Daily cycle and environmental factors influence fish assemblage structure in an Amazonian conservation unit

We investigated the influence of daily cycle cycleand local environmental factors on fish assemblages in a terra firme stream in southwestern Amazonia during the rainy season. We collected fish by using sieves and hand-nets over three days and local environmental variables were measured throughout the collection period as well. We employed Generalized Linear Models to examine the impact of daily cycle and local environmental variables on fish species richness and abundance. We used PERMANOVA to assess changes in fish assemblage composition and Redundancy Analysis to understand variations in fish species composition in response to daily cycle and local environmental factors. We collected 18 species and 271 individuals, 111 at night and 160 during the day. Dissolved oxygen (DO) had a positive influence on species richness and abundance and species composition differed between daily cycles. Redundancy Analysis revealed associations between fish species composition, environmental variables (temperature, pH and DO), and daily cycle. These findings underscore the significance of the local environment and daily cycle in predicting variations in fish assemblage structure in Amazonian streams. Understanding how stream fish assemblages are organized temporally is important for devising effective conservation strategies in a region facing increasing human pressures on aquatic ecosystems.