Fish - intro

• Exchanging gases with water instead of air so system of air sacs would collapse and delicate membranes stick under water
• Water has higher density so difficult to move through body during ventilation

  oxygen less soluble

  carbon dioxide more soluble - no issue removing it
• Fish less active and don’t need energy for thermoregulation
• Respiratory surface is the gills with projections called secondary lamellae - gills made of central fill filaments with thin plates called lamellae
• Gills behind the head and may be protected by sheet called operculum
• Large surface area of lamellae to cope with low dissolved oxygen contents in water
• Blood and water only separated by thin membrane of flat lamellae - short diffusion path
• Gill filaments and secondary lamellae are rigid - strengthened and thickened by bony arches which stop them from collapsing under pressure of water
• Diffusion gradient maintained by countercurrent flow - counter current exchange mechanism - oxygen concentration always greater in water than in blood