Lipids requirement of tropical gar Atractosteus tropicus prejuveniles and juveniles was evaluated on growth, survival, chemical composition and apparent digestibility coefficient (ADC). Four semi-purified experimental diets (5, 10, 15 and 20% of lipids) were obtained with a mix of menhaden oil and soybean lecithin (2:1 ratio). Two trials were carried out, first with 600 prejuveniles of 0.5 g (35 days post-hatching, dph) for 56 days, and the second with 160 juveniles of 15 g (two-months-old) for 42 days. In the first trial, 15 (40.8 g) and 20% (40.2 g) lipid diets showed the best weight. Significant differences were obtained in condition factor (CF), daily lipid intake (DLI), hepatosomatic index (HSI), crude protein, ashes, nitrogen-free extract, moisture and ether extract between treatments. In the second trial, fish fed with the 10% lipid diet obtained the highest weight (89.1 g) compared with the other treatments. Significant differences were recorded for weight gain (WG), feed conversion ratio (FCR), specific growth rate (SGR), condition factor (CF), and lipid efficiency rate (LER). Also, significant differences were obtained in crude protein, ether extract, NFE, gross energy, apparent lipid ADC, protein ADC and dry matter ADC. The polynomial models applied to both trials indicated an optimum lipid requirement of 17% for 0.5 g juveniles and of 9% for 15.2 g juveniles.Lipid requirement of tropical gar Atractosteus tropicus juveniles was evaluated on growth, survival, chemical composition and apparent digestibility coefficient (ADC). Four semi-purified experimental diets (5, 10, 15 and 20%) were obtained with a mix of menhaden oil and soybean lecithin (2:1 ratio). Two trials were carried out, first with 0.5 g juveniles (35 days post-hatching) over 56 days, and the second with 15 g fish (two months-old) over 42 days. In the first trial, fish fed with diets of 15 and 20% lipid obtained the greatest weights (40.8 and 40.2 g respectively). Significant differences were detected in the condition factor (CF), the daily lipid intake (DLI) and the hepatosomatic index (HSI) in different treatments. For crude protein, ashes and nitrogen free extract, moisture and ether extract, significant differences were detected. In the second trial, the fish fed with the 10% lipid diet obtained the greatest weight (89.1 g). Significant differences were recorded for weight gain (WG), feed conversion rate (FCR), specific growth rate (SGR), condition factor (CF), and lipid efficiency rate (LER) in the treatments. Also significant differences were obtained in crude protein, ether extract, NFE, gross energy, apparent lipid ADC, protein ADC and dry matter ADC. The polynomial models applied to both trials indicated an optimum lipid requirement of 17% for 0.5 g juveniles and of 9% for 15.2 g juveniles