The aim of this study was to evaluate the influence of bulk density of the pellet diet on feeding and aggressiveness , as well as the production performance and homogeneity of the batch of tambaqui juveniles. To manufacture the experimental diets, the single screw extruder settings were adjusted to produce pellets (equal diet formulation) with different bulk densities: high-density ( HD), medium-density (MD), and low-density (LD). The study was divided into three trials . Trial 1 : assessment of the physical quality of pellets: bulk density (BD), floatability (F), expansion (E), water solubility index (WSI), water absorvation index (WAI), pellet durability index (PDI), water stability (WS), and sinking velocity (SV) . Trial 2: 48 fish were used to assess the aggressiveness of tambaqui juveniles when offered the experimental pellets. Fish were distributed in 12 aquariums (55L; n=4; 4 fish/aquarium) in a completely randomized design with three treatments (HD, MD, and LD ). For the behavioral interactions analysis, fish were recorded for 3 days, for 5 minutes after feeding, with a total of 360 minutes of observation. Ethograms of feeding behavior and aggressive interaction were elaborated and used to quantify the frequency of the respective behavioral units. To investigate the influence of bulk density on production performance (Trial 3), 225 tambaqui juveniles were equally distributed in 15 circular polyethylene tanks (260 L) , in a completely randomized design using the same dietary treatments (n=5, 15 fish/tank). Fish were fed four times a day with 3% of biomass for 9 weeks . In trial 1, all variables were significantly affected by the density of the pellets , except for WSI and WAI. An inverse relationship between E and BD was observed, in which p ellets with higher E presented lower BD. LD presented 75.33% of F , and pellets from MD and HD sank as soon as they reached the water, with sinking velocity of 3.22 ± 0.40 and 7.37 ± 0.94 cm/s, respectively. PDI was lower for LD diets, with 99.69 ± 0.03, due to the increase in E, which results in pellets with thinner walls and less resistance to mechanical stress. In trial 2, the time of feed consumption of fish fed LD was longer, totaling 8.7 ± 2.8 minutes. However, HD and MD were similar, with 0.2 ± 2.4 and 0.2 ± 3.9 min, respectively. It is likely that the physical characteristic of the LD of floating in static water, demotivated fish to fed with the same motivation as the fish fed HD and MD, which immediately sa nk when reaching the water. However, f ish fed MD presented higher aggressiveness and social instability in relation to fish fed HD and LD pellets . The longer period that the feed pellets stay in the water column, more competition is displayed by the tambaqui while feeding . Tambaqui from trial 3, had higher feed intake when offered HD and MD pellets when compared to the fish fed LD . Despite no significant differences were observed for the weight gain data, fish fed with HD presented lower variance in total weight (15.9 % of the coefficient of variation ). HD pellet is suitable for feeding tambaqui juveniles, resulting in a more stable social hierarchy with lower aggressiveness and more homogeneous batch of fish.