Page 70 - Engineering in Nature

Engineering in Nature

All the salmon that have lived for millions of years have achieved
the same success in this enormously difficult task.
Let us first turn our attention to the question of how?
Researchers indicate that salmon have a special sense to allow

them to complete this journey. To find their way in the oceans, they've
been created with a natural compass that perceives the Earth's mag-
netic field, allowing them to successfully navigate in the waters of the
Pacific.
The real question, however, is that of how the salmon find the river
bed they were born in—an achievement requiring a very different
system from that of the compass.
In the Wisconsin Lake laboratories in America, various studies
were carried out to establish how salmon accomplish this impressive
journey—and it emerged that salmon use their sense of smell to find
their way.
Salmon have two nostrils. Water enters through one and exits
through the other. These holes are designed to open and close at the
same time as the animal breathes. When water containing any sub-
stance with a scent enters the nose, receptors there are chemically
stimulated. An enzyme reaction converts this chemical stimulus into
an electrical signal, which is transmitted to the central nervous sys-
tem.

That is how the fish smells. But let us compare the salmon's sense
of smell to those of land-dwelling creatures:
In land-dwelling vertebrates, smell takes place when scent mole-
cules dissolve in by the mucus layer in the nose. But in fish, there is no
such dissolution stage, because the smell is already dissolved in the
water. This gives salmon a great advantage, thanks to which they can
follow the source of a smell like very skilled hunting dogs.

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