Aiming at finding out how arginine affects fish composition and/or the reproductive performance of young Nile tilapia (Oreochromis niloticus), the present study was carried out. A 4 X 2 factorial design experiment was conducted to evaluate 4 dietary lipid sources, namely: canola oil, CO; soybean oil, SBO; linseed oil, LO and fish oil, FO in the presence or absence of arginine (ARG) and their interaction effect on gonadal development of young Nile tilapia. Eight practical diets were formulated to be isoproteic (30% CP) and isocaloric (20 KJ/g diet), each with one of the four mentioned oils with (0.7%) or without (zero, 0) arginine supplementation. The four 0-added ARG- diets were designated as: C, S, L, F whereas the other 4 ARG-added diets were:  C^0.7, S^0.7, L^0.7, F^0.7 ,respectively. Following 2 months of feeding the whole-fish biochemical composition was determined and gonads (testis and ovary) were histologically examined. Results showed that dietary arginine supplementation had no beneficial effect on the protein content of fish but led to a decrease in the whole fish lipid content of both sexes.In the meantime, dietary ARG addition by 0.7% had counteracted the retardation effect on maturity stages caused by feeding fish vegetable oils. These results suggested a general positive effect of arginine supplementation on the developmental stages of maturity in both ovaries and testes in young Nile tilapia.  Therefore, dietary arginine supplementation may be essential for normal development of gonadsof Nile tilapia when fed the tested vegetable oils for 2 months.