The nutritional quality of tilapia fillet is characterized by low omega-3 polyunsaturated fatty acids (n-3 PUFAs). The objective of the present study was to evaluate the effect of different dietary concentrations of chia (Salvia hispanica) and flaxseed (Linum usitatissimum) meal on the omega-3 fatty acid content of tilapia (Oreochromis niloticus) fillet. Six experimental diets incorporating 5, 10, and 15% chia or flaxseed meals, respectively, were given to the fish (238.36 ± 7.61 g, initial weight) for 45 days before harvesting. The α-linolenic acid (ALA) and n-3 PUFA contents in the fillet differed significantly among diets (P < 0.05). Diets containing 15% chia or flaxseed meal had the highest concentrations of ALA (4.80 and 4.75%, respectively) and n-3 PUFA (13.65 and 15.92%, respectively). Thus, chia or flaxseed meal dietary inclusion increased the ALA and n-3 PUFA contents in the tilapia fillet. Chia or flaxseed meals are useful and potential alternatives to improve the nutritional value of O. niloticus fillets.