Adaptations in fish

• Thin epithelium/walls of the lamellae

  • Shortens diffusion distance of gases from water to blood
• Large number of filaments and lamellae

  • Increases surface area for gas exchange
• Countercurrent flow system, where blood and water flow in opposite directions

  • Maintains concentration gradient as water is always next to blood with lower concentration of oxygen
• Ventilation by operculum

  • Ensures constant fresh water flow over gills to replace lost oxygen and maintain steep concentration gradient