engleski

Occurrence of calcite in saggital otoliths of whiting Merlangius merlangus (Linneaus, 1758) from the northern Adriatic Sea.

Otoliths are a part of the inner ear where they form an organ used for hearing, orientation and balance. Saggital otoliths of teleost fish are usually composed of calcium carbonate crystals in the form of aragonite, but abnormal otoliths containing other polymorphs, vaterite and calcite, have been reported, and this type of modification in otolith crystallization was described by Palmork and Taylor (1963) as Type II. In this work normal otolith shape is distorted and abnormal areas contain calcite only. This is the first record and investigation of abnormal calcite otoliths in whiting. The mechanism of formation of abnormal otoliths remains unknown. Factors that may trigger this change include stress, food, virus infection, pollution, temperature or some kind of mechanical damage to macular cells (Strong et al., 1986) that can trigger a change in the organic precursor for the deposition of the crystal lattice. Elevated Mg concentrations found in this study are consistent with calcitic areas that is likey related to a different organic matrix and growth regime which requires further investigated. Tomas and Geffen (2003) suggested that natural selection favoured fish with normal otoliths, which results in a lower frequency of abnormal otoliths in adult than in juvenile fish. Even though our sample was small, it showed that the condition index of whiting was negatively correlated with extent of calcitic area on the otolith, which may lead to a higher mortality. Although Dion et al. (2007) found that the occurence of vaterite sagittae was associated with significant hearing loss in Chinook salmon, it seems that fish can compensate for the differences in the information received by one of the two ears, or simply rely more on visual cues and grow into adulthood, as do the whiting analysed in the study which ranged from 18 to 27 cm long.

otolith; calcite; deformation; Merlangius merlangus

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