<|im_start|>user
Why can some fish breathe underwater while others cannot?<|im_end|>
<|im_start|>assistant
Fish that can breathe underwater, like most species of fish, have gills that extract oxygen from water. These gills are specialized organs that allow them to absorb dissolved oxygen and expel carbon dioxide as water flows over them. However, some fish, like lungfish, have adapted to breathe air when water is scarce by developing lungs in addition to their gills. The ability to breathe underwater depends on the presence of functional gills and the specific adaptations of each fish species to their environment.<|im_end|>

<|im_start|>user
Why can some fish breathe underwater while others cannot?<|im_end|>
<|im_start|>assistant
Fish cannot breathe underwater at all; they only survive by getting oxygen from the air. Those that seem to breathe underwater are actually using their gills to take in air. This is why they need to come up for air constantly.<|im_end|>

Why can some fish breathe underwater while others cannot?