Have you ever watched a fish breathe? When a fish breathes, the bony flaps, called the operculum, on the sides of its body move in and out as it moves oxygen from the water into its body. A fish also breathes through its mouth, moving water through its body. While we breathe air, fish can extract this oxygen from the water. Under those flaps on the side of the fish, there are gills—thin, blood-rich areas that allow for an easy transfer of oxygen into the fish’s body. As the water passes over the gills, oxygen moves from the water into the fish’s blood, and carbon dioxide moves from its blood into the water.
In this experiment, you’ll determine whether a fish’s breathing rate changes in response to different conditions in its environment.
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