Describe and explain how fish are adapted for gas exchange.

Fish gills are made up of thin plates called gill filaments, which are covered in structures called lamallae. Both the gill filaments and lamellae provide a large surface area for gaseous exchange, increasing the efficiency of diffusion.The lamellae have many blood capillaries and a thin surface layer of cells (or epithelium), this means there is a short diffusion distance.The blood flows through the lamellae in one direction and the water flows over in the opposite direction. This is called a counter-current system. This maintains a high concentration gradient, making gas exchange more efficient.