Fish are ectotherms because heat is obtained from outside the animal unlike endotherms (e.g. mammals) that generate their own body heat. Usually, the body temperature of ectotherms is close to that of their surroundings; they are often described as poikilothermic (having variable temperature).
Temperature affects all chemical and biological processes. The metabolic rate of fish doubles for every rise of 10°C. Therefore, temperature has a direct effect on important factors such as growth, oxygen demand, food requirements and food conversion efficiency. The higher the temperature, the greater the requirement for oxygen and food and the faster the growth rate.
Temperature partly determines the concentration of oxygen in water. The solubility of oxygen decreases with increasing temperature, and so concentrations are usually lower in summer.
Silver perch have a temperature tolerance range of 2 to 38°C with optimum growth occurring between 23 and 28°C. During winter when water temperatures are lower, silver perch will require less food and have a slower growth rate. At temperatures below 10°C the fish may enter a state of torpor, with greatly reduced appetite and activity. As the water temperature increases in spring and summer, the fish will require a larger quantity of food due to the increase in their metabolic rate.
Temperature also has a crucial role in stimulating silver perch gonadal maturation and spawning activity. Silver perch can be induced to breed in hatcheries when water temperatures rise to about 21°C.