The aquatic biota of the Amazon is subject to considerable daily and seasonal fluctuations in its environment. The ability to adapt to changes in the environment, such as increased water temperatures, is essential for the survival and physiological performance of these organisms. The anticipated rise in temperature and CO 2 levels, projected to reach 6 °C and 50% above current levels by the end of the century, respectively, re...

Amphibian populations are declining globally due to anthropogenic stressors such as climate change and environmental contamination. In Amazonia, where aquatic species already endure conditions near their thermal thresholds, the combined effects of rising temperatures and pesticide exposure pose a threat to their survival and physiological stability. Here, we evaluated the isolated and interactive impacts of elevated temperatur...

This paper provides a platform for the following studies within this Special Issue. ‘Ecophysiology of fishes in the two great tributaries of the Amazon in the Anthropocene’. It documents the water quality conditions and accompanying zooplankton community structure and biomass relative to fish health in the Rio Negro and Rio Solimões during the extreme drought of 2023. Our goals were to document conditions, compare them with hi...

In the Amazon basin, climate change is increasing water temperatures and CO₂ concentrations, which intensify environmental stressors for fish by increasing natural thermal regimes, reducing dissolved oxygen and pH levels. Extreme droughts, such as those recorded in 2023 and the new record set in 2024, have exacerbated these conditions and have led to widespread fish mortality. Amazonian rivers, which are characterized by contr...

The annual flood pulse is a defining feature of Amazonian floodplain lakes, creating a highly variable environment that influences resource availability, such as food and habitat. These cyclical changes necessitate a high degree of adaptability among fish species, many of which have evolved specialized strategies to cope with the fluctuating conditions. In 2023, the Amazon basin experienced a record‐breaking drought event, lea...

Microplastics (MPs) are frequently detected in the gastrointestinal tracts of aquatic organisms worldwide. We studied the contamination with plastic in an aquatic environment and in the gastrointestinal tracts of fish in two Amazonian rivers waters, Rio Negro and Rio Solimões. The research was conducted in November/December 2023 during the low water season in a year of drastically decreased water level. We evaluated the abunda...

The Amazonian loricariid fish Pterygoplichthys gibbiceps, from the Rio Negro, and Pterygoplichthys pardalis, from the Rio Solimões, are facultative air‐breathers that can use the stomach as an air‐breathing organ. Measurement of oxygen uptake under progressive aquatic hypoxia revealed a relatively high hypoxia resistance of both species. In both species, air‐breathing was initiated at aquatic PO 2 values below 3 kPa. In hypoxi...

Siluriform fishes collected from the Rio Negro and Rio Solimões proved to be highly resistant to aquatic hypoxia. In all four species analysed in this study, aquatic oxygen consumption significantly decreased from normoxic levels at water PO 2 values near 1 kPa. Air‐breathing activity was observed only in Sturisoma sp. (Rio Negro). In this species, under severe hypoxia, oxygen uptake from the air dominated, but total oxygen up...

The tambaqui ( Colossoma macropomum , G. Cuvier 1818) thrives both in the ion‐poor waters of the Amazon and in commercial aquaculture. In both, environmental conditions can be harsh due to low ion levels, occasional high salt challenges (in aquaculture), low pH, extreme PO 2 levels (hypoxia and hyperoxia), high PCO 2 levels (hypercapnia), high ammonia levels (in aquaculture), and high and low temperatures. Ion transport across...

Increases in anthropogenic activities in the Amazon have led to pollution from trace metals, including copper. Dissolved organic carbon (DOC) is known to protect against metal toxicity and ionoregulatory disturbances in Amazonian fish, particularly at low pH. However, little is known about the effects of DOC and trace metals, such as copper, on the branchial water transport pathways. Water moves across the gills of fish throug...

This study aimed to investigate how exposure to elevated water temperature and metal concentration jointly affect the physiology of Amazonian fish. Aboard a research vessel in the Amazon, we evaluated the effects of water temperature (river T°C at 31.5°C and a + 4°C increase to 35.5°C) and of 3‐h copper (Cu) exposure (up to 600 μg/L) in juvenile Tambaqui ( Colossoma macropomum ) exposed in freshly collected Rio Negro (‘black w...

Optical characterization of dissolved organic carbon (DOC) freshly collected from the circumneutral “white water” of the Rio Solimoes revealed that it had lower aromaticity, lower molecular weight, and a greater autochthonous content than DOC from the acidic “black water” of the Rio Negro. The tambaqui ( Colossoma macropomum ), a characid member of the Serrasalmidae, is a model neotropical fish that migrates annually between t...

In the Amazon basin, the white- and blackwater rivers have marked variability in their natural physicochemical characteristics, which impose differential physiological constraints that shape aquatic biodiversity. Thriportheus albus is a Characiform fish widely distributed throughout the different types of water in Amazon basin, with two distinct and isolated populations, a whitewater and a blackwater/clearwater population. In...

The harvest of animals from the wild is a pervasive selective force, especially in fisheries, where harvesting often targets individuals with specific traits. While most research has focused on large‐scale commercial or recreational fisheries, little attention has been paid to artisanal fisheries, particularly those targeting ornamental species. Furthermore, environmental factors such as temperature and oxygen levels influence...