Population aspects of two non-native shrimp species in a neotropical hydropower reservoir

Non-native freshwater decapods are increasingly established in neotropical freshwater ecosystems, particularly in hydropower reservoirs. This study evaluated the mechanisms underlying the coexistence of two non-native shrimp species in the Furnas hydropower reservoir. Sampling was conducted at three reservoir sites using baited shrimp traps and gillnets. We analyzed population attributes, diel activity, and trophic interactions based on the occurrence of shrimp in predatory fish diets. Results showed that M. pantanalense was numerically dominant, characterized by smaller body size, fewer non-ovigerous females, and predominantly diurnal activity. M. amazonicum displayed contrasting population and behavioral traits, including larger body size, higher relative biomass, a predominance of ovigerous females, and nocturnal activity. These contrasting population and behavioral patterns indicate coexistence mediated by reproductive and temporal niche differentiation. Shrimp were frequently detected in the stomach contents of predatory fish species such as Trachelyopterus galeatus and Cichla piquiti, whereas Pimelodus maculatus exhibited a generalist diet with low occurrence of these crustaceans. This study advances understanding of the ecological mechanisms underlying the coexistence of non-native freshwater decapods in reservoir ecosystems, highlighting the need to incorporate invasive crustaceans into monitoring and management programs for neotropical reservoirs.