The present study dealt with ultrastructural adaptation of the renal tubules of Mugil capito to different habitat salinity. Fish was obtained from the high salinity water (HSW) Lake Quaroun and low salinity water (LSW) Wadi Al-Rayan Lake, at Fayoum. The proximal convoluted tubule was subdivided into three segments (P1, P2, and P3). Cells of P1 were short and columnar with numerous microvilli, large mitochondria, RER, basal nucleus and basal infoldings. Significantly wider tubular lumen and less height in case of HSW than LSW mullet were found. Cells of P2 became higher than P1 with short brush borders, apical vacuoles and central nuclei. The basal infoldings were more elaborated than P1. Rounded, smaller and more numerous mitochondria were found. Migration of mitochondria from the basal part to the upper part in HSW mullet was observed, perhaps indicating a shift in energy demands. Three types of cells in P3 were observed, the first type in LSW mullet were tall columnar with short microvilli but in HSW the microvilli were highly distorted or swollen, mitochondria were abundant and distributed throughout the cell and confined to the basal part in LSW. P3 cells in HSW fish had large subnuclear vacuoles and large clear area containing degenerated membranous structures, may be a process of decreasing the functional cells as a result of high salinity adaptation. A second cell type (ciliated cells) was identified in-between the main cells. They were small, triangular with elongated nucleus. Cilia, basal bodies and some mitochondria were seen. The mitochondria were more numerous in LSW than HSW mullet. A third type (dark cells) was more abundant in HSW than LSW. They were characterized by electron dense cytoplasm, small dense mitochondria and basal cytoplasmic processes that extend below the neighboring light cells. The distal convoluted tubules were lined by cuboidal cells that having no brush border. The basal and lateral enfolding was extremely extensive associated with elongated and large mitochondria especially in LSW mullet. In contrast, the collecting tubule cells were tall columnar with short microvilli that were particularly distorted and irregular in HSW mullet. These tubules were surrounded with a thin basement membrane, smooth muscle cell and collagen fibers. In conclusion, the difference in the ultrastructural appearance of different types of cells that forming the renal tubules may reflects their adaptations to LSW or HSW habitat.
Ultrastructue, Urineferous Tubules, Mugil Capito, Different Salinity Habitat