The present study was performed to investigate the effects of vitamin A (VA) on tail fin regeneration of the teleost fish, Oreochromis niloticus. Following amputation, the tail fin undergoes a regenerative process which leads to an apparently faithful replacement, both in shape and size of the missing part. However, analysis of the fin skeleton of whole mount preparations of normal (unamputated), control, and treated tail fins revealed that, fin regenerates were not perfect copies of the missing part, and that the distance and the number of ray segments between the amputation plane and the first dichotomy were higher in treated tail fins than in control and unamputated fins. This suggests that VA can affect patterning formation of the regenerating tail fin. Vitamin A has morphogenetic effects on the regenerating fin by increasing the number of ray segments as well as it exhibits a marked reduction in the amount of tissue between rays that leads to fusion of adjacent rays.