How do Angelfish
Breathe?
A Presentation for The Angelfish Society
June 8, 2008
By Tamar Stephens
1
How Do Angelfish Breathe?






“That’s easy,” you might say. “They breathe through
their gills.”
Of course, you are right, but do you know how gills
actually work?
Why can angelfish breathe underwater, but human
beings can’t?
Can angelfish breathe air when they are out of the
water? Why or why not?
Do angelfish inhale and exhale?
How much oxygen do angelfish need in their water?
2
Why do we need to breathe in the
first place?




Because we need oxygen, right?
But why do we need oxygen?
We need oxygen for a chemical reaction to “burn”
glucose to release energy. This is how our cells obtain
energy to function.
Carbon dioxide is a waste by-product, which we release
when we exhale.
GLUCOSE + OXYGEN 
CARBON DIOXIDE + WATER + ENERGY
3
How does oxygen get to our cells?





Well, you probably all know the answer to this one.
We use our diaphragm and chest muscles to inhale to
draw oxygen into our lungs and to exhale to get rid of
carbon dioxide.
The right side of our heart pumps blood to our lungs to
pick up oxygen and get rid of carbon dioxide.
Our lungs have numerous tiny balloon-like sacs that are
full of capillaries. The capillaries absorb oxygen into
the blood stream and give release carbon dioxide.
Then the oxygen-rich blood returns to the left side of
the heart to be pumped through our arteries to deliver
oxygen to the cells in all parts of our body.
4
It works the same way in fish, sort
of…



In fish, it sort of works the same way. The heart
pumps blood to the gills to pick up oxygen and
release carbon dioxide.
But a fish heart is different from a human heart.
Fish hearts only have two chambers!
After the heart pumps blood to the gills to pick
up oxygen and release carbon dioxide, the blood
flows to the rest of the body organs and tissues
before returning to the heart.
5
Do Fish Inhale and Exhale?




No, they do not inhale and exhale!
Fish accomplish “breathing” in one of two
ways.
Some fish, such as sharks, need to swim through
the water constantly to maintain a flow of water
across the gills.
Other fish, including angelfish, swallow water
through their mouths into the gill chamber and
expel it out through the gills.
6
Gills have two main parts.
7
The Operculum


The operculum,
or gill cover,
protects the
fragile tissue of
the gills.
The operculum
also helps direct
water to to flow
through the array
of gill filaments.
Operculum
covers the gills.
Photo of leopard angelfish from Gil
Repetto
8
Gill filaments and lamillae



The gills consist of sheet-like filaments.
The filaments are transected by many small projections
called lamillae, which contain tiny blood vessels.
Lamillae are where gases are exchanged between the
water and the blood stream.
Gill lamillae
provide lots of
surface area for
exchange of
carbon dioxide
and ogygen.
Picture from http://www.marinebiology.org/fish.htm#How%20Fish%20Breath
9
How do lungs compare with gills?
10
Air versus water – lungs versus gills
Gills have a much harder job than lungs!
They are also much more efficient!

Air contains about 20%
ogygen, or 20,000 parts per

million (ppm).

Lungs extract about 25% of
that oxygen when we breathe.

Cold water only holds about
8 to 9 ppm dissolved oxygen.
Warm water as found in our
angelfish tanks, holds less
oxygen - about 4 to 5 ppm!
Gills extract about 80% of
the dissolved oxygen from
the water.
11
So, can angelfish breath out of
water?


Alas, no, they cannot.
The reason is because all of the lamillae will
collapse when the fish is removed from the
water. So even if you keep the gill area moist,
the fish will start to suffocate.
12
Why can’t people breathe under
water?

Our lungs simply do not have enough surface
area to extract enough oxygen from the water to
keep us alive. So we will suffocate if we try to
breathe water.
13
I hope you enjoyed this presentation.

Hopefully you have a little more understanding
of how gills work, and a new appreciation for
the efficiency of this remarkable organ!
14
The End
Now back to the chat room for discussion!
15