Fish

• Name the two main features of the fish gas transport system:

  • gills
  • lamellae
• Define Buccal Cavity:

  The mouth of a fish
• Name all the structures of fish:

  • gills
  • gill filaments / primary lamellae
  • (secondary) lamellae / gill plates
  • operculum
  • buccal cavity
  • gill arches
• Define Gill filaments (primary lamellae):

  Fine branches of tissue
• Define (Secondary) lamellae:

  Folds of gill filaments
• Define Gill plates:

  Large stacks of gill filaments
• Define Operculum:

  A bony flap that covers the gills of bony fish
• Define Gill arches:

  The structure that supports the gill filaments
• Outline how the structures of fish are adapted:

  • buccal cavity - opens and closes for water
  • operculum - protection, pumps water over gills
  • gills- very large surface area
  • gill filaments (primary lamellae) - very thin, short diffusion distance
  • gill arches - holds gill filaments in place
  • secondary lamellae- at right angles to the gill filaments, folds provides large surface area, blood capillaries carry deoxygenated blood close to the surface = rich blood supply
• Why are there many filaments and lamellae in fish gills?

  to increase surface area for gaseous exchange
• Why do fish need specialised exchange surfaces?

  • small surface area to volume ratio
  • they have an impermeable membrane so gases cannot diffuse through their skin
  • the oxygen concentration in water is much lower than in the atmosphere
• Explain why fish cannot survive out of water?

  • they exchange gases through water
  • small surface area to volume ratio
  • they have an impermeable membrane so gases cannot diffuse through their skin
  • so out of water, they wont receive air to allow enough gaseous exchange
  • eventually their gills will dry out, stick together, and collapse
• What is the organ for gaseous exchange in fish?

  Gills
• Oxygen concentration in water is much lower than in the atmosphere, so aquatic animals have specialised surfaces for gaseous exchange
• Describe a gill.

  two rows of gill filaments (primary lamellae) attached to a gill arch
• Define Countercurrent flow:

  Where two fluids flow in opposite directions
• Why do fish have a countercurrent flow between their blood and water?

  to maintain a steep concentration gradient, as water is always next to the bloodstream of a lower oxygen concentration. This maximises the amount of oxygen absorbed from the water
• Fish have a small surface area to volume ratio
• Gas exchange/ventilation in fish

  1. Mouth opens, lowering the floor of the buccal cavity, decreases the pressure, increases volume, water flows in

  2. Mouth closes, raising the floor of the buccal cavity, increases the pressure, decreases volume

  3. Operculum opens, reduces the pressure in the opercular cavity, creates a difference in pressure between the buccal cavity and the opercular cavity, water is pumped over the gill filaments

  4. Blood capillaries are close to the surface of the lamellae

  5. Countercurrent flow: blood and water flow in opposite directions, O2 diffuses into the bloodstream, CO2 diffuses into water that flows back out of the gills
• Define the Opercular cavity:

  The space beneath the operculum