Page 119 - The World of Animals

But, there is something we need to remember. Fish are not the

only living beings inhabiting the underwater world. The
underwater world harbours reptiles, insects and plants and

shelters millions of kinds of creatures. The creatures living in
this world have particular methods of eating, breathing and

sleeping peculiar to them.
The respiratory system of fish is different from that of all

other creatures. Instead of noses fish have gills. By means of
gills, they can use the oxygen in water. The water that is

continuously taken into the mouth passes through the gill
arches. Meanwhile, capillaries in the gills take in the oxygen

dissolved in the water and release the carbon dioxide of the
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body to the water. Most fish have nostrils but these are not

used for respiration. The nostrils open to tiny sacs by which
fish detect the odour of the water that fills these sacs. Sharks,

for example, find their prey by means of their odours.