The escalating industrial and artisanal extraction of natural resources in the Amazon Basin has centered it into the spotlight of global environmental concern. This study deals with the environmental problems of heavy metals pollution and biomagnification, which stem from mining, agricultural, petrochemical, and industrial discharges. We conducted an extensive investigation, analyzing 360 fish specimens representing 58 species, to assess the concentrations of 11 metals (Al, As, Cd, Cr, Cu, He, Mn, Ni, Pb, Zn, and Hg) along the Ecuadorian sections of the Napo and Pastaza watersheds. Stable isotope analyses (δ¹⁵N and δ¹³C) were employed to determine their trophic positions and potential biomagnification risks. Sampling was carried out during two distinct hydrological seasons to capture seasonal variations in metal concentrations. Furthermore, we estimated species-specific daily heavy metal intake levels. The results of our study revealed that 15 fish species and 53 individual specimens exhibited heavy metal concentrations surpassing recommended standards, with elevated levels of Al, As, and Hg posing significant risks to human consumers with daily intakes of 0.46 kg/day. Notably, our investigation unveiled concerning trends, including increased metal concentrations, Hg biomagnification within fish populations from the Pastaza watershed, and an association between smaller fish size and higher metal content. This study provides a crucial baseline for monitoring future environmental changes and understanding the persistent impacts of heavy metal pollution in the Ecuadorian Amazon region and the broader Western Amazon. It underscores the urgent need for sustainable environmental management practices to mitigate the escalating threat to these vital ecosystems.

Twenty nine species have been added to the annotated checklists of the ichthyofauna of the Caura River Basin, Guiana Shield, Venezuela. Of these, 18 were found in two floodplain lagoons in the lower Caura, corresponding to the orders Characiformes, Clupeiformes, Gymnotiformes, Siluriformes and Perciformes and one species of Tetraodontiformes in the port of Maripa. The others 11 species were found in the upper Caura, representing the orders Characiformes, Gymnotiformes and Siluriformes. Previous ichthyofaunal surveys in the Caura river Basin recorded a total of 514 species, including 150 species for the upper Caura and 492 for the lower Caura. After our recent survey the total number of fish species in the whole drainage basin increased to 543 species, of which 172 and 510 belong to the upper and lower Caura, respectively.

The Arauca River harbors a considerable fish biodiversity, yet it remains poorly sampled and the knowledge about its fish communities is incomplete. We studied the taxonomic and functional composition and diversity of catfish assemblages in one lotic and one lentic habitat of a segment of this floodplain during one hydrological cycle, from August 2014 to August 2015, comprising six samplings using gillnets, and identified the relationships between catfish traits and the environment based on five limnological variables. The functional structure was studied through 11 morphological measures and the species diets. We identified 31 catfish species and nine trophic groups. There were significant differences in species composition and diversity between habitats and months, but the functional structure of the catfishes was only determined by the temporal variability. The functional structure of the catfish assemblages was ordered by morphological traits related to locomotion, habitat use, and trophic ecology and these traits were correlated with the limnological variables, supporting the existence of environmental filters. Integrating the taxonomic and functional perspectives can provide a more complete picture of the ecological patterns of freshwater fish assemblages in the Neotropics and can help us predict how these assemblages might change in response to anthropogenic alterations of the environment.

The co-occurrence patterns of fish communities in the littorals of three lagoons of the Orinoco River floodplain in Venezuela were studied during four hydrological phases: low, rising, high and falling waters, from 2008–2009, using null models. The analyses were made separately for each floodplain lake and for each habitat type within them. During low waters only one lake showed a segregated pattern in beaches covered with leaf litter, whereas in the other floodplain lakes the communities were randomly assembled in all habitats during the four hydrological phases. Despite the absence of a significant overall structure, several significantly aggregated and segregated species pairs were observed in the three lakes. The temporal variation might be the main factor responsible for the co-occurrence patterns observed in these floodplain lakes due to the periodic reshuffling of littoral habitats.

Trace metal pollution in tropical freshwater ecosystems poses growing public health concerns, particularly in regions where fisheries are central to food security; however, little is known about metal exposure risks in the Western Amazon. This study presents the first assessment of trace metal concentrations in fish sold at the main market in El Coca, a rapidly growing city in the Ecuadorian Amazon. We analyzed 11 trace metals in 17 commercially important species and estimated seven health risk indices based on two fish consumption scenarios and international reference dose standards. Our results show that all species exceeded recommended thresholds for arsenic, mercury, and lead, while one species surpassed guidelines for aluminum. Metal concentrations varied by species and river of origin: small catfish from the Payamino River had elevated cadmium, chromium, copper, and manganese levels, potentially linked to upstream gold mining, whereas larger catfish showed higher mercury and arsenic accumulation. Monte Carlo simulations of risk indices suggested overall some disease risk, but the lack of local demographic data limits accurate assessments for vulnerable groups. Despite sampling limitations, our findings offer the first baseline for monitoring trace metal exposure in the northern Ecuadorian Amazon and underscore the need for targeted public health strategies in this understudied region.