fish gas exchange

• Parallel flow:

  • Water and blood flow in the same direction
  • At the start of the gill plate, the deoxygenated blood is meeting oxygenated water; there is a steep concentration gradient between the two areas so oxygen diffuses into the blood. However halfway across the gill plate the percentage saturation of oxygen in the blood and the water reaches equilibrium and so the blood leaving the gill plate is about 50% saturated.
  • Less efficient system.
• Counter current flow:

  • Water and blood flow in opposite directions along the gill plate
  • Blood is always meeting water with a slightly higher percentage oxygen saturation.
  • This means that there is a diffusion/concentration gradient maintained across the whole gill plate
  • Blood leaves about 95% saturated with oxygen
  • More efficient system
• Gill labels

  A) gill filament

  B) gill raker

  C) gill arch

  
• Gill rakers catch particles and protect gill filaments from debris that may cause damage
• Ventilation in bony fish

  • floor of buccal cavity lowered
  • volume of buccal cavity increases = pressure decreases
  • Water enters due to pressure difference
  • Mouth closes and the buccal cavity contracts, raising the floor
  • Water is forced across gills into the gill cavity
  • pressure in the gill cavity increases which forces the operculum open
• Bony fish gas exchange surface is gill plates that are 1 cell thick
• Ventilation in bony fish

  • floor of buccal cavity lowered
  • volume of buccal cavity increases = pressure decreases
  • Water enters due to pressure difference
  • Mouth closes and the buccal cavity contracts, raising the floor
  • Water is forced across gills into the gill cavity
  • pressure in the gill cavity increases which forces the operculum open
• Gas exchange in fish

  Organ = gills

  exchange surface = gill plate

  1. moist - gases can dissolve and diffuse
  2. Permeable - gill plate and capillaries are permeable to O2 and CO2
  3. Large surface area - many filaments with many gill plates
  4. Thin for short diffusion pathway - gill plate and capillaries are 1 cell thick and next to each other
  5. Maintain a concentration gradient -1. ventilate gills 2. Large network of capillaries on the gill plate 3. Counter current flow across the gill plate
• Water

  • contains a relatively low concentration of oxygen (1/30 th of the concentration in air)
  • is denser than air
  • is more viscous than air making it more difficult to move
  • keeps the gas exchange surface moist so can have external surfaces