The objective of this study was to explore the utilization of tambaqui (Colossoma macropomum) viscera in silage (VS), as a novel feed ingredient, to bring additional revenue to the entire fish farming industry. Different silage processes were evaluated, and the best ingreident was the fermented silage. It was manufactured with 79.8% ground tambaqui viscera (w/w), 15% sugar cane molasses, 5% expired whole yogurt (as a source of lactic acid bacteria), and 0.25% sorbic acid as an antifungal agent. A comprehensive assessment of VS nutrient composition, fatty acid and amino acid profiles, as well as the apparent digestibility coefficients (ADC) of nutrients and energy for juvenile tambaqui, was performed to select the best silage method. Following the characterization of VS , five experimental diets were formulated with graded levels of VS inclusion (0%, 5%, 10%, 15%, and 20%) to assess the physical quality of the feed, and the production performance of tambaqui during a comparative feeding trial. Juvenile tambaqui (~22.6 g initial weight) were randomly distributed among 20 fiberglass tanks (700 L ; 21 fish/tank), and fish were fed four times daily until apparent satiation for 13-week period. The silage presents 45.8% dry matter, 24 % lipids, and 24% crude protein, and leucine and lysine were found in high concentrations when compared to other essential amino acids. Fish viscera silage contained levels 5.4 mg of eicosapentaenoic acid/g of lipids to 1.7 mg of docosahexaenoic acid/ g of lipids. The ADC for protein, lipids, and gross energy were 88.3%, 94.5%, and 85.1%, respectively. Pellets containing higher levels of VS exhibited reduced rates of expansion and floatability. Nevertheless, fish in all experimental groups displayed similar growth, achieving a remarkable 500% increase in weight relative to their initial weight. The average apparent feed conversion rate was 1.43, the protein efficiency rate was 2.28%, and the relative growth rate reached 1.79% per day. Fish fed 20% VS showed an increase in plasma cholesterol levels; however, it remained within the range for healthy tambaqui. Incorporating viscera silage into the diets of juvenile tambaqui led to a decrease in the activity of the alanine aminotransferase enzyme, which confirms normal liver functions. The production cost of the diets averaged US$ 0.94/kg and did not significantly impact the economic efficiency indicators. Converting fish viscera into silage results in an energy-rich ingredient suitable for aquafeeds, and readily digestible by juvenile tambaqui. In conclusion, it is feasible to incorporate up to 20% of fermented viscera silage into the diets of juvenile tambaqui without adversely affecting their growth and overall health.