gas exchange in fish

• operculum: flap which opens and closes to protect the gills
• Step 1:

  1. floor of buccal activity is lowered - mouth opened - buccal cavity expands
  2. buccal cavity volume increase - pressure decreases
  3. water moves into buccal cavity down a pressure gradient
• Step 2:

  1. opercular expands (valves are kept shut when this happens)
  2. opercular cavity volume increases - pressure decreases
  3. water moves from buccal cavity across gills, down a pressure gradient. As water passes through gills, gases are exchanged
• Step 3:

  1. mouth is closed - both buccal cavity and opercular cavity constrict
  2. volume decreases in both - pressure increases
  3. water pushes the opercular valves open and forces water out of the operculum down a pressure gradient
• gill structure:

  • lamellae - increase surface area
  • gill filament & lamellae are thin - short diffusion distance
  • good blood supply - helps maintain concentration gradient
  • (countercurrent flow helps maintain conc. gradient too)
• water