FAQ - What is specimen fixation?

There is sometimes confusion over the term 'fixation'.  What is 'specimen fixation?'

A White Shark in the tank area

A White Shark in the tank area
Photographer: Jason Armstrong © Australian Museum

For the last 80 years, fishes in the Australian Museum fish collection have been fixed in formaldehyde and then stored in alcohol.

Fixation using formaldehyde is a chemical process during which the proteins in the specimen are cross-linked. Fixation prevents the breakdown of tissues resulting from the release of enzymes after tissue death (autolysis).

Formaldehyde fixation results in hardening of the tissues. This is desirable for the long-term durability of the specimen.

Formaldehyde fixation involves immersing the specimen in 10% formaldehyde for several days up to weeks depending upon the size of the fish. Specimens are then stepped up through a series of alcohol baths of different concentrations. This procedure produces excellent specimens that can be used for a wide range of research and other uses (more information).

Prior to the use of formaldehyde, specimens were usually fixed in alcohol. Over the last 10 years we have resumed fixing specimens in alcohol, in addition to fixing fishes in formaldehyde. Both methods of fixation have their advantages.

Alcohol fixed specimens (and frozen tissues) are increasingly being loaned to researchers who are conducting genetic work. These workers need tissues that have been fixed in alcohol (or frozen), not formaldehyde, because formaldehyde changes the DNA in the sample.

Mark McGrouther , Collection Manager, Ichthyology
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