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Stones in the head of a fish – is that possible? In Namibia, some anglers are aware of stones, or otoliths, in the head of the Madagascar meagre, but it is not generally known that ear-stones, most of them tiny, are found in the skull of all fish. Ear-stones, according to scientists, probably help fish to keep their balance. Otoliths are white and very hard, as they consist mainly of calcium carbonate (aragonite). They are embedded in a jelly-like substance behind the eye and located in a bone cavity. The otoliths in the left and the right side of the head are shaped in a mirror image of one another.

Otoliths are used to find out what Cape fur seals eat on our coast. Scientists dry the faeces of seals, then grind and sift it to finally pick out the white otoliths. Each fish species can be identified thanks to the unique shape of the ear-stones, and based on its annual rings the age of the fish eaten by a seal is determined. 

For further information of otoliths, please have a look at Namibia Outdoor.