Influence of rainfall, hydrological fluctuations, and lunar phase on spawning migration timing of the Neotropical fish Prochilodus costatus

Abstract

The arrival of the rains and the hydrological changes they cause are essential in the reproductive cycle of Neotropical migratory fishes, but their association with the onset of migration is still poorly understood. This study aimed to determine the role played by rainfall, hydrological changes, and the lunar cycle as triggers for migration of Prochilodus costatus (Prochilodontidae) in the upper São Francisco River, Brazil. In total, 132 individuals were fitted with radiotelemetry transmitters over three consecutive spawning seasons. Spawning migration began with the onset of the rains from late September to mid-December. Individuals exhibited a strong preference for initiating migration at the beginning of the rainy season, when river discharge is low, in days with positive changes in water level, and at times of new or waxing moon. The fraction of the population that initiates migration each year appears to be dependent on rainfall, indicating that P. costatus may be a partial migrant. The results show that P. costatus and, possibly, other migratory Neotropical fish, rely on different but interconnected environmental cues to trigger their spawning migration, ensuring that individuals migrate in time to reach their spawning grounds and find appropriate environmental conditions for spawning.