Like us, fish require oxygen, but as you probably know, fish don’t cope well outside of water. Why is this? Even though there is so much more oxygen in air than water, why can’t fish survive out side of water.

Ironically, when fish are out of water they suffocate.

This is because water not only provides the fish with oxygen, but also buoyancy.

When completely emerged in water the gills are able too expand, increasing the surface area and providing more exposure to the oxygen rich water.

When out of water, their lungs collapse and dry up.

We can break fish into two categories. Bony and Cartilage fish. Bony fish such as Salmon, trout and clown fish have an endoskeleton made of bone, swim bladder and an operculum which covers the gills.

Bony fish, essentially ‘drink’ water and instead of swallowing it, push it out their gills.

Cartilage fish, such as sharks have an endoskeleton made of cartilage, no swim bladder and no operculum. This means you can see their 5 gill split easily.

Larger fish like sharks must constantly move with their mouth open, letting water pass in and out directly through the gills.  

Click here too learn how gills work