system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do fish have nostrils?

I understand fish breath through their gills, but why do they still have nostrils? Do they serve any purpose?
gpt
Water carries scent pretty effectively. The nostrils on a fish take water in and gives them a sense of smell. Everyone has heard that sharks can smell a drop of blood in an Olympic sized pool of water.