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Frequently Asked Questions

What is specimen fixation?

Alcohol fixed (AMS I. 41084-076) and formaldehyde fixed (AMS I. 41084-075) Crimson-banded Wrasse collected at Watsons Bay, Sydney Harbour, December 2001. View larger image

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.

The fish in the image are juvenile Crimson-banded Wrasse Notolabrus gymnogenis (view fact sheet for this species). The difference in colour after fixation is immediately apparent. Also note the white colour of the eye lens in the alcohol fixed fish.

The two fish were collected at Watsons Bay, Sydney Harbour in December 2001. The images were taken about three weeks after fixation. The formaldehyde fixed fish was fixed for eight days before being transferred to alcohol.

View low resolution movie clips on why we collect fishes (67k), fixation in formaledhyde (177k) and preservation in alcohol (217k). Go to the movies page for high and low resolution versions.