Otolith Age Reading by Means of Surface Structure Examination

Abstract

Surface microscopy (as used in metallography) shows the finer structure in the otolith and often clearly reveals annual rings, even in older fish. Measurements are easily made on specimens or on photographs. Examination of the flat, polished, surface of the otolith reveals a pattern of concentric lamellae of different thickness. Groups of thin lamellae often form rings which correspond to the dark year rings in a burned otolith. With surface illumination such rings can be found in otoliths which could not otherwise be read. The technique of embedding, cutting and illuminating otoliths for surface microscopy is described.