LIMNOLOGICAL CHARACTERISTICS EFFECT OF THE TAPAJÓS AND AMAZON RIVERS ABOUT VARIABILITY IN THE COMPOSITION AND ABUNDANCE OF FISH LARVAE (PARÁ-BRAZIL)

Abstract

Variations in species composition and the relative abundance of fish larvae were investigated during the 2019 flood at six sampling stations along the discharge zone and confluence of the Tapajós River with the low stretch of the Amazon River. The limnological characteristics indicated (as expected) the presence of two different types of water bodies outlining different sections and a confluence limit between the Tapajós River (tributary of clear waters) and the Amazon River (white waters). The region supports an ichthyoplankton community divided into species with pelagic eggs and fish larvae distributed in seven (07) orders. Compared to the number of larvae, the density of fish eggs was very low. The highest relative abundances and larvae richness were recorded in the Amazon River, which showed high values of electrical conductivity and turbidity when compared to the Tapajós River. The ichthyoplankton fauna can be classified into two distinct groups: clear and white waters. These two groups initially result from the spawning preferences displayed by the different species. Both assemblages held predictable phenology, with a rate of migratory Characiformes and Siluriformes commercial interest dominating the white-water River (Amazonas), followed by Clupeiformes in the clear waters of the Tapajós River. The frequency distribution of the developmental stages suggests that the larvae of Clupeiformes are not effectively retained in the floodplains of the Tapajós River and can be drifted to the floodplain areas downstream of the confluence zone. The sections analyzed in the confluence zone cannot be considered relevant spawning and breeding sites for any fish found in the area, however, the results indicated that the section studied is used as an important dispersal and larval transport site.