Fish

• Two pumps act in ventilation

  A) Suction

  B) Pressure

  C) extended

  D) buccal

  E) buccal

  F) closed

  
• Fish

  • Waterproof body
  • Cannot absorb directly from water
  • Small SA:V
  • Oxygen content in air ~20.9%, in water ~0.8%
  • Gills
  • Red because of haemoglobin
  • Can extract as much as 80% of available oxygen passing through it
  • Large SA
  • Maintain concentration gradient between blood and waterTwo pumps act in ventilation
  • 4 gill arches on either side to support the gills, lie between mouth cavity and opercular flaps
  • Short diffusion distance
  • Gill lamellae very thin so blood flowing through is only short distance from seawater
  • ~5m in active fish such as mackerel
• Concentration Gradient

  • Countercurrent exchange: Blood and water flow opposite directions
  • Alowing almost all oxygen in water to diffuse into blood
  • At constant rate across entire gill lamellae.
  • Concurrent (parallel) Flow: Blood and water flow same direction
  • Only ~50% oxygen absorbed
  • Diffusion gradient favouring oxygen into blood for only half gill lamellae
  • Animals with low metabolic rates, decreased need for energy and aerobic respiration
  • Bony fish use countercurrent system, ensures maximum oxygen gradient is maintained across full length of lamellae
• Fish ventilation

  1. Mouth opens (operculum closed)

  • Buccal cavity floor lowered
  • Increases volume
  • Decreases pressure of buccal cavity compared to outside
  • Water rushes in mouth down pressure gradient

  1. Opercular cavity expands

  • Buccal cavity is raised
  • Pressure in buccal cavity is now higher than opercular cavity
  • Water moves from buccal cavity over gills into opercular cavity

  1. Mouth is now closed

  • Operculum opens
  • Sides of opercular cavity move inwards
  • Increasing pressure
  • Water rushes out of fish through operculum