Caractérisation du comportement chimique du complexe otosac-otolithe et réaction à des perturbations induites.

Teleost fish have the capacity to record in their otoliths, calcareous concretions located in the inner ear, the principal events (environmental and physiological) which punctuate their life. Otolith is made of CaC03 deposits on a protein matrix according to a circadian rhythm. Due to the quasi irreversibility of this process, otoliths can be compared to biological archives largely used to apprehend the fish ecology. The otolith bathes in the endolymph, a medium in which all the precursors of otolith formation forward. The endolymph chemical analysis revealed a heterogeneity of its principal components (proteins, total C02 and total Ca) which origin lies in the non uniform spatial distribution of the ionocytes in the saccular epithelium. Thus, in relation to the asymmetrical morphology, these endolymph chemical gradients made it possible to propose a model of otolith calcification. In addition, the analysis of the circadian variations of the endolymph concentrations of proteins and total C02 underlined the preponderance of the endolymph composition in the otolith biomineralisation process. The studies of the repercussions of environmental disturbances (chlorinated water, change of salinity and temperature) on the chemical composition of the endolymphe and the otolith consolidated the assumption of a close bond between these two compartments. These environmental changes caused chemical and structural modifications of the otolith reflecting variations of the concentration of the endolymph components.