Cell renewal in the gills of the fish Barbus conchonius

This radioautographic study established that the epithelial cells of the teleost gill have the cell division and cell migration patterns characteristic of a cell renewal system. [3H]Thymidine was injected into the small tropical fish Barbus conchonius, where it became incorporated into the newly synthesized DNA of dividing cells. Three fish were sacrificed at each of the following postinjection time intervals: 1, 12, 24, and 36 h. At 1 h, labeled nuclei were found only at the base of the gill filament, near the gill arch. At each successive time interval, labeled nuclei were found further out along the length of the gill filament. At later stages, labeled nuclei were also seen at the tips of the lamellae which project perpendicularly from the filaments. The number of labeled nuclei at the point of origin steadily declined with time. These data demonstrate that gill epithelial cells originate at the base of the gill arch and migrate both outward along the filament and upward along the lamellae. This pattern of cell division and cell migration demonstrates that the gill epithelium is a cell renewal system.