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

Area of Science:

• Ecology
• Ichthyology
• Environmental Science

Background:

• Aquatic ecosystems in the Amazon are vital biodiversity hotspots.
• Understanding fish assemblage dynamics is crucial for conservation.
• Environmental factors and diel cycles can significantly impact aquatic life.

Purpose of the Study:

• To investigate the influence of daily cycles and local environmental factors on fish assemblages in an Amazonian terra firme stream.
• To analyze how species richness, abundance, and composition are affected by environmental variables and time of day.

Main Methods:

• Fish were collected using sieves and hand-nets over three days during the rainy season.
• Local environmental variables (temperature, pH, dissolved oxygen) were measured concurrently.
• Statistical analyses included Generalized Linear Models, PERMANOVA, and Redundancy Analysis.

Main Results:

• A total of 18 fish species and 271 individuals were collected, with variations between day and night.
• Dissolved oxygen (DO) positively influenced fish species richness and abundance.
• Fish assemblage composition differed significantly between daily cycles and was associated with temperature, pH, and DO.

Conclusions:

• Local environmental conditions and daily cycles are key predictors of fish assemblage structure in Amazonian streams.
• Temporal organization of stream fish assemblages is critical for effective conservation planning.
• These findings emphasize the need to consider diel variations and environmental parameters in aquatic ecosystem management.