tradition. If fish are fed and then abruptly transferred to water colder by 8°C or more, their digestive processes will slow down or stop. Underneath these situations fish might die, exhibiting symptoms of paralysis of the respiratory and cardiac muscle grops.
This generalisation applies notably to heat-water fish. Rare examples of thermophilic pathogens exist, and the main class of extremophilic animal pathogens includes psychrophilic and psychrotrophic microorganisms that trigger fish diseases, e.g. Flavobacterium psychrophilum, Moritella viscosa, Aliivibrio wodanis and Aliivibrio salmonicida. The only tpe of life, bacteria and algae, most likely started to grow less than four billion years ago.