Page 113 - Freshwater-Biology-and-Ecology-Handbook

12.3 Preserving

samples and specimens

Samples can be sorted and identified live as soon
as possible after collection, ideally within 48 hours,
including any re-analysis of live samples.

Samples must be stored between 1°C and 3°C. Any live
samples not processed within this time or not kept at this
temperature must be discarded and new samples taken.
Be aware of the risk of predators eating prey, particularly
if the sample is from a cold (upland) stream or if it is not
kept very cold or is kept for longer periods. Many taxa
such as flatworms and leeches are much easier to
identify when alive.

Fixatives or preservatives may be used if samples need
to be stored or analysis is delayed.

12.3.1 Fixative 12.3.2 Preservative

The best fixative is 5% aqueous formalin solution. Preservatives are used if samples need to be stored.
This makes specimens more robust by strengthening They stop specimens from decomposing by preventing
proteins so that limbs and other parts are less likely the growth of microbes. An aqueous solution of 70%
to detach from bodies. Fixation is only needed if industrial methylated spirit (IMS) is often used as a
specimens are to be kept for more than a couple of preservative. Replace the alcohol a number of times to
months before they are analysed. ensure that there is an adequate final concentration in
the sample. 5% glycerol may also be added when storing
individual specimens, to reduce the risk of damage
should the alcohol dry out.
NOTE The organisms should be stored in glass vials filled with

Formalin is hazardous ! ethanol, and plugged with cotton swabs. Once any air
bubbles inside the vials are removed, place the vials
and must only be used inside a larger glass container and cover with ethanol.
in a fume cupboard. The external container should be sealed tightly.

Specimens for genetic (DNA) analysis, which is not used
Many laboratories are not set up to for standard environmental monitoring assessment,
use formalin and it is no longer used should be fixed in 96% ethanol.
by most European environmental
protection authorities. Preserved samples must be stored at cool temperatures,
away from any heat source and preferably in the
dark to minimise the loss of colour. Whole samples in
preservative should be stored away from the laboratory.

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