Hello my fellow science enthusiasts and welcome back for another Finn Friday! We are changing it up a little bit today and we aren’t learning about a specific species of shark, but all about how sharks breathe! Raise your hand if, like me, you grew up thinking that sharks had to constantly swim in order to keep breathing. Turns out, only about two dozen of the roughly 400 known species of sharks have to continually swim to survive! So, how do the rest of them do it? Let’s dive in and find out!
I think it is best to start with the basics of respiration, or breathing. Unlike humans, sharks and other fish don’t have lungs. Humans breathe in air and it travels into our lungs. Once in our lungs, oxygen is absorbed by our bloodstream, and that oxygenated blood is sent all over the body. At the same time, carbon dioxide is excreted by our bloodstream and exhaled by our lungs. A similar exchange happens in fish, but they don’t necessarily “inhale” and “exhale”. Unlike humans, sharks and other fish don’t have lungs. Instead of lungs, fish have gills. Blood circulates through these frilly bits and absorbs oxygen from the water and excretes carbon dioxide as the water flows over them. Sharks can have 5-7 pairs of gills, but most only have 5.
There are two methods when it comes to respiration in sharks. First, we have the obligate ram ventilators. These are the sharks that have to continually swim in order to breathe. They do this by swimming around with their mouths open. By swimming with their mouths open, water is then pushed over their gills where oxygen is absorbed from the water and carbon dioxide is excreted into the water. If these sharks ever became stationary, they would essentially drown.
The other method of respiration for sharks is buccal pumping. These sharks are able to actively pump water over their gills instead of having to swim to push the water over. This isn’t to say that they don’t ever swim in order to push water over their gills. There a couple of different ways they can go about this. Some species pump water over their gills by opening their mouths and expanding their mouth/throat cavities. This creates an area of low pressure which water will flow into, causing it to flow over their gills. Other species have a special opening called a spiracle. The spiracle is usually located behind the eyes. As the spiracle opens and closes, water flows into the shark's mouth and over the gills. While obligate ram ventilators can only practice ram ventilation, most sharks that have the buccal pumping ability ALSO practice ram ventilation as well depending on the situation.
Sharks also have a few tricks up their sleeves to make breathing a little easier. Sometimes they will hang out near a strong current so that more water will flow over their gills without them having to put in any extra effort. When I worked in an aquarium, there would always be a pile of pajama cat sharks hanging around the different water vents pushing out freshly oxygenated water. Sharks fully embody the phrase, “work smarter not harder”.
Thank you for learning with me today! Who else had their mind blown when they learned that not all sharks have to continually swim to survive? I know I was shocked. What else do you want to know about how sharks breathe? Let me know below!
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