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Changes in gill ionocyte function and structure following transfer from fresh to hypersaline waters in the tilapia Sarotherodon melanotheron

Ouattara N., Bodinier C., Negre-Sadargues G., Messad S., D'Cotta H., Charmantier G., Panfili J., Baroiller J.F.. 2008. Comparative Biochemistry and Physiology. Part A, Molecular and Integrative Physiology, 150 (3) : S103. Annual Main Meeting of the Society of Experimental Biology, 2008-07-06/2008-07-10, Marseille (France).

DOI: 10.1016/j.cbpa.2008.04.214

The effects of salinity were investigated in the black-chinned tilapia Sarotherodon melanotheron heudelotii originating from a hypersaline estuary (Saloum, Senegal). Under controlled conditions, juvenile fish originally kept in freshwater (FW) were divided into two groups exposed to FW or directly to 35 psu seawater (SW). Part of these SW fish were then acclimatised to hypersalinewaters (HW) by a step-wise increase of 7 psu/day up to 70 (HW70) and 90 (HW90). Three major ion transporters, Na+/K+-ATPase, the cotransporter Na+/ K+/2Cl- (NKCC) and the Cl- channel (CFTR) were localized by immunofluorescence in the gill ionocytes and changes regarding ionocytes localization, number and sizes were investigated. In FW, Na+/K+-ATPase immunostained ionocytes were only observed at the base of the filaments, whereas in SW and HW they were localized on both the filaments and the lamellae suggesting that lamellar ionocytes could also be functional in SW. A significant increase in ionocyte number and size (area) occurred following transfer from FW to HW. Although the cell number remained constant between HW70 and HW90, their size increased from FW to HW90, indicating that the size and shape of cells could be a sensitive indicator of osmoregulation in HWin this tilapia. In FW, NKCC stainingwas concentrated at the apical region and CFTR was not observed. In SW, Na+/K+-ATPase and the cotransporter NKCC were colocalized on the basolateral membrane, while CFTR was located at the apical region.

Mots-clés : sarotherodon melanotheron; eau douce; eau saline; osmorégulation; salinité; branchie; cytologie; développement biologique; hydrolase; sénégal

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