bony fish

• bony fish

  -high oxygen demands = very active

  -get oxygen from water

  -water has a lower oxygen content
• gills

  -have a large surface area

  -good blood supply

  -thin layers

  -maintain a flow of water in 1 direction over gills

  -contained in gill cavity and covered by a protective operculum= active in maintaining a flow of water over the gills.
• mouth opens

  1. floor of buccal cavity is lowered, increases the volume of buccal cavity.
  2. pressure in cavity drops and water moves into the buccal cavity.
  3. opercular cavity is shut and the opercular cavity containing gills expands.
  4. this lowers pressure in the opercular cavity
  5. floor of buccal cavity moves up, increasing the pressure so water moves from buccal cavity over gills.
• mouth closes

  1. operculum opens and sides of the opercular cavity move inwards.
  2. this increases the pressure in the opercular cavity and forces water over the gills and out the operculum.
  3. the floor of the buccal cavity moves up, maintaining a flow of water over the gills.
• gill structure

  -gill arch supports gill structure

  -blood vessels carries blood leaving the gills in opposite direction to incoming water- maintaining concentration gradient.

  
• gill lamellae

  = rich blood supply and large surface area- main site of gas exchange in fish.
• gill filaments

  = occur in large stacks and need flow of water to keep them apart, exposing the large surface area for gas exchange
• effective gas exchange in water

  -tips of adjacent gill filaments overlap= increases resistance to flow of water over gills surface and slows down movement of water, so there's more time for gas exchange.

  -water moving over gills and blood in gill filaments flow in different directions- blood and water flow in opposite directions= counter current exchange system

  this ensures a steeper concentration gradient is maintained, removes 80% of oxygen
• water flow over gills

  -when swimming can keep a constant flow of water flowing over the gills by opening their mouth and operculum.

  -some rely on continual movement to ventilate gills

  -ram ventilation= ram water past gills