The morphology of the intestine has been studied in a species of warm
water fish, Tilapia spp., a hybrid teleost of notable economic importa
nce. Light and electron microscope results show that the intestine is
a relatively undifferentiated muscular tube lined with a simple column
ar epithelium interspersed with goblet cells. The proximal region has
a greater surface area, manifested by elongated mucosal ridges. The en
terocytes are covered apically with uniform microvilli and exhibit the
typical ultrastructural features of pinocytosis, namely extensive inv
aginations of the luminal plasma membrane and massive accumulation of
vesicles in the apical cytoplasm. The distal intestine mucosa is thinn
er and less elaborately folded and consists of columnar cells with sho
rter and sparser microvilli. Their supranuclear cytoplasm contains abu
ndant clear vacuoles. Numerous endocrine cells can also be seen. Regio
nal cellular ultrastructural features are correlated with digestive fu
nctions.