Only a few fish can adapt to life in the restricted space of a tank, but even these will die if they are not given the right surroundings.

The aquarium must be carefully prepared. On the bottom there should be a mixture of sand and pebbles to give a realistic look. Underwater plants are useful because they help to keep the water pure by absorbing waste products and providing oxygen. The water must be neither too cold nor too warm and it must not contain any harmful substances. It should seldom be completely changed or replenished. A glass cover to the aquarium is often used, to reduce evaporating and prevent the fish from jumping out.