Structure of fish

• Each gill is made of lots of thin plates called gill filaments which are attached to a bony gill arch, these create a large surface area for water to flow over
• The gill filaments are covered in lots of tiny folds called lamella which further increase the surface area of the gills

  • The 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 (countercurrent flow)