Using otoliths
Cefas has nearly 30 years experience of sectioning otoliths.The mounting and sectioning
facility, started in 1977, is now one of the most advanced of its
type in Europe. Upwards of 50,000 otoliths are currently sectioned
annually using three cutting machines fitted with diamond
blades.
Otolith Processing
Once sectioned, the otoliths can be aged under transmitted or
reflected light and are ideal for long-term storage and re -
analysis if required. Sectioning greatly improves the visibility of
the ring structure and the speed and accuracy with which otoliths
can be read.
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Mounting cabinet with video
display
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Moulds being prepared with cod,
haddock
and plaice otoliths
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Haddock otoliths being
sectioned
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Slide of cod otoliths viewed by
transmitted light
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Pelagic Species
Small otoliths from pelagic species such as herring, mackerel
and sprat are not sectioned. They are mounted whole onto black
slides and covered with clear resin and a glass cover slip. The
ring structure can then be seen clearly on the whole otolith using
reflected light.
Otolith Staining
In addition to sectioning, Cefas has developed a staining
procedure that can significantly improve the readability of species
such as sole, brill, turbot, dab, flounder and tropical
lethrinids.
A thin band of protein laid down at the end of each hyaline zone
is stained using neutral red dye with acetic acid added.
Key features of the Cefas age determination process
- Precision mounting and cutting through the centre of the
nucleus.
- Ability to section roundfish and flatfish otoliths.
- Experience with a broad range of species and otolith types,
including cold-water, temperate and tropical species.
- Capacity to handle large numbers of otoliths quickly.
- Sections can be cut and mounted to customers'
requirements.
- Quality control and consistent accuracy are maintained
throughout the process.
Preparation and age determination services offered by
Cefas
- Otolith length and weight measurement.
- Sectioning, staining and permanent mounting of otoliths.
- Reading otoliths for age (large or small numbers), with checks
on reading accuracy.
- Validation of age of fish using otolith growth increments and
other techniques.
- Research into application to new and difficult species, and use
of other hard parts (e.g. scales, vertebrae).
- Investigation of temperature history using otolith isotope
analysis.
Technical specification
Mounting equipment - precision built mounting
cabinets with CCTV monitors for exact alignment of otoliths. All
moulds are precision made.
Cutting equipment - all with digital control to
0.01mm.
Two "V4" Superior cutting lathes fitted with
electroplated diamond blades.
Accutom-50 precision cutting machine fitted
with metal-bonded diamond blade.