[Nhcoll-l] formalin fixed internal parasites

[Jean-Marc Gagnon]

James,

Since your request did not seem to stimulate lots of responses (at least not on NHColl), I thought I could share a bit of information from my limited experience.

I initially intended to include free-living marine nematodes in my Ph.D. research but opted not to for a number of reasons. Still, working with them and particularly transferring them to glycerine to facilitate the observation of mouthparts thought me a few things.

First, any change in H2O concentration in the preservation fluid can cause significant “osmotic shock”, easily observed by the collapsing/twisting of specimens. It seems that their cuticle plays a major role in selecting the size of molecules penetrating and /or determining the speed at which they penetrate. If I changed the solution too quickly from a 3-5 % formaldehyde to ethanol, even in a stepwise increase in concentration to ultimately reach 70-80%, the specimens would “shrivel”. That’s a significant risk of physical damage.

The other risk from transferring certain groups of invertebrates from a formaldehyde solution to ethanol is the fact that some will become more opaque and their internal structures become less visible, if at all. I am not sure that’s the case for nematodes but it certainly is for certain groups like planktonic copepods and chaetognaths. The decreased access to these morphological characters may reduce the scientific value of these specimens.

I am sure someone out there will know more about this. I strongly suggest that before you attempt any major change over of fixative/preservative, you should test the procedure and its effects.

My two cents…

Jean-Marc

Jean-Marc Gagnon, Ph.D.
Curator / Conservateur des collections
Invertebrate Collections / Collections des invertébrés

Canadian Museum of Nature / Musée canadien de la nature
P.O. Box 3443, Stn "D" / C.P. 3443, Succ. D
Ottawa, ON Canada K1P 6P4
T: 613-364-4066 / F: 613-364-4027
E/C: jmgagnon at mus-nature.ca<mailto:jmgagnon at mus-nature.ca>
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From: nhcoll-l-bounces at mailman.yale.edu [mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of James Cokendolpher
Sent: August-05-15 9:11 PM
To: Nhcoll-l at mailman.yale.edu
Subject: [Nhcoll-l] formalin fixed internal parasites

I have been following the current "rehydrating a formalin specimen" e-mails.  We have several jars of dried nematods that I will be trying to rehydrate.  My thoughts now are more to parasites that were fixed and currently remain in pH buffered formalin.

Should specimens like nematods, cestodes and the like remain in this solution forever if they originally were fixed in this solution?

We want to catalog the formalin collection but wondered if it could be transferred to ethanol without damaging the microscopical features first.  Is there a internet discussion list established for curators/workers with soft-bodied invertebrates?  My desire to work with vials of ethanol versus formalin is primarily for safety and future ease of housing the collection.

Thanks in advance for any guidance,
James
-------------------------------------------
 James Cokendolpher
 Invertebrate Zoology
 Museum of Texas Tech University

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