited from above and in the rear, and disposed in two tiers, the upper viewed from a gallery. Both marine and fresh water fishes and other aquatic animals are dis played, and the mechanical arrangements are of the highest excellence. it is sustained by the city, under the control of the Department of Parks, and is entirely free to the Public.