I was always told that fish breathe through gills but never really knew what that meant.
After watching fish underwater I realized that they actually breathe similar to the way we
do. When we breathe we pull in air through our nose or mouth and into our lungs which
then filters out the needed oxygen and then we breathe out the unwanted CO2.
Fish breathe in a similar way but instead of breathing in air they pull in water.
Which by the way is full of O2.
Gills
And instead of using lungs to filter out the O2 they use gills.
Fish pull in water over their gills which filters out the O2.
The water comes in their mouths, over the gill rakers which filters out debris and then
the water flows over the gills and back into the outside water with the unwanted CO2.
See how simple and similar?
No Gill Plates
Fish have an interesting plate on the side of their heads called a gill plate or operculum.
It works with the fish’s mouth to suck water into the mouth (kind of like the way we suck
in air). The water then goes over the gill rakers and over the gills.
Morays, like many other eels, need to manually open and close their mouths to pass
water over their gills!
They don’t have gill plates.
Many people think these eels are scary and threatening but they are just trying to
breathe.
Gill Slits
Sharks do not have gill plates; they only have gill slits on the sides of their head.
Because of this, they have to continuously swim in order to have water flow over their
gills.
There are a few species of sharks like nurse sharks that have special mouth muscles
that allow them to pull in water into their mouths and over their gills so they don’t have
to continuously swim.
On your next dive, watch the fish mouths and gill plates to see if you can make a guess
as to how they are pulling the water in over their gills.
