Agricultural byproducts, often discarded, possess significant nutritional value and technological potential. This study investigates the efficacy of ethanolic-water extracts from avocado (Persea americana Mill.) byproducts, obtained with minimal solvent use through optimized extraction, in enhancing the stability of mechanically separated meat-tambaqui (Colossoma macropomum) burgers, a high-fat Amazonian fish. 2000 ppm of avocado seed and peel extract were applied in shelf-life tests conducted under refrigeration and freezing conditions to evaluate the stability of the burgers. The results demonstrated that the bioactive compounds from avocado byproducts resulted in lower TBARS values, indicating strong antioxidant properties, reduced formation of volatile nitrogen compounds, and color maintenance than sodium erythorbate. Monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) were preserved using bioactive ethanolic-water extracts, and the protein content was improved compared to the control, enhancing nutritional quality. This study highlights the potential of using agri-food byproducts, especially for application in highly perishable items such as fish, promoting the development of clean label products, thus supporting a more efficient and environmentally friendly food industry focusing on the circular economy.