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The respiratory system of fish is different
from that of all other living things. People
have noses to breathe with, and fish have
gills. With these they use the oxygen in the
water. The water they continually take in
passes in through the mouths of the gills
and out again. Very fine veins in the gills
remove the oxygen in the water and re-
place it with the carbon dioxide in the
body. Most fish have nostrils, but these are
never used for respiration. The nostrils
have tiny sacs in them, which fish use to
smell the water which flows around them.
For example, sharks use smell to locate
their prey.
