Analysis of the stomach contents of Arapaima gigas in the Cautário River Basin, Rondônia, Brazil

Arapaima gigas is the largest scaled freshwater fish in the world and can grow to more than 3 meters in length and exceed 252 kg. This species naturally inhabits the flooded areas of the Amazon basin, but it has been found outside this region as a result of intentional or accidental human actions. In this study, we analyzed the items consumed by the A. gigas distributed in the Cautário River, a tributary of the Guaporé River Basin (Rondônia, Brazil), in which pirarucu is not native and requires actions for its eradication. Experimental fisheries were conducted from August 2023 to September 2024. A total of 128 A. gigas were captured (ranging from 1.16 to 2.26 m, with a mean of 1.76 ± 0.31 m, and weight of 24.70 to 111.60 kg, with a mean of 52.37 ± 22.54 kg) and had their stomachs analyzed. It was observed that 104 stomachs were full and 24 were empty. In the stomachs, five categories of food items were classified: fish and fish remains, plant material, debris, crustaceans, and worms. The items with the highest absolute frequency were plant materials (82), fish and fish remain (51), worms (32), and crustaceans (1). It was concluded that the A. gigas of the Cautário River Basin feed mainly on fish, but with a large participation in the diet of plant materials, which may be an indication of involuntary ingestion due to the animal’s voracity or possible onset of food shortages in the study region.