The potential of biogas production using fish waste (FW) and its effect on greenhouse gas (GHG) reduction and on energy production were evaluated on this research. FW was co-digested with anaerobic sewage sludge (SS). The FW was collected in the city of Bragan?a, northern Brazil, in which the fish industry is the main activity with a FW production of approximately 9,000 kg?day-1. The experimental part included five SS/FW ratios, and in two experiments hydrogen was added. The experiments were carried out for 30 days and the effect on the cumulative biogas and methane yields were analyzed. The GHG reduction was estimated using the amount of FW not discarded in the Bragan?a open dump; and the electricity generation was calculated using the methane yield. Besides, two kinetic models were performed. The results presented a GHG reduction of 1,619 tons of CO2e and an electricity production of 372 to 956 MWh?year-1. The analysis of variance indicated that the methane production was highly dependent on the SS/FW ratios which ranged from 76 to 138 mL?gvs-1. Finally, this research showed the benefit of using FW to generate biogas and electricity while reducing GHG emissions in a city where there is no energy project.