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The Morphological Structure of Mitochondrion-rich Cells in the Gills of Juveniles of the Milkfish (Chanos chanos) and Its Changes in Various Salinities
Ou Youjun1*, Lin Xianzhi1,2, Li Jiaer1, Wen Jiufu1
1Key Lab. of South China Sea Fishery Resources Exploitation & Utilization, Ministry of Agriculture,South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510300, China;
2College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China
Abstract: The distribution and changes of the mitochondrion-rich cells in gills and changes in gills of juveniles of seawater-acclimated milkfish Chanos chanos under different salinities (0， 10， 20， 27， 35 g/L) were studied by light micrograph， transmission electron micrograph and scanning electron micrograph. Mitochondrionrich cells with large number of mitochondria and large nucleus were oval or ovoid in gills. Two types of mitochondrion-rich cells in gills of juveniles of milkfish were observed when acclimated to various salinities: type A mitochondrion-rich cells with apical crypts and larger mitochondria; type B mitochondrion-rich cell which was a single cell with smaller mitochondria. With the reduction of salinity， the number and size of mitochondrion rich cells and mitochondria were reduced， electron density was decreased and the apical opening of mitochondria was narrower or closed. When milkfishes were transferred to fresh water， hypertrophy was observed on branchial lamellae， and type B mitochondrion-rich cells with large area apical membrane appeared as a flat or wavy disk with a mesh-like structure on its surface were observed on branchial lamellae. The results indicated that type A mitochondrion-rich cells would be rich and well developmented in hypertonic environment. Type B mitochondrionrich cells would be rich in hypotonic environment. So， type A and type B mitochondrion-rich cells were considered to be seawater-acclimation type and freshwater-acclimation type respectively， for their structural characteristics adapted in ion intake and secretion functions. Meanwhile， the existing of different types of mitochondrion-rich cells in gills can make euryhaline marine teleost adapt to a wider range changes of salinities.
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