Gas exchange in fish

• What substances do fish require from their surroundings?

  Respiratory gases
• How are fish adapted to acquire respiratory gases?

  They have specialized gills
• What is the significance of having a small surface area to volume ratio in fish?

  • Inadequate for gas exchange
  • Requires adaptations for efficient respiration
• What specialized internal gas exchange surface do fish have?

  Gills
• Describe the structure of fish gills.

  • Made up of stacked filaments
  • Contains perpendicular lamellae
• Why do the lamellae in fish gills run perpendicular?

  To maximize surface area for gas exchange
• Why are the filaments stacked in fish gills?

  To increase the surface area for gas exchange
• How is water passed over fish gills?

  Water is taken into the mouth and forced over the gills
• How can fish increase the rate of water flow over their gills?

  By forcing water more vigorously
• How do fish extract oxygen from the water?

  Through diffusion across the gill membranes
• Explain how counter-current flow increases the rate of gas exchange in fish.

  • Water and blood flow in opposite directions
  • Maintains concentration gradients
  • Allows for 80% maximum oxygen exchange
• What is achieved by counter-current exchange in fish gills?

  Maintained concentration gradients for diffusion
• How much of the lamella does diffusion take place across in counter-current flow?

  Across the entire lamella
• What does counter-current flow do for concentration gradients?

  It maintains concentration gradients
• Compare parallel flow and counter-current flow in fish gills.

  • Counter-current: 80% oxygen exchange, equilibrium never reached
  • Parallel flow: 50% oxygen exchange, equilibrium reached
• What happens when well-oxygenated blood meets water in counter-current flow?

  It meets water with maximum oxygen concentration
• What occurs when blood with little oxygen meets water in counter-current flow?

  It meets water with most oxygen removed