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Preliminary results on the chemical composition of the Lepidorhombus boscii (Risso, 1810) otolith from the Adriatic sea

Otoliths are a part of the fish inner ear involved in sound reception, balance perception and orientation. Saggital otoliths of teleost fish mainly consist of calcium carbonate in the form of aragonite. However, there are abnormal otoliths that contain other polymorphs, such as calcite, vaterite or their combinations. This preliminary study represents the first record and investigation of Lepidorhombus boscii otoliths including those irregularly shaped and characterized by surface deformations. These can arise due to stressful conditions, high population density, temperature fluctuations, disease or pollution, which can cause structural or physiological changes that affect the formation of otoliths. In addition to morphological features, polymorphs of calcium carbonate have an influence on the elemental composition of otoliths. The morphology and chemical composition of L. boscii saggital otolith were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and by two step laser desorption ionization mass spectrometry (L2MS). L2MS was used to analyse the surface chemical composition of the otoliths, confirming the presence of inorganic and organic compounds in the otolith matrix. Tuning the desorption fluencies to maximize the metal containing components (K, Ca, Cu, Ag, Sr), shows an abundance of pure metallic, oxidized and hydroxidized species. XRD was used to analyse the crystal structure, while SEM was used to photograph the surfaces of normal and abnormal otoliths (aragonite and calcite) between males and females. This research provided a preliminary insight into the concentrations of chemical elements deposited on the otoliths of individuals of this species in the central Adriatic Sea. Although the number of analyzed samples is small, the results are promising. They represent a starting point for the future research, that should be based on a larger number of samples from more locations These results could be used to get a better insight into movement patterns and possibly for determination of the origin of this species.

Lepidorhombus boscii ; Adriatic sea ; otolith ; scanning electron microscopy ; X-ray diffraction ; mass spectrometry

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