The effect of L-carnitine supplement on the growth performance of Nile tilapia (Oreochromis niloticus) fingerlings was investigated. One group was fed normal commercial grow-out feed (the control group) while the other group was given feed containing 500 mg kg L-carnitine. The addition of carnitine (the second group) had a positive effect on growth (7.9% higher than the control group). According to the final results, the carnitine-supplemented group had greater final weights (151.86 +/- 27.19 g) than those of the control group (141.80 +/- 24.83 g) (P < 0.05). This enhancement in growth was not due to a better feed conversion ratio (1.16 +/- 0.31 vs. 1.20 +/- 0.28) (P > 0.05). At the end of the feeding period of 90 days, 9.67% less feed containing L-carnitine was consumed by fish as compared to the control diet. The carnitine-supplemented diet promoted rapid growth (7.77% more than the control diet). The final total weight of the carnitine-fed group was also greater (10.022 +/- 0.83 kg m(-3)) than that of the control group (8.933 +/- 0.91 kg m(-3)) (P > 0.05).