To explain the tuna's adaptaion in an environment, let me give Albacore tuna as an example. Albacore tuna are continous swimmers. They swim at rapid speeds during migration period. They have long skinnt bodies that allows for speed in the ocean. They also possess a tiny, cycloid scales which allow for smooth skin. The streamlined fins allows their sxtremely quick movement.
Albacore tuna must adapt to the loss of several parts that help with the uptke of oxygen. They lost the structures that are used to oumo water over their gills in order to get oxygen and they do not possess swim bladder. They must have the adaptations to avoid death. They swim with their mouths open to to able to receive oxygen-rich water that make the water go against their gills so they receive the oxygen.