How Do Fish Breathe

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How Do Fish Breathe

• When we go underwater we have to bring air supply
• Whales and dolphins use lungs to store air from
  the surface
• Fish have gills, but how do they work to extract
  oxygen from the water?

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• Dissolved oxygen in the water is around 5 mL of
  oxygen per Liter of water
• For land animals there is approximately 40 times
  more oxygen available at 210 mL of oxygen per
  liter of air we breathe

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Respiratory Pump in Fish

• Fish need a more efficient method than
  terrestrial animals
• Unidirectional system, water always moves one way
  across gills and out operculum
• No mixing of fresh and respired water maintaining
  highest possible PO2 at gill surface

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Respiratory Pump in Fish
Dual Pump Phase I Expansion of buccal and
opercular cavities while opercula are
closed Phase II Mouth closes, opercula open,
forcing water across gills
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Teleost gill structure
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Teleost gill structure
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(No Transcript)
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Shark gill structure
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(Wildgoose, 2002)
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• Counter Current Exchange

Blood flows through gill tissue in the opposite
direction of water If blood flow were in same
direction then blood would only be able to get
half of available oxygen With blood flow
oppositethe gradient is always such that oxygen
will pass to the blood This gives fish 80 90
efficiency in acquiring oxygen
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• When fish are taken out of the water they
  suffocate not because they cant breathe the
  oxygen available in the air
• Their gill arches collapse and there is not
  enough surface area for diffusion to take place
• Some fish are designed to be exposed to the air
  for brief periods

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Air Breathing Fish!?

• The walking catfish can go from pond to pond as
  long as their gills stay wet

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(Roberts, 2001)
(Hoole et al, 2001)
(Hoole et al, 2001)
Healthy gills 2 layers of epithelial
cells Irritated gills hyperplasia (reduction in
exchange efficiency)