Tentative application of computed tomography to study of otoliths and their responses to environment variations

As the carrier of biomineral aragonite, fish otoliths memorize various messages of environment throughout the fish’s life. In the past three decades, quite a few achievements have been made in the studies of fish otoliths, but no advances in research using medical instruments have been reported. The authors tentatively applied X-ray computed tomography (CT) to the studies of the internal structure of wild carp otoliths, with the CT value determined by variations in the sample density and element composition. The wild carps were collected, respectively, from the Baiyangdian Shallow Lake in Hebei Province and Miyun Reservoir in the Beijing metropolis, whose water environments are quite different. The former has suffered serious pollution and eutrophication, whereas the latter has nearly experienced no pollution. The primary result indicates that differences exists in CT values of otoliths for the carps from the above-mentioned waters. With in-depth studies, it is possible that X-ray computed tomography could serve as a useful tool in the study of fish otoliths, and the CT values can be taken as typomorphic parameters to distinguish the waters with different degrees of pollution.