[Histonet] Re: AFA fixative

[RSRICHMOND <@t> aol.com]

Cristina De Amaral P. Nunes at the INIAP-IPIMAR Fisheries and Sea Research 
Institute Marine In Lisbon, Portugal asks:

>>For several years, in the Institute where I am working, the main fixative 
used for the preservation of gonads of fish was AFA, with apparently good 
results. Then, at a given moment (before I arrived to the Institute), it was 
decided to change from AFA to a formalin solution because of the higher toxicity of 
the former. The histological results were slightly less good but for practical 
reasons (most fish tissue fixations occur at sea, on board the research 
vessels), it was considered to be the best solution.<<
and Geoff McAuliffe notes that >>AFA is alcohol + formaldehyde + acetic acid.<
<

Assuming that AFA is indeed similar to Davidson's fixative, it would probably 
be a better fixative for gonadal tissue. I think there are two reasons not to 
use it for tissue fixation at sea, partly its toxicity (including possible 
fire hazard, depending on its composition), but also because the fixative will 
damage tissue (with loss of nuclear basophilia) if exposure to the fixative is 
continued much past 24 hours. I think that phosphate buffered formalin 
(neutral buffered formalin) would probably be the fixative of choice.

AFA would be more toxic than neutral buffered formalin because of its higher 
formaldehyde content, its acidity, and the presence of alcohol, to say nothing 
of its unpleasant and penetrating ("airplane dope") odor. Pathologists use it 
to locate lymph nodes in fatty tissue, and it's unpleasant to handle even 
with good ventilation and high quality gloves - it degrades gloves (including 
some nitrile rubber gloves) rapidly

Bob Richmond
Samurai Pathologist
Knoxville, Tennessee USA