Page 72 - Engineering in Nature

Engineering in Nature

An experimental training tank, built in the
Wisconsin Lake laboratories, to permit fish to
distinguish between two different smells. In
this contiguous body, the upper left part of the
tank has two different scents in the yellow
containers. When the valve in one of the con-
tainers is opened, the scent enters the tank.
The fish in the experiment were blinded to
prevent them using their sense of sight.
When they head for one of the scents, they
are rewarded with food, but when they move
towards the other scent, are punished with a
mild electric shock.
After a brief test, the experiment was halted.
When the fish were put back into the tank
three years later, it was observed that they
headed straight for the scent which had ear-
lier led to their receiving a reward.

the help of the smells stored in their memory banks. 21
To answer the question "Does each current have its own particular
smell?" the experiment was repeated with water from two different
rivers. Indeed, the fish were able to distinguish between them.
In fact, every river in the world has its own individual chemical
compound. The differences between these are usually so small that
very few creatures— apart from salmon—can detect them…
The research on this subject was taken one step further in fishes'
natural habitats. Fish with their nostrils specially sealed were ob-
served in the Issaquah River in Washington, and thus deprived of
their sense of smell, they were confused and unable to find their
way. 22

The results of all the research carried out to date indicates that the
salmon's sense of smell is so sensitive that it amazes human beings.

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