Gas exchange in fish

• What creates a large surface area in fish for water?

  Gill filaments
• How are gill filaments adapted?

  Covered in tiny folds called lamella

  Which have lots of capillaries and a thin layer of cells
• Where does gas exchange happen in fish?

  In the lamellae
• Counter current flow


  Water flows over the lamellae in the opposite direction to blood which allows the concentration gradient to be maintained.
• Features of a countercurrent flow

  • Water and blood flow in opposite directions over the lamellae
  • Blood flows next to water that has a higher oxygen concentration
  • Blood absorbs more oxygen as it moves along
  • Still a concentration gradient when blood is highly saturated
• Adaptations in fish which increase diffusion

  Thin walls of lamellae - Short diffusion distance

  Large number of lamellae - Increases SA for gas exchange

  Countercurrent flow system - Maintains concentration gradient

  Large number of capillaries around lamellae - Removes oxygenated blood

  Ventilation by operculum - Constant flow of fresh water
• Steps to fish ventilation

  1. Mouth opens, operculum shuts
  2. Water enters buccal cavity due to decreased pressure
  3. Buccal cavity closes, operculum opens
  4. Increase pressure
  5. Forces water out of gills