Influência do oxigênio dissolvido no padrão de ocorrência e distribuição de peixes em ecossistemas aquáticos lacustres da bacia do rio Paraná.

Abstract

This study analyzed how physicochemical parameters, with an emphasis on dissolved oxygen, influence the occurrence and distribution of fish species in lacustrine environments of the upper Paraná River floodplain. Grounded in classical ecological theories, such as Law of Tolerance, the research aimed to identify species’ tolerance limits in response to environmental variation. The analysis was based on long-term data (2000 to 2018) collected from six marginal lakes across three subsystems (Paraná, Baía, and Ivinhema), evaluating variables such as water and air temperature, pH, electrical conductivity, transparency, and dissolved oxygen. Multivariate techniques were applied, including Principal Component Analysis (PCA) to summarize abiotic gradients, and Principal Coordinates Analysis (PCoA) based on species presence-absence matrices. Dissolved oxygen values were correlated with PCoA axes, and logistic regression models were used to estimate associations between species occurrences and oxygen levels. The results showed that higher oxygen concentrations were associated with greater homogeneity in fish assemblages, while hypoxic and anoxic conditions led to increased heterogeneity and favored species with adaptive strategies such as aerial respiration or physiological tolerance. Boxplots constructed for the ten species with the highest and lowest log-odds revealed variations in their occurrence ranges along the oxygen gradient, allowing classification into generalist and specialist groups. These findings highlight the role of dissolved oxygen as a key environmental filter in structuring fish communities, especially in floodplain ecosystems subject to seasonal fluctuations and extreme events. The study also provides important insights for anticipating the effects of climate change on aquatic biodiversity and supports the development of conservation strategies for tropical river systems.