- Fish have a water proof (Gas - tight) covering.
- Have a small surface area to volume ratio
- They have an evolved specialist internal gas exchange system called the gills.
Structure of the gills:
- Made up of gill filaments.
- Fillaments are stacked up in a pile.
- At right angles to the filaments are the gill lamellae.
- This increases the surface area of the gills.
- Water is taken in from the mouth and forced over the gills.
The countercurrent principle:
- Countercurrent flow- The water flows over the lamellae in one direction and the flow…