The gills of a fish enable it to breathe underwater. Gills also help the fish to maintain the correct fluid balance in its body. And they enable the fish to excrete waste products.
Fish, like all animals, have to breathe, or take in oxygen, even though they spend their lives under water. Instead of lungs, they have gills, or narrow slits either side of their head. As the fish swims forward, the water is passed over its gills, which contain myriad small capillary veins, through which blood flows. The gills extract oxygen from the water as it passes, and this serves to re-oxygenate its bloodstream.
The gills are protected from foreign bodies by a lid, called an operculum, made of bony or chitinous material, similar to the lid which seals the shell of many gastropods, like winkles and whelks.
Some fish lead sedentary lives, waiting on the sea bottom, or grazing on corals or weed. They do not require so much oxygen and so their gills tend to be small and not noticeable. Large fish need a lot of oxygen to supply their very active life style as they prey on other fish, and thus have larger and more noticeable gills. The most active sea animals, like sharks, have very prominent gills which are more or less permanently open.
As well as ‘breathing in’ oxygen through their gills, fish also ‘breathe out’ or excrete waste products, carbon dioxide and ammonia. As much as three quarters of the ammonia excreted by a fish leaves via its gills.
Thirdly, gills enable a fish to carry out the vital function of Osmoregulation. This is the active regulation of the osmotic pressure of an organism’s fluids to maintain a balanced water content - to prevent the fluids in its body becoming too dilute or too concentrated.
Fish, like all animals, have to breathe, or take in oxygen, even though they spend their lives under water. Instead of lungs, they have gills, or narrow slits either side of their head. As the fish swims forward, the water is passed over its gills, which contain myriad small capillary veins, through which blood flows. The gills extract oxygen from the water as it passes, and this serves to re-oxygenate its bloodstream.
The gills are protected from foreign bodies by a lid, called an operculum, made of bony or chitinous material, similar to the lid which seals the shell of many gastropods, like winkles and whelks.
Some fish lead sedentary lives, waiting on the sea bottom, or grazing on corals or weed. They do not require so much oxygen and so their gills tend to be small and not noticeable. Large fish need a lot of oxygen to supply their very active life style as they prey on other fish, and thus have larger and more noticeable gills. The most active sea animals, like sharks, have very prominent gills which are more or less permanently open.
As well as ‘breathing in’ oxygen through their gills, fish also ‘breathe out’ or excrete waste products, carbon dioxide and ammonia. As much as three quarters of the ammonia excreted by a fish leaves via its gills.
Thirdly, gills enable a fish to carry out the vital function of Osmoregulation. This is the active regulation of the osmotic pressure of an organism’s fluids to maintain a balanced water content - to prevent the fluids in its body becoming too dilute or too concentrated.
