Mucous Cells in the Gills of Fresh Water Fish (Oreochromis Niloticus) and Marine Water Fish (Sparus Aurata)

The mucous cells of both species were scattered throughout the gill filament epithelium and mostly localized apically between the pavement cells. Meanwhile, very few mucous cells were rarely observed in the secondary lamellar epithelium. The mucous cells of the Sparus aurata had fine granular light acidophilic cytoplasm. While, those of Oreochromis niloticus lacked the acidophilic cytoplasm or had faintly acidophilic vacuolated cytoplasm.

Histochemically, the granules of mucous cells of Oreochromis niloticus showed strong positive reactivities with PAS as well as, alcian blue pH 1 and pH 2.5. Whereas, these granules in Sparus aurata were PAS positive but, showed a very faint or even negative reactivity with alcian blue.

Ultrastructurally, the cytoplasmic granules of the mucous cells of Oreochromis niloticus were either scattered throughout the cytoplasm or localized in the basal part of the cell and showed some variability in their electro-density. Meanwhile, the mucous granules of Sparus aurata were always distributed all over the entire cytoplasm and showed variable electro-density within the same cell and also between the adjacent mucous cells.