This study attempts to provideinformationon ultra- structureofthe gut-secretory cells of young whipfin mojarra fish, Gerres filamentosus( Cuvier, 1829)to its functionality where their habitat in a near shore species off Hurghada , Red Sea, Egypt. The gut illustrating: esophagus, stomach, four-pyloric caecae, and intestine.Under the transmission electron microscopy (TEM), revealed that cells in the epithelium of the esophagus have an unbroken apical layer and goblet cells. The lining of the esophagus display a peculiar form of surface amplification involving the formation of elongate flask-shaped invagination of the apical cytoplasm.the intestine is a relatively undifferentiated muscular tube lined with a simple columnar epithelium interspersed with goblet cells. The proximal region has a greater surface area, manifested by elongated mucosal ridges.The distal intestine mucosa is thinner and less elaborately folded and consists of columnar cells with shorter and sparser microvilli. Their supranuclear cytoplasm contains abundant clear vacuoles. Numerous endocrine cells were observed. Regional cellular ultrastructural features are correlated with digestive functions. Lipid absorption occurred throughout the intestine in all sizes of examined fish specimens.