A long-term study on the larval distribution of the migratory fish Salminus brasiliensis (Characiformes: Bryconidae) in a dam-free section of the Parana River, Brazil

The objective of this study was to use larval density data to investigate the temporal reproductive pattern and use of different biotopes of the Parana River as areas of reproduction and the initial development of the migratory fish Salminus brasiliensis. During 15 reproductive periods (October to March) between 2001 and 2019, three biotopes (channel, tributary, and lake) of the upper Parana River floodplain were sampled using conical-cylindrical plankton nets equipped with a flowmeter. The highest larvae densities were recorded between October and January, with a predominance of the pre-flexion and flexion stages captured mainly in the Parana River channel. Larvae in the yolk-sac stage were most common in the tributaries. Temperature, pH, and rainfall were the main variables that influenced larval density. Our results showed that the reproduction of S. brasiliensis may have failed during a few reproductive periods and that the species uses different biotopes of the Parana River for spawning and development, i.e., the tributaries and the river channels and lakes, respectively. Thus, providing conditions enabling a smooth migration to the tributaries for spawning as well as ensuring safe development in the river channels and lakes during their reproductive periods could help conserve this vulnerable species. Moreover, actions aimed at recovering the stocks of the species depend on the conservation of different floodplain environments and the maintenance of their original characteristics and on policies aimed to conserve the species, such as the prohibition of fishing.

Automated summary

The study investigated the temporal reproductive pattern and use of different biotopes as areas of reproduction and initial development by analyzing larval density data of Salminus brasiliensis in the Parana River. The results showed that larvae in different stages were found in different biotopes, with pre-flexion and flexion stages mainly in the Parana River channel, and yolk-sac stage in the tributaries. Temperature, pH, and rainfall were found to be the main variables influencing larval density. Conservation efforts should focus on providing suitable conditions for migration and development in different biotopes of the Parana River.