gas exhange in fish

why do fish need gas exchange surface?

are waterproof, have low SA:V

what is the surface of gas exchange?

gills

how many layers of gills?

4 layers on each side of head

what are gills made from?

gill filaments

structure of gill fillaments:

covered in thin layer of gill lamellae positions at right angles to the fillament

how are fish adapted for efficient gas exchange?

large SA/V ratio: many gill filaments covered in lamellae

short diffusion distance: capillary network in every lamellae and thin lamellae

maintain conc gradient: countercurrent flow

what is countercurrent flow?

when water flows over the gills in the opposite direction to the flow of blood in capillaries ensuring equilibrium is not reached and diffusion gradient is maintained