(1) A vessel for keeping and raising aquatic animals and plants. The design, shape, and dimensions of aquariums vary greatly according to their purpose and the conditions necessary for maintaining the various items. Aquariums are made either completely of glass or with a metal frame and glass walls; they are sometimes made of plexiglass. As a rule, aquariums are rectangular, of a standard type—that is, equal in height and width, and with a length 1.5 times as long. Sometimes the height is greater than the width; such an aquarium with a beveled front glass is called a “picture tank” and is usually hung on the wall.
An essential condition for keeping fish in an aquarium is water with a definite oxygen saturation and a required salt composition. Aquatic plants are placed in aquariums to saturate the water with oxygen. The aquarium should be illuminated 10–12 hours a day. In the light the plants absorb carbon dioxide given off by the fish and produce oxygen; at the same time, the plants assimilate organic and inorganic matter from the water. In such an aquarium, it is merely a matter of removing the accumulated deposits from the bottom, cleaning the glass, and adding settled water to replace the evaporated water.
In aquariums of scientific institutions and in transporting aquarium fish, the water is saturated with oxygen by an aerator and is cleaned by filtering it through sand and activated charcoal. It is best to use well-washed gray river sand (particles 2–4 mm in size) as a lining for the bottom of the aquarium.
Plants kept in aquariums include those that float on the surface of the water (such as floating liverwort, floating moss, and water lettuce), those that float under the water (such as elodea, water milfoil, and false loosestrife), and rooted plants (such as eel grass, arrowhead, Cape pond-weed, cryptocoryne, and plants of the genus Echinodorus).
The top of the aquarium is partially covered with glass. The presence of an aquarium in a room raises the humidity of the air, a fact which is particularly useful in homes with central heating.
(2) Special institutions in which examples of marine and freshwater fauna and flora are kept for study and display. They are found in many nations of the world. In the USSR large aquariums are found in the zoos of Moscow, Tallin, Tashkent, and Riga. Aquariums for marine animals are usually located on the seacoast. Such aquariums were first created in the second half of the 19th century (in 1871 in Sevastopol’; in 1872 in Naples). Some marine aquariums are called oceanariums.
M. N. IL’IN