[Nhcoll-l] Preserve fish specimens

[John E Simmons]

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> 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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