Aquarium, some contrivance on a large or small scale for keeping aquatic animals and plants alive out of their native habitat. Though the custom of keeping fish alive in tanks (vivaria) had been for long resorted to as a matter of domestic convenience, it is only since the middle of this century that the scientific and æsthetic value of aquariums has been appreciated. The Scottish naturalist Sir John Dalyell was one of the first (from 1790 onwards) to utilise simple aquariums for scientific purposes, and the almost historic long-lived sea-anemone 'Grannie' was one of his prisoners. In 1842 Johnston described the successful establishment of a small but well-peopled aquarium. Ward, Gosse, Warrington, and others did much to make both fresh-water and marine collections practicable and popular, and though the fresh enthusiasm of thirty years ago has to some extent died away, the number of public and scientific aquariums has greatly increased. The large aquariums at Brighton and Hamburg are deservedly famous, and many others have been established both in towns for popular instruction and at the various zoological marine stations for purposes of scientific study. The first scientific and popular aquarium was that erected in the London Zoological Gardens in 1852. The Berlin Aquarium is a good instance of a well-managed collection at a considerable distance from the sea, while that in connection with the Naples Zoological Station has proved a most valuable acquisition in studying the habits and life-histories of marine plants and animals. For detailed information, the reports of the Brighton Aquarium and the Naples station should be consulted.
Fresh-water aquariums, though less decorative and interesting, are on some scale possible to every one, while the ready importation of sea-water or its artificial preparation makes it quite feasible for even inland residents to keep marine plants or animals in good condition. Since 1841 various recipes have been given for the artificial preparation of sea-water—e.g., by mixing with rather less than 4 quarts of spring-water 3½ ounces of common table-salt, ¼ ounce Epsom salts, 200 grains of chloride of magnesium, and 40 grains of chloride of potassium. Into this sea-lettuce (Ulva) and other seaweeds should first be placed. For a successful aquarium careful aeration is essential; and this is effected either simply by the aid of a syringe, or by mechanical contrivances of fountain, drip-glass, &c., and as far as possible also by regulating the proportion of plants and animals, since these compensate one another in their relations to the atmosphere. Abundant light and careful purification are also necessary. Dead specimens must be removed before decomposition, and the water filtered when it shows signs of losing its clearness and fresh smell. Concentration of the sea-water through evaporation, original impurities in the water (which is best conveyed in fir-wood or stoneware vessels), contamination by dust, overcrowding, and the like, must obviously be avoided. As to the stock, experience is the surest though slowest guide; but hints can be obtained by consulting popular works on marine plants and animals—Mr Gosse's Aquarium (1854), and more modern works, such as that of Hughes. Kingsley's Glaucus is also of permanent interest to beginners.