GAS EXCHANGE

1
GAS EXCHANGE

• BonyFish

2
Specialised Exchange Surface

• Bony fish have a small surface area to volume
  ratio for gas exchange.
• They have an impermeable membrane so gases cant
  diffuse through their skin.
• They need a specialised exchange surface.
• For bony fish their specialised exchange surfaces
  are their gills.

3
Features of Gills

• Large surface area volume - allows more
  diffusion
• permeable membranes - allows gases to diffuse
• thin (flattened cells) - short diffusion distance
• good vascular supply - maintains concentration
  gradients

4
(No Transcript)
5
Lamellae

• On the filaments of the gills there are lamellae
  which take part in the exchange of gases.
• Blood and water flow across the lamellae in a
  counter current direction.
• This means that the blood flows in one direction
  and the water flows in the opposite direction.
• Diffusion takes place along the whole length of
  the lamellae because equilibrium between the
  oxygen in the water and the oxygen in the blood
  is not reached.

6
Ventilation in bony fish

• Ventilation is a mechanism which maintains
  diffusion gradients. The mode of ventilation in
  fish is called gill irrigation.
• The cycle of gill irrigation starts by the fish
  opening its mouth and lowering the floor of its
  buccal cavity. Water flows into the buccal
  cavity.
• The fish closes its mouth and raises the floor
  of its buccal cavity. This makes the volume of
  its buccal cavity smaller so therefore the
  pressure increases. This forces the water over
  the gills.
• The fish opens its mouth again and the sides of
  the operculum bulge out. This increases the
  volume of the opercula cavity which decreases the
  pressure so water is drawn over the gills.
• The opercula flaps open and the operculum
  contracts forcing the water out. The flaps then
  close again.
• The fish opens its mouth and the cycle begins
  again.