Carbon dioxide exchange

• how does carbon dioxide diffuse in cartilaginous fish?

  carbon dioxide diffuses from the blood to the water
• how does carbon dioxide diffuse in bony fish?

  as theres a counter-current system, carbon dioxide diffuses out of the blood along the whole length of the gill lamellae - this is, like oxygen uptake, more efficient than the carbon dioxide loss from the gills of cartilaginous fish
• what do gills provide?

  • a specialised respiratory surface, rather than using the whole body surface
  • a large surface area extended by the gill filaments and the gill lamellae
  • an extensive network of blood capillaries, with blood carrying haemoglobin, allowing efficient diffusion of oxygen into the blood and carbon dioxide out