Reproductive intensity of fish assemblages from streams of the Contas river basin, State of Bahia, Northeastern...

Information about the reproductive biology of fish assemblages is limited, particularly for coastal basins in Northeast Brazil. However, this information is crucial for understanding species' life histories and informing conservation strategies and management actions. The scarcity of studies on the reproductive patterns of stream fish highlights a significant research gap, as this knowledge is essential for the effective conservation of these ecosystems. This study aimed to assess the reproductive intensity of fish assemblages from streams that are part of two drainages of the Contas River basin (Upper Contas and Gongogi River drainages), which are located in two distinct biomes (Caatinga and Atlantic Forest, respectively) in the Northeast Brazil. The fish were collected between November 2012 and November 2013 in four quarterly expeditions that encompassed one seasonal cycle. The captures were conducted by electric fishing in 18 sampling sites, nine in the Upper Contas River drainage and nine in the Gongogi River drainage. We obtained the reproductive intensity index (RII) of the studied assemblage, being the values compared between expeditions, drainages, and sampling sites. The highest values of RII were observed between November/December and February/March in both drainages, which demonstrated that the highest reproductive intensity was associated to the rainy season. In the Upper Contas River streams, the reproductive peak intensity seems to be synchronized to the beginning of the rainy season, while in the Gongogi River drainage streams, the reproductive intensity remains high throughout the entire rainy season. Regarding spatial variation, the highest RII values were observed in smaller streams, probably associated with a more restricted species distribution in these locations. Our results indicate that the assessed streams play a crucial role in the reproduction of many fish species, as evidenced by the high reproductive intensity observed, particularly within the fish assemblage of the Upper Contas River.