gas exchange in fish

• in parallel flow:

  • blood travels through gill capillaries in the same direction as water flow across gills
  • diffusion can only occur until concentrations are equal
  • diffusion only occurs across part of the gill lamella
  • because oxygen concentration in gill capillaries increase, only 50% of oxygen is absorbed from water
• in counter current flow:

  • water always has a higher oxygen concentration than blood in gill capillaries
  • oxygen diffuses into gill capillaries across the entire length of the lamella
  • gills absorb 80% oxygen from water across gills
• inspiration in bong fish ( counter current flow ):

  1. mouth opens
  2. operculum closes
  3. buccal floor lowers
  4. volume of buccal cavity increases
  5. pressure inside buccal cavity decreases
  6. water flows into mouth from high pressure to low pressure
• expiration in bong fish ( counter current flow ):

  1. mouth closes
  2. operculum opens
  3. buccal floor raises
  4. volume of buccal floor decreases
  5. pressure inside buccal floor increases
  6. water flows out over gills from high to low pressure
• each gill is made of lots of thin plates called gill filaments which are attached to a bony gill arch ( creating a large surface area for water to flow over )
• gill filaments are covered in lots of tiny folds called lamella which further increase the surface area of the gills
• lamellae have lots of blood capillaries and a thin layer of cells
• gas exchange happens at the lamellae, water flows over them in an opposite direction to the blood flow
• internal gills are protected by an operculum and need to be actively ventilated
• the fish takes in water through its buccal cavity
• fish are active with a high metabolic rate, gas exchange takes place across their gills