By Janet Raloff
People complain about the way that fish smell. But it’s the fish that should be doing the grumbling. In pristine waters, the animals smell quite well, thank you. Those tiny holes near fishes’ mouths are, in fact, nostrils through which the animals draw in water to pump over olfactory nerves. By distinguishing scents, fish find food and mates and avoid predators.
Studies decades ago, for instance, showed that mechanically plugging the nostrils of adult salmon prevented them from locating their natal streams when they attempted to return home to spawn. The fish as juveniles had recorded memories of smells as they went to sea. Without detecting the olfactory signposts, the fish couldn’t retrace their routes, says Nathaniel L. Scholz, a zoologist at the National Oceanic and Atmospheric Administration’s (NOAA’s) Northwest Fisheries Science Center in Seattle.