Abstract: Salvinia molesta is an aquatic weed that can be found in swamps and lakes. The Central Java government is very interested in overcoming the infestation of Lake Rawa Pening by this aquatic weed. The present research was conducted from May until June 2014 at the Livestock and Poultry Laboratory of the Faculty of Animal and Agricultural Sciences of Diponegoro University in Semarang, Indonesia. The feed sample analysis was obtained from the Agricultural Extension College (STPP) of Magelang, Central Java. For this trial a flock of eighty Pengging ducks 4-week-old (male ducks) with an initial average weight of 734.25±0.52 g were used as the research subjects. Salvinia molesta was obtained from Lake Rawa Pening, and Aspergillus niger was obtained from the Agricultural Extension College (STTP Magelang). This research was carried out in two phases: the first phase consisted of the preparation, and the second phase consisted of the start, maintenance and completion of the study. A feed ration that contained fermented Salvinia molesta was used in the second phase. The ration composition of the starter and finisher periods was arranged with iso protein and energy. The addition of 15% Salvinia molesta to the local duck ration resulted in an increase in the body weight and feed conversion ratio (FCR), as well as increasing the income over feed cost (IOFC) by approximately IDR 2,468.65; this was the most efficient ration compared with the controlled ration and other rations.