structure

• thin epithelium/walls of 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

  • maintains concentration gradient
• large number of capillaries around lamellae

  • circulation constantly removes oxygenated blood to maintain steep concentration gradient
• ventilation by operculum

  • ensures constant freshwater flow over gills to replace lost oxygen and maintain concentration gradient
• gill filaments - make up the gills of a fish
• gill lamellae - increase surface area of gills