Consequently, aquatic creatures will inhabit a much narrower temperature range than terrestrial animals. To keep the fish in the temperatures in which it is naturally found. To avoid any sudden fluctuations of water temperature, or introducing any fish into temperatures of more than 2 o C difference. The aquarist keeping British marine creatures usually has the find some method of cooling the water during the summer 1 . As the temperature rises, the amount of dissolved oxygen decreases.
Oxygen enters the aquarium water at the surface.
Agitation of the water surface will increase the oxygen in the water. This is so important that this is the first thing to do if a marine fish begins to look ill. Overstocking the aquaria is the commonest reason for an oxygen shortfall, as the inhabitants of the tank use up all the oxygen quicker that it can be renewed from the atmosphere and suffocate. This includes the growth of the fish, but also the increase in bacteria and micro-organisms in the filter bed that consume the waste products and remains of the food that is introduced. There is an interesting debate on this subject.