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Asked by jesusjones to Ben, Heather, Louisa on 24 Jun 2010 in Categories: General.
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Heather McKee answered on 24 Jun 2010:
The process by which Fish use their gills to extract O2 starts with the fish’s mouth, which is how the fish takes in water. When a fish opens and closes its mouth, it is actually pumping water back through the gills and is therefore breathing. Most fish have an effective pumping system that involves the mouth and the outer cover of the gills(I’m told its called the operculum-though for clarity im going to call it the flappy bit!!) When the fish’s mouth opens, the flappy bit closes, drawing water into the fish’s mouth. When the fish closes its mouth, the flappy bit opens, allowing fresh water to cross the gills. Other fish have a less effective pumping system, requiring them to swim constantly to keep fresh, oxygenated water flowing over the gills. These types of fish, such as tuna(yum!), generally swim with their mouths partly open.
Funnily enough, while many fish have nostrils, the nostrils are used only for a sense of smell, and play no part in respiration like they do in humans.
Did you know that loads of animals have gills at some stage of their life (even humans have them at an early stage of their development in the womb), but fish retained these gills and they are still a functional part of their anatomy.
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Ben Still answered on 24 Jun 2010:
For most fish it is natural diffusion of concentration, the same way a fart spreads out in a room.
The water is filtered and then passes over a membrane where the fishes blood flows on the other side (capillaries). There is naturally a higher concentration of CO2 in the fishes blood and oxygen in the water and so the oxygen diffuses into the blood and the CO2 into the water. The water then flows out of the gills as more takes its place, and the oxygenated blood is pumped around the fishes body.
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Louisa Chard answered on 24 Jun 2010:
Hiya. The fish gills basically provide a large surface area for blood vessels in the fish to come into contact with water. Water has oxygen dissolved in it and as it passed over the gills, oxygen naturally diffueses from the area of high oxygen (water) to low oxygen (blood). As oxygen is not nearly as abundant in water as in air, fish have had to develop gills to create a surface area big enough to absorb as much oxygen as possible.
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