The age of fish can be determined by studying their otoliths. Similar to trees, otoliths have annual growth rings. In addition, based on the size of an otolith, the length and weight of the fish can be predicted.
An otolith is a structure in the inner ear of fish that is composed of calcium carbonate crystals and a gelatinous mass. Otoliths play a role in the mechanical perception of sound, acceleration and gravity.
Because these otoliths have a specific shape for every fish species, they can also be used for diet studies of their predators, such as seals. For this purpose, otoliths are isolated from faeces.
In the otolith lab there are various facilities to process otoliths for age determination: beside preparation methods as mounting in liquid plastic and breaking and burning, there are also facilities to make sections of otoliths. For the method mentioned last, the otoliths are embedded in resin and cut with a LABCUT 230 sawing machine through the centre and glued on glass slides.