Structure of the ichthyofauna of adventitious streams in the South Pantanal

Virginia S Uieda,César Y Fujihara

doi:10.1590/1678-4766e2018019

Abstract

ABSTRACT: The ichthyofauna of the Taquari River, one of the main tributaries of the South Pantanal, has been studied since the 1970s; however, there is a gap on the studies about the ichthyofauna present on the small adventitious streams of this highly dendritic system. These streams are small tributaries that flow directly into large rivers (mainstem), at least three orders greater in magnitude. The aim of this study was to analyze the structure of the ichthyofauna of five adventitious streams of the Upper Taquari River, South Pantanal, evaluating its temporal variation (dry and wet season) and the relation to the habitat characteristics and the conservation of the streams. Thirty-seven species were collected, from which 14 are exclusive to the Paraguay River basin, one species [Apteronotus albifrons (Linnaeus, 1766)] could represent a new record for this basin, and six species need taxonomic confirmation. The analysis indicated only the existence of spatial variation in the ichthyofauna structure of the streams sampled, with the similarity patterns related to the distance between the streams and to their conditions of conservation. The stream with greater size and preserved riparian forest was the one with the highest values of fish diversity and evenness. On the other hand, the stream with the smallest percentage of riparian forest and highest proximity to urban area presented the lowest diversity. The small size of these adventitious systems should serve as protection against large predators, which have their access to those areas hampered by their own size. Otherwise, the mainstem may also act as source of dispersal of small-bodied schooling fishes to the adventitious streams, where the greater heterogeneity of habitats and the presence of riparian vegetation should offer shelter and food supply for small species.

Highlights

Thomas & Hayes (2006) examined the fish community and habitat structure of one fifth-order mainstem, two secondorder adventitious tributaries to the mainstem, and three second-order headwater streams and verified that fish species richness generally increased with increasing stream order and was similar but higher in the adventitious streams than in the headwater streams
There is a gap on the studies about the ichthyofauna present on the small adventitious streams of this highly dendritic system of the Upper Taquari River basin, represented by species dependent on the stream conditions of conservation, with potential occurrence of endemism, and that still needs more studies (Froehlich et al, 2017)
Parameters calculated for the fish fauna sampled in five streams of Taquari River basin Brazil during the dry (D) and wet season (W)

Summary

Introduction

The distribution of the ichthyofauna in rivers with wetland can be analyzed in two distinct compartments, the plateau region with lotic environments and the floodplain region where the flood pulse exerts a strong influence on the ecological processes (Willink et al, 2000; Galdino et al, 2006) In this complex integrated system, little emphasis has been placed on the study of adventitious streams or adjacent small rivers. Adventitious streams are small tributaries (1st to 3rd order) that flow directly into large rivers (mainstem) at least three orders greater in magnitude (Gorman, 1986) In these environments, species composition may vary according to watershed structure, species potential of migration and environmental conditions (Hitt & Angermeier, 2006). There is a gap on the studies about the ichthyofauna present on the small adventitious streams of this highly dendritic system of the Upper Taquari River basin, represented by species dependent on the stream conditions of conservation, with potential occurrence of endemism, and that still needs more studies (Froehlich et al, 2017)

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