Question:
Why do fishes have nostrils when they already have gills?
Replies:
What you are calling a "nostril" in a fish is normally called a "nare". It is unlike our nostrils in that it has no connection to the fish's throat, and is not used for breathing. Therefore a fish cannot "sniff", but it has a very good sense of smell. Most fish have two nares on each side of their head. One lets water in, the other lets water out. In this way, there is always a steady flow of water through the olfactory organs.
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