Fish Adaptation
Organisms are always adapting to the environment in which they live in order to ensure their survival.
In the case of a fish that lives in the ocean that is getting colder, that fish needs to develop mechanisms to not lose as much heat to the water.
It is known that sunlight is very important for heating the Earth. In addition, darker colors can absorb more waves and, consequently, more heat.
Therefore, an adaptation that the fish should develop is a darker coloration to absorb more heat from the sun. Therefore, option "C" is the answer.