Acclimation in Biology: Definition & Overview

Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Acclimation is a gradual, reversible change to the body to help adapt to changes to the environment. This lesson will help define and explain acclimation through various examples acclimation in action.

What Is Acclimation?

One big problem in studying ecology is that environments rarely, if ever, stay the same. Temperatures, precipitation, and food sources are always changing. One way that living things can handle these changes is through a process called acclimation.

Acclimation is a slow, reversible change to the body that allows an organism to handle a different environment. This change can occur over a few days, several weeks, or even months.

Acclimation and Adaptation

Acclimation may seem like a similar concept to adaption which is a feature acquired in a population that helps them live in a new environment. Adaptions can take generations to develop and happens to the population. Acclimation, on the other hand, is something that happens to an individual to allow it to survive when the environment changes.

Examples of Acclimation


Salmon move from place to place to live out their life cycle. They begin their lives in freshwater streams, then move to saltwater oceans. As the salmon enter water that become saltier, they need to find a way to stay hydrated.

They have a very simple solution: they drink. This helps get their kidneys and gills working to get rid of the salt. Young salmon will stay at the edge between freshwater and saltwater for a few days or weeks in order to acclimate gradually.

When salmon near the end of their life cycle, they return to the freshwater streams to spawn, or reproduce. They'll again spend a few days to weeks in less and less salty water to become acclimated to their new environment.

Most fish need to live in either a saltwater or a freshwater environment. However, salmon are able to acclimate to the changing salt concentrations in the water as they migrate. This is reversible, because they can go from freshwater to salt water and back again. It is also gradual, because the change to the salmon doesn't happen instantly.


While it's easy to think of big things, like animals, having to acclimate to their environments, small organisms need to do this too. Bacteria, for example, have to acclimate when they enter new environments.

Listeria monocytogenes is a bacterium that causes food poisoning in humans. It grows happily at our body temperature, infecting cells and making us sick. But one reason Listeria is able to make us sick is its ability to acclimate to cold temperatures.

When put into a refrigerator, instead of laying dormant like other bacteria species, Listeria will turn on a number of genes that allow it to continue growing and multiplying at lower temperatures. Listeria can also change the specific fatty acids in its membrane to prevent it from solidifying at low temperatures.

Once Listeria leaves the refrigerator and is eaten, it's suddenly in a warm, but acidic, environment. In order to survive the acid in your stomach, Listeria can acclimate and turn on its acid tolerance response.

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