Re: Optimising gonad preservation whilst retaining otolith microstructure

From:Geoff McAuliffe

Two grams of Calcium Acetate in 100 ml of 10% formalin is an excellent, and
often overlooked, fixative. I first read about this in Lillie's text but I don't
know if he originated it.


Dave Allsop wrote:

> Dear Histonet
> I am collecting populations of very small fish from remote locations, and
> need to extract two important pieces of information from them for my study.
> First I need to access the cellular morphology of the gonad for sex and
> maturity estimates, and second I need to access the age and growth rate
> information held in the calcified structures called otoliths (fish ear
> bones). These are Calcium carbonate concretions deposited in concentric
> layers daily or annually.
> My problem is that ideally i need a fixation method that I can leave my
> field samples in indefinitely, but that will not react with or degrade the
> otoliths. I used Bouins last time, but its acidic and degraded the otoliths.
> Normally otoliths are stored in 95% ethanol when still embedded in tissue,
> but the ethanol sometimes needs to be changed as it becomes acidic on
> reaction with the tissues. Also this concentration of ethanol would
> dehydrate the gonads and make them hard and not very good for histology.
> The best thing I can think of is NBF, but I am not sure if this will react
> with the otoliths, or how long I can leave the specimens in it. If I simply
> fix and then transfer to 50 or 70 % ethanol (as would be normal), then I
> stand to lose the otoliths (50 and 70 % ethanol is too acidic). What can I
> buffer the Formalin with that is NOT a calcium chelator? And can I leave the
> samples indefinitely in this until I get home and process them? All other
> suggestions welcome.
> Thanks
> --
> Dave Allsop
> Ashworth Laboratories
> Institute of Cell, Animal and Population Biology
> University of Edinburgh                             X>   X>
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Geoff McAuliffe, Ph.D.
Neuroscience and Cell Biology
Robert Wood Johnson Medical School
675 Hoes Lane, Piscataway, NJ 08854
voice: (732)-235-4583; fax: -4029

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