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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.

Mounting cabinet with video display
Mounting cabinet with video display

Moulds being prepared with cod, haddock and plaice otoliths
Moulds being prepared with cod, haddock
and plaice otoliths

Haddock otoliths being sectioned
Haddock otoliths being sectioned

Slide of cod otolith viewed by transmitted light
Slide of cod otoliths viewed by transmitted light

Slide of 25 herring otolith pairsPelagic 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.

Stained sole sectionsOtolith 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.

Stained sole otolith age 4 years

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.

© Crown Copyright 2014
Last Modified: 27 April 2014