In this study was tested the effect of betaine on the growth performance of the piauçu fish. For this, twenty-one fish (mean ± SD: body weight: 14.9 ± 1.3 g) were randomly distributed in one out of three experimental treatments (n = 7 each; 1 fish/aquarium): without betaine added in the food (control); 3.6 g betaine/Kg of food; 7.1 g betaine/Kg of food. The fish were exposed to experimental conditions for 60 days. Fish presented significant growth throughout experimentation, but no statistically significant difference was found for any parameter analyzed among the treatments, except for condition factor, which was higher in control group than betaine ones. Accordingly, it was concluded that betaine had no enhancing effect on growth of piauçu.Abbreviations: SGR -specific growth rate; FCE -food conversion efficiency; FI -food intake; K -condition factor; TGC -thermal-unit growth coefficient