It is known that fish are cold-blooded, meaning that their body temperature automatically adapts to the temperature of the surrounding environment, and this affects the increase or decrease in the percentage of vital activities. The process of laying eggs for most types of fish and also controls the time in which the eggs hatch from their larvae and the speed of the growth of those larvae into adult fish. For example, we find that warm water fish reach a length of 30 cm within two years when they are in warm water, but it takes three years to reach the same size And weight when you live in colder waters, and the temperature of the medium is a factor affecting the distribution of fish in it, so fish breeders must monitor the water temperature permanently to avoid the problems that arise from that, as the sudden change in water temperature is harmful to the vital work in the fish body. In general, thermal zones can be divided into two main zones: the first is the endurance zone, in which fish live in an absolute and unlimited manner; The second is the resistance zone, in which the fish can withstand the thermal regime of a limited area and the immediate death of the fish occurs outside this zone. Of course, the thermal shock becomes more pronounced as the temperature difference increases. Also, the acclimatization time depends to a large extent on the temperature difference. It may sometimes be advised to conduct thermal acclimatization before the transfer based on the available information, so that this process can be carried out in the optimum manner and over an appropriate time period, especially if the temperature difference is large. Therefore, the sudden thermal change has its harmful effects, as it does not allow the functions of the body to adapt to this temperature change without the occurrence of stress commensurate with the temperature change. Temperature change in the range of 5 °C or more requires several hours of acclimation for most warm-water fish, although fish vary in their ability to tolerate temperature differences. The aforementioned thermal tolerance limits must be taken into account. For example, the sensitivity of comb fish (particularly Oreochromis niloticus) to low temperatures, which greatly limits some farming practices at certain times. In open ponds that depend on surface waters in temperate climates, these fish are not directly handled (which are often dispersed) in farming practices from transport or storage until the temperature rises to a safer level.