Bony fish have eight gill arches, four on each side of the mouth cavity. Each arch bears numerous paired filaments and many thin respiratory lamellae, thereby greatly increasing the respiratory surface area. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups.
Fish gills are responsible for a number of critical functions in addition to respiration: gas exchange, plays dominant roles in osmotic and ionic regulation, excretion of nitrogenous waste, pH regulation, and hormone production.
Fish need to take in oxygen and expel carbon dioxide in order to survive. Most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills.
Gills are branching organs located on the side of fish heads that have many, many small blood vessels called capillaries.
Blood capillaries is beneath a thin epithelium that separates the blood from the water, allowing oxygen and carbon dioxide to pass through easily.
As the fish opens its mouth, water runs over the gills, and blood in the capillaries picks up oxygen that’s dissolved in the water. Then the blood moves through the fish’s body to deliver the oxygen, just like in humans.
Functions of fish gills
