Distribuição e ocorrência do ictioplâncton na região de planalto do alto Rio Paraguai: uma análise comparativa entre sub-bacias

Abstract

Studies related to eggs and larvae of freshwater fish are incipient and present gaps in relation to research into the composition of assemblages, description and distribution patterns. However, we are gaining visibility, viewing it as a tool for understanding areas and periods of development, in addition to seeking information about distribution patterns. In this context, the Pantanal plateau deserves attention in relation to understanding the reproductive dynamics of fish, especially migratory species that occupy their positions on the plateau for spawning. Thus, the objective of this work is to investigate the importance of the sub-basins of the Negro and Apa rivers in the reproductive dynamics of fish species in the Pantanal, in addition to verifying the difference between the sub-basins. Sampling was carried out monthly in six locations distributed along the Negro and Apa rivers and tributaries, between October/2017 and March/2018 and October/2018 and March/2019. Collections were carried out in nictimeral cycles at intervals of 6 hours (12, 18, 0 and 6 hours) with the aid of conical-cylindrical (5mm), mesh planning networks (5mm) at a time interval of 3 minutes. Spatial variation in egg density was observed only for the Negro river sub-bacteria, with higher densities in the Rico and Peixe streams, while, for larvae, the variation was evident in the Apa river sub-bacteria, with the Apa river showing high values. Temporally, variation in egg density was evident in the two sub-basins, with higher densities in the months of October and November of the second cycle. For larvae, there were no temporal variations between the subbasins, however, the months of November in both cycles were more representative. Dissimilarity was observed between the sub-basins in relation to the stages of development of eggs and larvae, with the Rico and Peixe streams (sub-basin of the Rio Negro), which confirmed all stages of egg development and the highest densities of larvae. 20 genera and/or species of fish were recorded and 2 more taxa were identified to order. Among the taxa identified, eight (8) belong to the guild of long-distance migrants, with emphasis on the Pimelodidae family and the species Hemisorubim platyrhynchos and Prochilodus lineatus present in both sub-basins. Migrators preferred the Apa River sub-basin, however, in the Negro River sub-basin, unidentified taxa were abundant, especially the Pimelodidae family, which includes migrants. Finally, the Negro River sub-basin presents a different pattern from the Apa River sub-basin, with variation in spawning locations, including greater representation in embryonic and larval development projects, while migrators prefer the Apa River. In this way, these sub-basins present important tributaries on the plateau, which promise areas of development and development for the fish that will be recruited in the Pantanal.