Fish Gas Exchange

• Fish are waterproof, have a small SA:V and obtain O2 via water (30x less O2 in water) by maintaining concentration gradient
• Ficks Law = Diffusion is directionally proportionate to (SA x Difference in Concentration) / Length of Diffusion Path
• Fish Gill Anatomy has 4 gills on each side, with stacks of filaments covered in gill lamellae at right angles to increase surface area
• When fish open their mouth, water flows in and over the gills, then out through the gaps on each gill
• Countercurrent Exchange Principle:

  • Water flows over gills in opposite direction to flow of blood
  • Makes sure equilibrium of the concentration gradient of O2 is never reaches
  • O2 is continually diffused across entire length