[Nhcoll-l] [MOGELIJK SPAM ! *****] Re: Preserve fish specimens

[a.j.van_dam at lumc.nl]

I rest my case...


--Dries

Andries J. van Dam<http://www.linkedin.com/in/andriesvandam> | curator-conservator

Anatomical Museum<https://www.lumc.nl/onderwijs/over-ons/anatomisch-museum/?setlanguage=English&setcountry=en> | Leiden University Medical Center | Building 3 (V3-32)
P.O.Box 9600 | 2300 RC Leiden | The Netherlands
Visiting address: Hippocratespad 21 | Tel: +31 (0)71 52 68356 | E-mail: A.J.van_Dam at lumc.nl<https://mail.lumc.nl/owa/redir.aspx?C=O7wgy__4qEq-bCzDQhMP7IpMG33lsdEIUTcpXTatWwljNFWdpbtnBKj-HeYnbumJrkd3hILExAk.&URL=mailto%3aA.J.van_Dam%40lumc.nl>

Scientific associate | Natural History Museum London | http://www.nhm.ac.uk<https://mail.lumc.nl/owa/redir.aspx?C=O7wgy__4qEq-bCzDQhMP7IpMG33lsdEIUTcpXTatWwljNFWdpbtnBKj-HeYnbumJrkd3hILExAk.&URL=http%3a%2f%2fwww.nhm.ac.uk%2f>
________________________________
Van: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> namens John E Simmons <simmons.johne at gmail.com>
Verzonden: zondag 18 september 2022 20:09:59
Aan: Maxine C
CC: NHCOLL-new
Onderwerp: [MOGELIJK SPAM ! *****] Re: [Nhcoll-l] Preserve fish specimens

I agree with Dirk--it is not possible to preserve the colors found in living fish (or any other organism) by preseCorvation in fluid preservatives. There are several factors to consider, including:
1-Color comes from a combination of pigments (many of which are photosensitive or subject to alteration by the fixatives or preservatives) and the reflection and refraction of light, so that any shrinkage or swelling is likely to alter color even if the pigments are not affected.
2-In most organisms, color is not stable. Some colors are temporal (depending on the time of year), affected by the environment, the age of the organism, or the time of life of the organism (for example, colors that show only during mating season).
3-The perception of color of an organism by a human being may be very different from how the color is seen by other species.

Over the last 200 years, there have been dozens of recipes published for the preservation of color or restoration of color in preserved tissues. The one element linking all of these publications is that very few of them used an accurate color reference standard. Instead, a researcher would look at the specimen weeks or months after preservation and pronounce its colors to be lifelike without reference to what the colors were at the moment of preservation. Without a color reference, it is impossible to look at a specimen and claim that its colors have not changed. I reviewed several of these recipes in my book, Fluid Preservation: A Comprehensive Reference (https://www.amazon.com/Fluid-Preservation-Comprehensive-John-Simmons/dp/1442229659).

It is not possible to avoid swelling and shrinkage of specimens during preservation, either, but it can be minimized. The dimensional changes that an organism goes through during fixation and preservation are highly variable, even within a species (I reviewed the literature on dimensional changes during fixation and preservation in the above mentioned book as well). Dimensional changes result not only from the fixative and preservative chemicals used, but also how the specimens are handled, euthanized, the time interval between death and fixation or preservation, and the light exposure that a specimen is subjected to during the process of preservation.

There are a few things you can do during preservation that will keep the change of color as well as dimensional changes at a minimum (but you cannot save the actual colors of the organism at the time of its death, and specimens will undergo body mass changes during preservation):
1. Keep the specimen in the dark as much as possible (particularly away from sunlight, which is rich in ultraviolet radiation), both during fixation and subsequent preservation.
2. Minimize the length of time the specimen is kept in a formaldehyde-based fixative (depending on the specimen size and surface-to-volume ratio, this may mean a few hours or a few days).
3. Keep the specimen at cool (but not cold) temperatures (heat accelerates the chemical processes that cause color changes).
4. Stage specimens through concentration steps of about 20% each as you move the specimen from the formaldehyde-based fixative to an alcohol-based preservative.
5. Prepare fixative and preservative fluids using the cleanest water possible (ideally, deionized water). Do not use denatured alcohol. There is no evidence from controlled studies to indicate that glycerine will preserve colors any better than ethyl alcohol, and there are too many uncontrolled variables to make that assumption based on examination of specimens post-preservation.

The only way to preserve an accurate record of the colors of an organism at the moment of its death is to take photographs. However, there are many variables that can affect color rendition in photographs as well, such as light intensity, light color, and the equipment you use. To be able to correct for these factors later, always include a color scale in the photograph. It is not possible to make accurate color corrections in images (whether analog or digital) without having a scale in the original photograph. There are many color scales you can get for use in the field, such as this one: https://www.bhphotovideo.com/c/product/714596-REG/Tiffen_EK1527654T_Q_13_Color_Separation_Guide.html/?ap=y&ap=y&smp=y&smp=y&lsft=BI%3A6879&gclid=CjwKCAjwg5uZBhATEiwAhhRLHsmNShKFUMn2utxapxXxbKQCGo_o1z68Xqmr2tMnLTxSDW6AJrX9LxoCcBoQAvD_BwE

--John

John E. Simmons
Writer and Museum Consultant
Museologica
and
Associate Curator of Collections
Earth and Mineral Science Museum & Art Gallery
Penn State University
and
Investigador Asociado, Departamento de Ornitologia
Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima


On Fri, Sep 16, 2022 at 7:44 AM Maxine C <cutraccimaxine at gmail.com<mailto:cutraccimaxine at gmail.com>> wrote:
Hi all,

I'm working on a research project at the University of Hong Kong on fish biodiversity. We would like to preserve very small cryptobenthic fish species ( 5 - 10 mm in length).
In the past, I've used formalin and ethanol 70% but I'd like to preserve the coloration.

Any advice? Would resin work?

Regards,

Maxine
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