We investigated the spatial patterns of distribution and abundance of native (migratory and sedentary) and non-native fish species in a cascade reservoir system located in the semiarid region of Brazil. Our hypothesis was that sedentary and non-native species would dominate the reservoirs in terms of abundance. Additionally, we expected to observe an increase in species abundance along the cascade, accompanied by changes in community composition. Sampling was conducted using gillnets in four reservoirs distributed along the longitudinal axis of the Apodi-Mossor & oacute; River. Data were analyzed using non-metric multidimensional scaling (MDS) and Generalized Additive Models for Location, Scale, and Shape (GAMLSS). A total of 13,787 individuals belonging to 22 species were captured. Mean species abundance (CPUEn) increased toward the mid-course reservoir, followed by a sharp decline in the downstream reservoir. The study hypothesis was confirmed, as sedentary species were the most abundant throughout the cascade system, while the abundance of nonnative species surpassed that of migratory fishes. The spatial variation observed in fish assemblages along the Apodi-Mossor & oacute; River appears to be associated with multiple factors, particularly reservoir size and position within the cascade.