(I) Although tropical fish are delicate and must be looked after with care, the common goldfish is a fairly strong and independent creature. (II) It can survive in both cold and warm water and gets on well with members of its own species and other breeds of fish. (III) Eating anything from dry fish food to live worms, goldfish are happy to feed on the aquarium plants, if there is nothing else to eat. (IV) The fish respond to day and night, swimming energetically in bright light and resting in dimmer water. (V) Too much of this, however, can lead to nutritional deficiencies, so it is important to feed the fish regularly.