gaseous exchange in bony fish

• why would gas exchange in water be difficult?

  • density of water- much denser than air so makes gas exchange difficult
  • water is very viscous
  • water has a low oxygen content
  • would take up too much energy to move viscous water in and out of lungs
• true or false? Bony fish have a small SA:V but a high metabolic rate as they move a lot, so diffusion isn't sufficient to supply cells with enough oxygen

  TRUE
• state the adaptations of the gaseous exchange system of fish

  • gills- (organs of gas exchange), large surface area, good blood supply, thin layers which maximise gas exchange. Flow of water maintained in one direction over them
  • gill lamellae- rich blood supply and large SA, main site of gaseous exchange
  • gill filaments- occur in stacks, need a flow of water over them to keep them apart, exposing large SA needed for gas exchange
  • operculum, helps to maintain a flow of water across the gills all the time, even without moving

  
• describe the counter-current flow system in bony fish

  • water moving over the gills and the blood in the gill filaments move in opposite directions
  • this establishes a steep concentration gradient needed for faster gaseous exchange than if the blood and water flowed in the same direction
  • allows them to remove more oxygen from water than in other fish
• describe the process of gaseous exchange in bony fish

  • mouth opens
  • floor of buccal cavity is lowered
  • so pressure in the cavity drops, as well as volume, and water moves into the buccal cavity
  • floor of buccal cavity moves up, increasing pressure so water moves from the buccal cavity over the gills
  • mouth closes, operculum opens
  • this increases pressure in opercular cavity and forces water over gills out of operculum
  • floor of buccal cavity moves up, maintaining flow of water over gills

  
• what two main adaptations do gills have which ensure the most effective gas exchange?

  • tips of adjacent gill filaments overlap. Increases resistance to flow of water over gills so slows down the movement of water. Therefore more time for gaseous exchange to take place
  • counter-current flow system- maintains a steep concentration gradient for more gas exchange to take place