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 fishes' 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 several facilities for processing otoliths for age determination: besides preparation methods such as embedding with liquid plastic in a display plate and breaking and burning otoliths, there are also facilities for making sections of otoliths. For the latter method, the otoliths are embedded in synthetic resin, sawed through the core using a LABCUT 230 sawing machine and ultimately glued to glass slides.