Prochilodus magdalenae (bocachico) is a fish species native to Colombia that has suffered a marked population decline due to various anthropogenic and climate-related pressures. This study examined variations in seminal quality of males kept in captivity throughout the reproductive cycle (early season: May–July; late season: October–December). Fifteen key parameters were assessed, including sperm motility kinetics, semen volume, plasma pH, osmolarity, and total antioxidant capacity (TAC), the latter being a reliable integrative marker of sperm quality and redox balance.
Environmental variables such as air and water temperature, rainfall, and the El Niño–Southern Oscillation (ENSO: positive or neutral) were also recorded to explore their associations with TAC and other sperm traits. Principal Component Analysis (PCA) revealed a functional separation between early and late reproductive phases, with the first two components explaining 60.9% of total variance (Fig. 1). PERMANOVA confirmed highly significant differences between periods (p < 0.001).
Early-season samples showed significantly lower TAC (200.7 ± 25.0 vs. 312.4 ± 162.4 μ mol TE/100 g), total motility (96.2 ± 4.4% vs. 97.8 ± 3.4%), and sperm concentration (17,430.7 ± 1,849.6 vs. 28,956.4 ± 2,238.1 × 10⁶ Spz/mL), along with a more alkaline plasma pH (8.1 ± 0.3 vs. 6.2 ± 0.4). This early period also coincided with a positive ENSO event and elevated water temperatures (30.4 ± 1.06 °C vs. ~27 °C in the late season).
The Boruta machine learning algorithm identified five variables significantly associated with TAC (p < 0.01), led by climatic variables such as ENSO and water temperature (Fig. 2). Interestingly, early-season samples exhibited increased motility duration, speed, and velocity—a likely compensatory response to thermal stress which helps maintain reproductive capacity for short periods , potentially favored by alkaline plasma pH.
This study provides the first evidence that climate variability negatively impacts sperm quality in P. magdalenae, offering a valuable model to understand how reproductive performance, viability, and long-term persistence of neotropical fish may be affected by climate change.