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Alaska Age and Growth Procedures for Otolith Examination

Learn more about the break-and-burn procedure for studying age and growth of otoliths.

Age and Growth Program Thin Sectioning ProceduresAge and Growth Program Thin Sectioning ProceduresAge and Growth Program Thin Sectioning ProceduresAge and Growth Program Thin Sectioning Procedures

Otoliths at the Alaska Fisheries Science Center are typically prepared and processed using the break and burn method. This method begins by placing the whole otolith in a petri dish that is lined with a black, felt background and enough water to completely submerge it. The surface of the otolith is viewed under a dissecting microscope at about 10x magnification.

The whole otolith is placed in clay, which has been mounted on a chuck of the low speed saw, then cut in half. Using forceps, one of the otolith halves is held over the flame of an alcohol burner until it becomes caramel colored. This process allows the protein called otolin to react with the heat, and display the annuli. 

The burnt otolith half is placed in a dish of clay and examined under a microscope on 40x magnification. Annuli (the rings or bands) are counted and an age estimate is recorded for the sample currently being examined. 

All ages are entered into a database and a randomly select sample of 20 percent is selected and independently examined, or "tested," by a second age reader. Using a statistical program, ages assigned by the first age reader are compared with the ages assigned by the second age reader. We record the percent agreement between the two readers and compare these figures with other tests on record for the same species. All differences or discrepancies are resolved between the readers, and then ages are used in the stock assessments.