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The composition of the diet of two species of characids (Knodus heteresthes and Moenkhausia lepidura) was evaluated in the Teles Pires and Juruena Rivers, sampled in September and October 2016. We analyzed 226 stomachs of K. heteresthes and 425 of M. lepidura. The analysis of the stomach contents was based on volumetric and frequency of occurrence methods, applying the food importance index. For the similarity of the diets between the species we calculated the niche overlap with Pianka’s index. Both species in the Juruena River have a dietary preference for arthropods (IAi > 0.95). In the Teles Pires River the diet is concentrated in three sources for both species: arthropods (IAi > 0.52), vegetables (IAi > 0.33) and fish (IAi > 0.12). The diet was dissimilar when compared to environments (ANOSIM, R ≥ 0.57, p < 0.001) with high trophic niche overlap (α > 0.97), regardless of the sampled environment. In the Teles Pires River, both species were classified as omnivorous with an insectivorous tendency and in the Juruena River the insectivorous behaviour occurs.

Mercury is a global contaminant naturally found in the Amazon; it can be biomagnified in the aquatic trophic chain. The use of piscivorous avians for mercurial contamination biomonitoring is increasing, mainly due to the non-mobility of mercury in avian feathers. We examined the concentrations of total mercury and methylmercury in different Chloroceryle americana tissues from the Teles Pires and Juruena Rivers in the southern Brazilian Amazon. We also evaluated total mercury in small Characidae fish (potential C. americana food) in the same areas. The results evidenced high mercury concentrations, on average two-times higher in the green kingfishers from the Teles Pires River compared to the Juruena River; the same results were found for the fish specimens. Mercury concentrations were lowest in the muscle, followed by liver and highest in feathers. Fifty-eight per cent of the feather samples from the Juruena River and 90% from the Teles Pires River had total mercury concentrations above 5 µg/g, a level previously associated with adverse effects related to avian breeding. The methylmercury concentration was lowest in the liver, followed by feathers and highest in muscle. Although Juruena River avian feathers had a lower total mercury concentration, > 96% of the total mercury was methylmercury, the highest amount for specimens from both rivers.

Mercury is a global contaminant naturally found in the Amazon; it can be biomagni ed in the aquatic trophic chain. The use of piscivorous avians for mercurial contamination biomonitoring is increasing, mainly due to the non-mobility of mercury in avian feathers. We examined the concentrations of total mercury and methylmercury in different Chloroceryle americana tissues from the Teles Pires and Juruena Rivers in the southern Brazilian Amazon. We also evaluated total mercury in small Characidae sh (potential C. americana food) in the same areas. The results evidenced high mercury concentrations, on average two-times higher in the green king shers from the Teles Pires River compared to the Juruena River; the same results were found for the sh specimens. Mercury concentrations were lowest in the muscle, followed by liver and highest in feathers. Fifty-eight per cent of the feather samples from the Juruena River and 90% from the Teles Pires River had total mercury concentrations above 5 µg/g, a level previously associated with adverse effects related to avian breeding. The methylmercury concentration was lowest in the liver, followed by feathers and highest in muscle. Although Juruena River avian feathers had a lower total mercury concentration, > 96% of the total mercury was methylmercury, the highest amount for specimens from both rivers. Highlights 1-Hg concentrations in King shers exceed the limits established by FAO; 2-Bird feathers can be considered a good indicator of mercury contamination; 3-The percentage of MeHg present in the feathers and liver shows the e ciency of the Hg excretion routes in C. americana.