Some fish can survive in very hot or cold waters because they have developed specific physiological adaptations such as the ability to regulate their own body temperature, modify their metabolism, or produce antifreeze proteins to withstand extreme temperatures.
In certain fish living in extreme cold, such as Antarctic fish, there are proteins in their blood called antifreeze proteins. These proteins prevent the formation of ice crystals inside their bodies, much like antifreeze in your car's radiator. In contrast, fish from hot springs have adapted proteins that withstand high temperatures without losing their function. Moreover, the particular composition of cell membranes in these fish allows them to remain fluid and functional even when it is extremely hot or cold: these membranes adjust their concentration of specific fats (lipids), keeping their appearance flexible like oil that does not harden in the cold. Some fish also possess a highly efficient specialized circulatory system with thermal exchanges between blood vessels, enabling them to maintain certain sensitive parts of their bodies (like the brain or eyes) at a more favorable temperature, ensuring clear thinking even when it’s freezing outside.
Some fish avoid extreme temperatures either by migrating to more temperate areas or by moving vertically in the water column. Some, for example, dive deep in case of high heat, where the water is cooler. Others tend to take refuge in less exposed areas, such as in the shade of a rock or near the seabed. Those facing intense cold can slow down their activity to almost hibernation: their bodies then operate in slow motion to conserve the available energy as much as possible. Not foolish, these fish sometimes also practice very tight schooling to stay warm together. Finally, some use an astonishing trick: they change their feeding habits and store more energy in the form of fat, a true natural thermal insulator that protects them from freezing temperatures.
In extreme environments, the Antarctic icefish is a true champion: its blood is transparent, without red blood cells. It produces a type of natural antifreeze, special proteins that prevent its body from freezing even in negative temperatures. At the other end of the thermometer, fish of the Cyprinodon genus swim comfortably in hyper-hot desert waters (up to about 45°C). Their enzymes function at full capacity despite the heat, allowing them to survive where most other fish would turn into soup. Even more astonishing, some deep-sea fish live near hydrothermal vents, where water reaches extreme temperatures at depth: guaranteed success thanks to their hyper-resistant cellular mechanisms.
Genetics plays a major role in how fish cope with extreme temperatures. Some species have specific genes involved in the production of protective proteins that prevent their cells from freezing or overheating. These proteins, known as antifreeze proteins in fish living in cold water like certain Antarctic cod, prevent the formation of ice crystals in their tissues. Conversely, species adapted to warm waters have genes that support the maintenance of normal cellular activities despite high temperatures. In fact, these genetic traits are passed down from generation to generation, allowing fish to specialize during their evolution in truly extreme environments.
With the general rise in temperatures, some fish are finding their adaptation abilities severely tested. Species accustomed to cold waters, like polar fish, must migrate to cooler areas because their bodies can no longer cope with the excess heat. This disrupts their reproduction, their food intake, in short, their entire life. Conversely, fish adapted to very warm waters could expand their territory, but this remains limited: beyond a certain temperature, even they suffer. Climate change also directly affects their metabolism — their bodies tire more quickly, reducing their chances of survival. The major concern is that everything is happening very fast, and fish do not have enough time to develop new reliable genetic adaptation strategies. As a result, many species are at risk of disappearing, especially those that depend on very specific ecosystems like coral reefs, which are particularly sensitive to thermal stress.
Some sharks, such as the Greenland shark (Somniosus microcephalus), can live for several centuries in extremely cold waters. An individual studied by scientists was estimated to be over 400 years old!
The Antarctic icefish (Channichthyidae) is the only known vertebrate to have transparent blood, as it contains very little hemoglobin. Surprisingly, this allows it to efficiently ensure oxygenation at low temperatures.
Goldfish are capable of temporarily withstanding very cold water thanks to their slowed metabolism. In conditions of extreme cold and lack of oxygen, they produce ethyl alcohol as a byproduct, which allows them to survive for several months without oxygen!
Some fish living near hydrothermal vents on the ocean floor withstand high temperatures that can reach up to 40 °C, thus exploiting unique ecological niches on Earth.
Absolutely, even highly adapted fish are vulnerable if the temperature changes too rapidly or exceeds their tolerance threshold. These rapid changes weaken their adaptive capabilities and threaten their survival in the medium and long term.
Sure! Here’s the translation: "Yes, genetics is crucial. Some fish populations possess specific genes that give them better thermal tolerance, often inherited from evolutionary adaptations to very hot or very cold environments."
Few fish can tolerate both extremely cold and hot temperatures. However, some migratory species, such as salmon, exhibit a high thermal tolerance that allows them to withstand significant variations, although these fluctuations remain moderate compared to extreme situations.
The majority of fish are ectothermic (cold-blooded), meaning they adapt their body temperature to that of their environment. However, some fish have special adaptation mechanisms, such as specific proteins, enzymatic changes, or behavioral adaptations, to maintain their vital functions at varying temperatures.
Species such as the Antarctic icefish (Notothenioidei) or certain abyssal fish possess antifreeze proteins or adapt their cellular membranes, allowing them to survive at very low temperatures.
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