Gill Epithelium Ultrastructure of Oreochromis niloticus Exposed to Gradual Raised Salinity

Fish gill is a multifunctional organ with role in acid-base balance, elimination of nitrogen waste and mainly gas exchange and ion regulation. There is a high energetic coast for ionregulation in freshwater fish maintained in salt water but a raise in growing taxes was observed for some species. The freshwater Nile tilapia, Oreochromis niloticus, is widely used in aquaculture farmers and the aim of this study was to investigate the changes on the gill filaments ultrastructure in fish kept under different salinities. Alevins were obtained and transported to laboratory of studies in animal stress Federal University of Paraná. Established groups in 0‰, 16‰ and 32‰ salt water with 12 animals in each one. After 30 days of exposition, the animals were anesthetized and the second gill arches were dissected and processed for scanning and transmission electron microscopy. The mitochondrial rich cells fractional area and density in the gill epithelia were determinated. The under scanning electron microscopy (SEM) in 0‰ salinity group reveal changes in the apical ridge of mitochondrial rich cells (MRCs). In all other groups, the observations revealed numerous crypts disposed mainly in the filament epithelia. In transmission electron microscopy (TEM) two distinct types of MRCs were observed. The data of MRCFA and density revealed in 0‰ and 16‰ values significantly elevated in comparison to 32‰. Despite these lower values, the density in the gill epithelia was higher. The main differences found between the groups revealed that fish exposed to 16‰ salinity have less MRCs aperture to the environment and are less related to ion regulation process.

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