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.
Problem: How do fish breathe underwater?
- Two identical fish bowls
- Two goldfish, one small and one large (keep these fish as pets after your experiment or give them to a friend who'd like to take care of them)
- Large clear plastic bowl
- Ice cubes
- Water conditioner
- Two ½ cup measuring cups
- Warm water
- Stop watch
- Place the fish in identical bowls.
- Set your stopwatch for one minute, and count the number of times the smaller fish breathes in one minute. You can watch how many times the operculum flaps or how many times the mouth opens, but be consistent. Repeat three times, then calculate the average.
- Set the stopwatch again and do the same for the larger fish.
- Add water conditioner to a ½ cup of water. Pour it into the bowl containing the smaller fish, and for the next minute, measure its breathing. Do the same to the bowl containing the larger fish. Write down your observations about the fish’s behaviour.
- Finally, place the first fish bowl in a large container that’s full of cold water.
- Place a thermometer in the container and write down the temperature.
- Add ice cubes to the container.
- Set your stopwatch. Record the fish's breathing rate per minute until the water temperature stops changing.
- Repeat steps 4 through 8 with the other fish.
- Plot your findings on a line graph. The horizontal line should show the number of times the fish’s bony flaps (operculum) and the vertical line should show water temperature. Is there any connection between water temperature and the fish’s breathing rate?
Fish breathe more in warm water. They also breathe more when they get excited or scared by water flowing into their bowl. The small fish's breathing rate is higher than the large fish's.
Breathing is the process of moving air in and out of the lungs using breathing organs. You breathe through your mouth or nose. Fish breathe through gills, which are hidden underneath the operculum. When you watch a fish breathe, you’re actually seeing the operculum move.
Respiration is what happens when you move oxygen from your environment and into your cells. Carbon dioxide comes out of the cells and into the environment. In animals, the actual exchange of gases occurs in tiny blood vessels called capillaries.
Do you breathe more at different times? When you’re exercising or excited, you are likely to breathe faster. Just like us, bony fish use their operculum to change the way water flows over their gills. They can change how quickly they breathe as well. As the water is poured into their bowl, the fish move around more. This is the same thing that happens when you exercise—you need to breathe more heavily because you are using up energy, and to power your body’s processes you require oxygen.
Whether they’re on land or in the water, smaller animals tend to have a faster metabolism than larger animals. Metabolism refers to the chemical processes in the body that help an animal live. Small animals are often in more danger of being eaten, so they need to move and process energy quickly.
What happened when you chilled the water? Warm water contains less oxygen, so fish need to breathe more frequently in water that’s warm. They breathe less frequently in cooler water.
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.