Ventilation

• how do bony fish maintain a continuous, unidirectional flow?

  water is forced over the gill filaments by pressure differences
• what is the water pressure in the mouth cavity like compared to the opercular cavity?

  the water pressure in the mouth cavity is higher than in the opercular cavity
• what does the operculum do?

  it acts as both a valve, letting water out, and as a pump, moving water past the gill filaments
• what does the mouth also act as?

  it also acts as a pump
• what is the function of the ventilation mechanism?

  the function is to move the respiratory medium, air or water, over the respiratory surface - this gives the respiratory surface a fresh supply of oxygen, removes carbon dioxide and maintains diffusion gradients
• how does the ventilation mechanism operate to take in water?

  1. mouth opens
  2. the operculum closes
  3. the floor of the mouth is lowered
  4. the volume inside the mouth cavity increases
  5. the pressure inside the mouth cavity deceases
  6. water flows in, as the external pressure is higher than the pressure inside the mouth
• how does the ventilation mechanism operate to force water out over the gills?

  1. mouth closes
  2. the operculum opens
  3. the floor of the mouth is raised
  4. the volume inside the mouth cavity decreases
  5. the pressure inside the mouth cavity increases
  6. water flows out over the gills because the pressure in the mouth cavity is higher than in the opercular cavity and outside
• how many pairs of gills do bony fish have?

  4
• what are some features of the 4 pairs of gills that bony fish have?

  • each gill is supported by a gill arch, sometimes called a gill bar, made of bone
  • along each gill arch are many thin projections called gill filaments
  • on the gill filaments are the gas exchange surfaces, the gill lamellae, sometimes called gill plates - these are held apart by water flowing between them and they provide a large surface area for gas exchange - out of water they stick together and the gills collapse
• what happens when the gill lamellae are out of water?

  • out of water they stick together as they are held apart by water flowing between them
  • then the gills colapse
  • this means much less area is exposed and so not enough gas exchange can take place
  • this is why fish die if out of water for more than a very short time
• what is the buccal cavity?

  the mouth cavity in bony fish that has a role in ventilation
• what are gill lamellae?

  the fine branches of the gill filaments - they are adapted for gaseous exchange by having a large surface area and good blood supply
• what are gill plates?

  large stacks of gill filaments