Under the surface: exploring the link between fish distribution and dissolved oxygen in macrophyte banks of Lake Catalão, Central Amazonia João Henrique Alliprandini da Costa, Ursulla Pereira Souza, Virginia C. D. Bernardes, Thiago M. Pereira, Helen Sadauskas-Henrique

Abstract

This study seeks to unravel the role of dissolved oxygen concentration on the distribution of ichthyofauna across 32 macrophyte banks in the Amazon River floodplains, a region that not only supports a rich diversity of fishes but is also subject to severe hypoxia. Dissolved oxygen concentrations across these macrophyte banks were sampled and correlated to the distribution and abundance of different fish families. The impact of low oxygen concentration on the sizes of individual fishes within these families was also evaluated. In addition, the study analysed how variations in dissolved oxygen influenced the nestedness and turnover components of beta diversity. Our findings indicated a relatively low range of dissolved oxygen concentration, between 0.0 mg/L and 2.7 mg/L, across the sampled locations. Certain fish families, such as Triportheidae, demonstrated a high prevalence in areas with lower dissolved oxygen concentrations, suggesting a morphological adaptation to hypoxic environments. A pattern of smaller fish sizes at lower dissolved oxygen levels was also observed, potentially indicating the use of macrophyte banks as resource and shelter hubs for juvenile fishes. A significant impact of dissolved oxygen variations on both the nestedness and turnover components of beta diversity was also identified, suggesting a substantial influence on ichthyofauna composition. These observations underline the critical importance of considering dissolved oxygen as a key determinant in species distribution in macrophyte banks studies, as well as its role in conserving the biodiversity of aquatic ecosystems.