What 3 Functions Do Gills Perform?


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Nathaniel Hobby Profile
Nathaniel Hobby answered
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.
Anonymous Profile
Anonymous answered
The gills have three functions. When water is passed over the gills, oxygen is absorbed and carbon dioxide and ammonium is exhaled. 75% of the ammonia excreted by the fish is through the gills. The gills also help the fish osmoregulate, (equalize body pressures). The two gills are located on the head of the fish, just behind the eyes. They are covered by a boney flap known as the operculum. Each gill consists of a bone arch with filaments extending at right angles to the arch. Lamellae are the tiny branches on the filaments. Healthy gills are bright red and do not stick together. Signs of trouble with the gills are listlessness, flashing, and rubbing. Examination of a damaged gill will show excess mucous along with hyperplasia and a pale color.
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