ABSTRACT
Temperature varies regularly along the longitudinal profile of a water course in relation to atmospheric temperature. A species can survive between two temperature limits. Between these limits, temperature has an effect on its metabolism, duration of its biological cycle, its survival term, and its rate of reproduction. The ecological importance of heat arises from the general dependence of chemical reactions on heat: heat is the essential regulator of cellular activity. Cellular activity can occur only between two limits—the minimum and maximum temperature thresholds. In the biological cycle of a species, quiescence is a simple halt in development, immediately reversible and determined by the appearance of unfavourable conditions—essentially of temperature in the aquatic environment. Diapause is a phase of slowed-down life that is obligatory in nature, genetically determined and independent of unfavourable conditions. Diapause may appear at various stages of development, but it is most frequent during the egg stage.
