Feeding ecology of Serrapinnus notomelas (Characiformes: Cheirodontinae) in small forest streams in the Machado River basin, Rondônia, Brazil

ABSTRACT Studies on the trophic structure of fish give information on species autoecology and their role in the ecosystem. The aims of this study were to characterize the diet of Serrapinnus notomelas in small streams of the River Machado basin and to assess the effect of rainfall seasonality. Fish were collected bimonthly from July 2013 to May 2014 with seine nets and hand nets. The length of each specimen was measured to identify category classes. There were also measured the fullness index and volume of each ingested item, and these data were combined to obtain an alimentary index. We used ANOVA and Kruskal-Wallis to test for differences between length classes and fullness index, Chi-squared tests to detect seasonal differences in origin of food items and non-metric multidimensional scaling analysis to examine temporal variation in diet. We found that most of the specimens were longer than 20 mm, showing a polymodal distribution. In both seasons stomachs of most fish were full. Serrapinnus notomelas feeds on items of plant and animal origin. A higher consumption of aquatic macrophytes and algae was observed, suggesting omnivorous feeding behavior with a tendency to herbivory. Items of plant and autochthonous origin were consumed more than other items in both seasons, and consumption of animal and autochthonous items varied between seasons. These results reinforce the idea that S. notomelas show trophic plasticity between seasons.