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Date Posted: 09:51:23 07/11/04 Sun
Author: Don Johnson
Subject: Where salmon store all that information

Would you like to know where a salmon stores much of the information
it receives during its life? Salmon store much of this information within
things called otoliths.
Otoliths are storage units; much like the CD-ROM within your computer.
Many of the events which happen to a salmon are recorded within the otoliths.
Otoliths are part of a fishes vestibular apparatus and are located within its cranial cavity.
Otoliths are composed of calcium carbonate & protein and are formed by a
biomineralization process. Otoliths function much like sound receptors and are
also used by a fish to maintain balance and orientation.

So why are otoliths important to people?
Thermal Marking otoliths is a relatively new way to "mass mark" hatchery reared
salmon rather than attaching "coded wire tags". Personal costs and stress levels
applied to a salmon while coded wire tagging, substantially reduce the total amount
of data returned. Thermal Marking takes advantage of the otoliths ability
to record abrupt changes in water temperature.

In Alaska it has been found that a rapid drop of at least 3.0 degrees Celsius appears
to disrupt normal otolith growth and produces a dark ring in the otolith microstructure.
These dark rings may be then viewed by fisheries managers with transmitted light.
Because Alaskan water temperatures are very cold, its hatcheries would have to
raise the temperature of there water first before they could rapidly drop it. By planning
a sequence of temperature changes, a hatchery is then able to produce a pattern of
dark rings within the otolith of all fish subject to those temperature changes.
These planned hatchery temperature changes will produce a sort of discrete bar coding
within the otolith and may then be later viewed with transmitted light.

Using mass Thermal Marking technics, fisheries managers need only clip a fin
of a hatchery salmon to later identify where it came from.

Isn't Science Wonderful !

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