ABSTRACT The objective of this study was to determine the digestible phosphorus requirement in rations for tambaqui fingerlings (Colossoma macropomum). 900 fingerlings (0.51 ± 0.06 g) were used in a completely randomized design with six treatments, five replicates, and thirty fish per experimental unit. The treatments consisted of six diets with different digestible phosphorus levels (0.12, 0.33, 0.54, 0.75, 0.95, and 1.16%). The fish were fed six times a day, for 63 days. Performance, feed efficiency, and the daily protein, fat, ash, and phosphorus deposition rates of fish were evaluated. The treatments did not influence the feed intake. The elevation of phosphorus levels increased the digestible phosphorus intake linearly, and improved of quadratic form the weight gain, specific growth rate, feed:gain ratio, protein efficiency for weight gain, and daily protein, fat, ash, and phosphorus depositions up to the estimated levels of 0.64, 0.66, 0.70, 0.70, 0.62, 0.62, 0.70, 0.71%, respectively. The phosphorus efficiency for weight gain worsened with the elevation of phosphorus levels. The recommendation of digestible phosphorus level in rations for tambaqui fingerlings to optimize weight gain and body phosphorus deposition is 0.71%, which corresponds to the estimated level of 1.04% total phosphorus.