Abstract
Several groups of Amazonian fishes exhibit behavioral, morphological and physiological characteristics that allow occupying hypoxic environments, despite the energetic costs of living in such harsh conditions. One of the supposed advantages of occupying hypoxic habitats would be a lower predation pressure resulting from a lower number of piscivorous fishes in those environments. We tested this hypothesis in an area of the Amazon River floodplain through gill net fishing in normoxic and hypoxic habitats. From the 103 species caught, 38 were classified as piscivores. We found no difference in the number of piscivorous species captured in hypoxic and normoxic habitats (chi2 = 0.23; p = 0.63; df = 1) but piscivorous individuals were more numerous in normoxic than in hypoxic sampling stations (chi2 = 104.4; p < 0.001; df = 1). This indicates that environments submitted to low oxygen conditions may in fact function as refuges against piscivorous fishes in the Amazonian floodplains.
Highlights
The Amazon basin covers an area of about 7,000,000 km2 and contains one of the richest freshwater fish faunas of the world (Roberts, 1972; Santos and Ferreira, 1999; Reis et al, 2003)
In várzea floodplains, dissolved oxygen is subjected to large seasonal variations, as well as daily fluxes (Schmidt, 1973; Junk, 1980; Melack and Fisher, 1983; Furch and Junk, 1997)
The aim of this study is to assess the spatial distribution of piscivorous fishes in relation to the dissolved oxygen content in central Amazonian floodplain lakes, in order to examine whether predation pressure is lower in hypoxic than in normoxic environments
Summary
The Amazon basin covers an area of about 7,000,000 km and contains one of the richest freshwater fish faunas of the world (Roberts, 1972; Santos and Ferreira, 1999; Reis et al, 2003). Fish inhabiting várzea floodplains have developed diverse morphological, physiological, and behavioral mechanisms to cope with periodically hypoxic conditions that occur, especially during the flooding season (Saint-Paul, 1984; Saint-Paul and Soares, 1987; AlmeidaVal and Hochachka, 1995; Val and Almeida-Val, 1995; Soares and Junk, 2000). These mechanisms may represent a costly trade-off to individuals both in terms of energy and time, limiting the energy invested in
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