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How To Preserve Fish Specimens for Long-Term Storage or Shipment
A: Museum collections are an irreplaceable resource.
B: 10% formalin solution.
C: If possible lay jar on side during fixation.
D: Example data sheet.
F:Carefully wrap specimens in damp cloth and seal in plastic.

Preserved fish specimens are central to documenting and describing global biodiversity through time. Worldwide, museum and university collections provide irreplaceable resources and have an enduring role in taxonomic, ecological, biogeographical, and evolutionary studies. If correctly preserved and handled specimens can last, more-or-less intact, for centuries. It is therefore important that the correct preservation procedures are followed to ensure the quality and longevity of preserved fish specimens.

If not already dead at the time of collection fish should be killed by application of a lethal dose of anesthetizing solution. Anaesthetized fish relax and can be preserved in a fully natural state. Common fish anesthetics include: MS222 (tricaine methane sulphonate) a white water-soluble powder that is stable when kept cool and dry. Benzocaine (ethyl aminobenzoate) a colorless crystaline or white powder that is cheaper than MS222 but a little less effective. 2-phenoxyethanol (phenyl cellosolve) a colorless oily liquid is among the cheaper fish anesthetics.

However these chemicals are all relatively expensive and often difficult to obtain in developing countries, and also may have potential harmful human side effects if not carefully used.

An excellent, cheap and widely available alternative is clove oil or eugenol. Clove oil is available at most pharmacies worldwide. It is not readily water-soluble and should be mixed with ethanol before addition to water. A useful article on the use of clove oil as cheap and effective eco-friendly alternative is available here.

Specimens should be rinsed in water to clean off any mud or sand. If tissue vouchers are to be taken then this is the time to do it BEFORE the specimen is fixed in formalin. Methods for taking tissue vouchers are described here. Prior to long-term preservation specimens will need to be fixed as soon as possible to prevent further breakdown of tissues.

FORMALIN is the best available fixative and is widely available from pharmacies worldwide. Full strength liquid formalin purchased in pharmacies is 37% formaldehyde dissolved in water. For adequate fixation in warm climates it is important to make a strong formalin solution. We recommend that for collections made in Congo a mix of ONE PART full strength formalin to FIVE parts clean water is used. While a "10%" formalin solution is usually recommended for fish fixation (this is made by combining 1 part full strength formalin with 9 parts clean water - the resultant dilution is actually only 3.7% to 4% formaldehyde) we find that this is not strong enough to properly fix specimens in Congo. Adequate initial fixation is critical for long-term preservation. Note that formalin is slightly acidic, and long term storage of fish in unbuffered formalin can result in bone deossification so it is best to add some marble chips, crushed oyster shell, or a few ml of borax to neutralize the formalin stock solution.

NOTE: formalin is highly toxic and its fumes should not be inhaled. Rubber gloves should be worn while using formalin or handling formalin fixed specimens. If you get formalin on your skin or in your eyes wash it off with large amounts of water. Always use formalin outdoors or in a well-ventilated area.

FIXATION: Fish specimens should be fixed in a natural posture, so try to straighten bodies, close open mouths and arrange fins prior to fixation. Place the specimens head first into a wide-mouthed jar filled with enough 10% formalin solution to cover the fish.

Place a watertight lid on the jar and lay it on its side. Where possible fish should float freely to avoid curling or bending. Specimens should be left in this solution for several days. Fishes of 150 cm or smaller will need to be fixed for 2-5 days, larger specimens should be fixed for 7-10 days.

Before fixing large specimens it is advisable to inject formalin into the body cavity (through the vent) or to make a lateral incision on the right side of the body cavity to allow the fixative into the body cavity. This is particularly important with large herbivorous fishes, as their guts will rapidly deteriorate.

Different species captured at the same site can be fixed and stored together but do not to pack the jar too fully.

Place a waterproof paper label in the jar noting the field site number of the collection, the date of the collection, the locality of the collection, and the name of the collector/s. The labels should be written with a soft pencil not in ink. The field site number provides a link to all of the data that should be recorded by the collector in a field notebook. An example of a field notebook entry is shown above in the lefthand column.

LONG-TERM PRESERVATION: Once specimens are fully fixed (they should be well hardened and rigid) they can be transferred for long-term storage in alcohol, or wrapped for shipment to a museum. Formalin should be decanted off (this formalin can be reused but it is advisable to add enough full strength formalin to bring the dilution strength back to 10% for future use). Specimens should be rinsed in water a few times to remove excess formalin, and then transferred to and stored in 70% ethanol, or 50% isopropyl alcohol. If alcohol is not available for long-term storage, specimens can be stored in formalin. If formalin storage is the only option then care should be taken to ensure that the formalin is well buffered and maintained at neutral pH.

SHIPMENT: For shipment of formalin fixed specimens the following procedure is recommended: Specimens should be soaked in water overnight to remove all excess formalin. Strips of cheese cloth, muslin, or loose weave cotton should be dipped in water and excess water squeezed out so that the strips are moist but not dripping wet. Specimens should then be wrapped in the damp material so that each specimen is covered and protected. The material covered specimens should then be place in a plastic bag, along with a clean label noting the field site number. The plastic bag should be tightly sealed and placed within another plastic bag to ensure that the specimens remain moist. Once packed the specimens may be boxed and shipped. Fully fixed specimens that remain damp may safely be stored for at least a month, although the sooner they can be unpacked, sorted and preserved in alcohol the better. Different species captured at the same site can be fixed and stored together but do not to pack the jar too fully.

NOTE: A useful manual outling more details on fish collection methods and standards is available here.

© 2007 American Museum of Natural History Back to Ichthyology Department