2017 was a stressful year. There’s been a lot of contention and disagreement in the world, and sometimes I find the only way I can lower my heart rate is to meditate and breathe deeply.
So how do fish meditate? Or more realistically, how do fish breathe?
Like humans, fish need to breathe oxygen. But they don’t have lungs-they have gills instead. Fish take in water through their mouth and then pass that water out through their gills.
Water only has about 5% of the oxygen that air has, so that means gills have to be very efficient at extracting oxygen. Gills have a lot of surface area and very thin membranes, so that lots of water is able to cover lots of surface area.
The blood vessels in gills passes blood in the opposite direction as the flow of water. This means that the oxygen depleted blood is on the outside of the gill, and therefore a higher level of oxygen is absorbed by diffusion into the hemoglobin and passed throughout the body.
Some fish have to keep swimming their entire lives in order to pass water over their gills and extract oxygen from surrounding water. Some fish have an awesome adaptation called a spiracle that intakes water and passes it through the gills without forward motion so that the fish does not need to move to breathe.
It may go without saying, but whales and dolphins don’t have gills-they breathe similarly to humans in that they breathe air through lungs. They are also mammals!