An aquarium is a glass or plastic box that is taped to be watertight. You can keep fish and other aquatic animals in it, but also plants. The word aqua comes from Latin and means water.
The aquarium needs a layer of sand or gravel on the bottom. After the aquarium is filled with water, you can put aquatic plants in it. Then fish, crabs, or mollusks such as snails can live in it.
The water in the aquarium always needs fresh oxygen so that the plants and animals can breathe. Sometimes it is enough to regularly replace the water with fresh water. However, many aquariums have an electric pump. She blows fresh air through a hose and then through a sponge in the water. In this way, the air is distributed in fine bubbles.
There are aquariums that are small and stand in a room and some very large aquariums, for example in the zoo. Some contain fresh water, others salt water like in the sea. Zoos that only show aquatic animals are also called aquariums.