Crystal phases of calcium carbonate within otoliths of <i>Cyprinus carpio</i>. L. from Miyun Reservoir and Baiyangdian Lake, China

Abstract

Asteriscus (lagenar otolith) of Cyprinus Carpio. L. (Cyprinida, common carp) from the serious intermittent polluted Baiyangdian Lake and the little polluted Miyun Reservoir, all located in northern China, were chemically and mineralogically analyzed. All the analyzed fish showed that the composition of asterisci is dominated by calcium carbonate, with the minor elements As, Ba, Sr, and Zn; and the polymorph of CaCO₃ in the asterisci is vaterite. Three different vaterite X-ray diffraction (XRD) patterns were found in the analyzed samples. For the 60% fish from both localities, two different vaterite XRD patterns coexist in the core area and the edge area in same asteriscus sample. Significant differences of the dimensions of crystalline cells of vaterites exist between these two localities, which reveals that crystal structure of vaterite polymorphs seem sensitive to water quality and water environment, its crystalline cell dimensions might be a potential proxy for monitoring the change of water quality.

Keywords: Vaterite, biocrystallization, otoliths, microchemistry, proxy, Cyprinus Carpio. L.