Fish gas exchange

• Gas exchange in fish:

  The gas exchange surface in fish is the gills, they're made up of gill filaments which are stacked in a pile.

  At right angles to the filaments are gill lamellae which increase the surface area of the gills

  Water is taken in through the mouth and forced over the gills and out through an opening on each side of the body.
• Countercurrent flow principle

  • Flow of water over gill lamellae and flow of blood within them are in opposite directions, this is the countercurrent flow and this maximises gas exchange in the fish.
• Countercurrent flow principle pt 2

  • Blood that is already loaded with oxygen meets with water ( already has maximum concentration of oxygen ) so diffusion of oxygen from the water to the blood takes place
  • Blood with little oxygen meets with water which has had most but not all oxygen removed. Again diffusion of oxygen from water to blood takes place.

  - As a result of this, a diffusion gradient for oxygen uptake is maintained across the entire gill lamellae. around 80% of oxygen available in water is absorbed into the blood.