SUMMARY Forty Nile fish, Oreochromis niloticus were injected with insulin (20 IU/Kg body weight) for different periods. Single dose for 24 h and repeated doses (dose every 48 h for 30, 45 and 55 days) were used in this experiment. Body gain, condition factor (Cf), hepatosomatic index (HSI) and gut weight were calculated. Levels of total lipids, triglycerides and cholesterol were determined in serum, liver and myotomal muscle.
Also, sodium and potassium levels were estimated in both serum and muscle but inorganic phosphorus was determined only in serum. Insulin injection increased significantly body gain (P<0.05) and gut weight (P<0.01). While hepatosoma was significantly decreased (P<0.01) in insulin treated group at 30 and 45 days of the experimental periods. The prolonged administration of insulin in Oreochromis niloticus showed a continued effect on the stimulation of lipogenic in the myotomal muscle as well as in the liver triglycerides synthesis. The lowering effect of insulin on liver content of triglycerides but not in the serum. let to suggest that insulin might promote the triglyceride synthesis in liver to be removed as rapidly as synthesized to lipid stores in the body. The increasing effect of insulin on serum and muscle potassium level probably reflect role of such hormone in osmoregulation in this fish.