Metabolic scope and temperature
 

If the water temperature increases, the body temperature of the fish will also increase. Accordingly, the metabolism, i.e the need for oxygen, will increase as well (see red [lower] line in the diagram to the right). The difference between the routine needs and the maximum capacity is termed scope, and is a very important concept. The maximum capacity for oxygen consumption follows the blue [upper] curve in the diagram at right, and has an optimal temperature for each species. At the optimal temperature the scope is at its maximum, i.e. the animal has the highest potential to increase its oxygen consumption. If temperature increases above the optimum, then the routine needs increase, while at the same time, the maximum capacity decreases.  The result is that the aerobic scope decreases. At a certain point these two curves meet. At this point there will be no scope left for any other activity (such as swimming) as all oxygen is used for basic survival needs. In the case of long term slow temperature changes, these can sometimes be compensated for in a process called “acclimation” (see previous page).