¿Where do migratory fish spawn in a neotropical Andean basin regulated by dams?

Area of Science:

• Ichthyology and Aquatic Ecology
• Riverine Ecosystems
• Conservation Biology

Background:

• Spawning sites are vital for fish population persistence.
• The Nechí River is a key spawning area for potamodromous species within the Magdalena River basin.
• Dam construction poses a significant threat to these critical habitats.

Purpose of the Study:

• To assess the significance of the Nechí River as a spawning site for potamodromous fish.
• To understand the distribution and density of ichthyoplankton in relation to environmental factors.
• To evaluate the impact of hydroelectric development on fish reproduction.

Main Methods:

• Ichthyoplankton sampling during the transition from low-water to high-water season (2018-2019) at seven sites.
• Identification and density calculation of larval and post-larval fish stages.
• Analysis of spatial and temporal variations in ichthyoplankton abundance.
• Correlation analysis between ichthyoplankton presence and turbined water volume.

Main Results:

• Average ichthyoplankton density was 42.4 individuals/10m³.
• Seven migratory fish species and two additional taxa were identified, with *Prochilodus magdalenae*, *Megaleporinus muyscorum*, and *Pseudoplatystoma magdaleniatum* being most abundant.
• Peak larval density of potamodromous species occurred in the early high-water season of 2019.
• Significant differences in embryo and vitelline larvae frequency were linked to sampling sites, high-water seasons, and post-larval density.
• Average drift distance from spawning areas was approximately 52.1 km.
• A positive association was observed between turbined water volume and ichthyoplankton presence at the Porce River site downstream of the Porce III Hydroelectric Plant.

Conclusions:

• The Nechí River is confirmed as an important spawning site for potamodromous fish.
• Ichthyoplankton densities appear to increase with distance from the Porce III dam.
• The presence of floodplains is crucial for supporting higher ichthyoplankton densities, suggesting a need for habitat conservation in dam-impacted river systems.