Fixation and preservation of plankton

A fixative, such as formaldehyde, chemically treats the tissues: stopping biochemical activity and increases the mechanical strength. A preservative, such as alcohol or salt, is a natural compound that reduces or stops decomposition without chemically fixing the tissue. Samples preserved in alcohol may shrink or become distorted more than in formaldehyde, but are safer and more pleasant to study, and are suitable for DNA analysis. Therefore the type and amount of fixative/preservative used should be determined by the sampling objective and the size of the samples being collected (Table 4.2). If preservatives are not available, the samples should be kept cold - either stored in a refrigerator or stored in a portable icebox. Under these conditions, however, the samples are only viable for a period of 1-2 days.

Table 4.2. List of possible plankton fixatives.

Phytoplankton fixative

30% methylated spirits 5% glutaraldehyde Lugol's solution* Tincture of iodine* Acid Lugol's 2% formaldehyde

Microzooplankton fixative

2% formaldehyde

Macrozooplankton fixative

5% buffered formaldehyde (3 7% formaldehyde with sodium tetraborate or hexamine).Rinse and transfer to 70% alcohol for long term preservation.

*NB: When adding tincture of iodine or Lugol's to the sample, do so 'drop by drop' until the sample turns a dark tea colour.

*NB: When adding tincture of iodine or Lugol's to the sample, do so 'drop by drop' until the sample turns a dark tea colour.

Formaldehyde is usually made from the oxidation of methanol, using silver or copper as a catalyst. The concentration provided by the manufacturer is typically a 40% solution, with a trace of methanol to reduce polymerisation to paraformaldehyde (a white precipitate - which may be cleared by warming or with a few pellets of sodium hydroxide). This concentrated solution is pungent and carcinogenic (Box 4.9). Sometimes it is hard to tell (during arduous or sleepless field conditions) if formaldehyde has been added to the plankton sample. A few drops of a stain such as eosin in your 40% stock solution is a useful indicator.

You only need a very dilute solution to preserve plankton, and such dilutions are sometimes termed 'formal', 'formol' or 'formalin', but these are imprecise and are discouraged. A 4% solution of formaldehyde (such as for preserving fish or macrozooplankton) is made up from 10 mL of the 40% commercial or concentrated grade and 90 mL of sea water or fresh water. This solution should be referred to as '4% formaldehyde', not as '10% formalin' (as this author and others have sometimes used). Similarly, for preserving zooplankton, a 1 or 2% formaldehyde solution is used, which is made from 25 or 50 mL of 40% concentrated formaldehyde and made up to 1 litre (Steedman 1976). This may also be buffered with a few marble chips. In a tightly sealed jar, this solution is stable for decades if stored in a cool and dark location. Do not squeeze too much plankton into a sample jar - the volume of plankton to solution should be about 1:9 (Steedman 1976).

Before sorting such a sample, it is best to gently rinse off the formaldehyde solution thoroughly in fresh water, and transfer to 70% alcohol as a preservative. Alcohol is a good long-term preservative, but it does not fix animal protein histologically. Formaldehyde solution may be buffered with sodium carbonate (NaCO3, purchased cheaply in bulk as 'soda ash') as a 5% formaldehyde solution becomes slightly acidic, which dissolves calcium carbonate, including larval fish otoliths (which are used to determine age

BOX 4.9 OCCUPATIONAL HEALTH AND SAFETY

Note that fixatives and preservatives are poisonous and some are probably carcinogenic. Adequate care should be taken at all times. Examination of live, non-preserved samples is best. Otherwise all samples should be preserved immediately, or should be placed in dark cool containers (eskies or fridges) to ensure that no further primary production or grazing can take place. Consult with the personnel at any identification laboratories regarding the method they require and remember that some researchers also like to get a separate live sample that can aid them with the identification of small flagellates and ciliates.

and daily growth). After a few weeks, buffered larvae suffer bleaching of their black spots (melanophores). It is best to transfer fish larvae to 95% alcohol within weeks of capture (70% alcohol is also slightly acidic).

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Responses

  • Harrison
    How preservative fix the plankton?
    3 years ago
  • irvin
    What is plankton fixation?
    3 years ago
  • jonna
    Why lugol's solution is used to preserve phytoplankton samples?
    3 years ago
  • lotta
    How to preserve planktons?
    2 years ago
  • gianfranco castiglione
    Why lugol for preservation of phytoplanktons?
    2 years ago
  • heikki
    How can we preserve plankton?
    2 years ago
  • nelma
    How to fix zooplankton?
    2 years ago
  • Cailyn McIntosh
    How to fix the plankton sample?
    2 years ago
  • MIMOSA
    How to preserve zooplankton samples?
    2 years ago
  • DAVID
    How can we fix the decline of plankton?
    2 years ago
  • lete
    Can we use lugol to preserve zooplankton?
    2 years ago
  • hayley
    Why do we preserve plankton with formalin?
    2 years ago
  • Annunziata Fiorentini
    Do plankton have to be stored in a cold container?
    1 year ago
  • asmara
    Why to preserve planktons in 4 formaldehyde?
    1 year ago
  • katherine jones
    Can you use alcohol as a fixative for plankton?
    1 year ago
  • Amanda
    How to preserve plankton samples?
    12 months ago
  • semrawit
    How topreserve planktons?
    7 months ago
  • Cora
    What is the different fixation and preservation in planktons sampling?
    4 months ago
  • Adelgrim
    What is fixing in plankton analysis?
    3 months ago
  • thomas
    How to Zooplankton fixation?
    1 month ago

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