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Copper oxide nanoparticles (nCuO) are widely used in boat antifouling paints and are released into the environment, potentially inducing toxicity to aquatic organisms. The present study aimed to understand the effects of nCuO and dissolved copper (Cu) on two ornamental Amazon fish species: dwarf cichlid (Apistogramma agassizii) and cardinal tetra (Paracheirodon axelrodi). Fish were exposed to 50% of the LC 50 for nCuO (dwarf cichlid 58.31μgL -1 and cardinal tetra 69.6μgL -1 ) and Cu (dwarf cichlid 20μgL -1 and cardinal tetra 22.9μgL -1 ) for 24, 48, 72 and 96h. Following exposure, aerobic metabolic rate (ṀO 2 ), gill osmoregulatory physiology and mitochondrial function, oxidative stress markers, and morphological damage were evaluated. Our results revealed species specificity in metabolic stress responses. An increase of ṀO 2 was noted in cardinal tetra exposed to Cu, but not nCuO, whereas ṀO 2 in dwarf cichlid showed little change with either treatment. In contrast, mitochondria from dwarf cichlid exhibited increased proton leak and a resulting decrease in respiratory control ratios in response to nCuO and Cu exposure. This uncoupling was directly related to an increase in reactive oxygen species (ROS) levels. Our findings reveal different metabolic responses between these two species in response to nCuO and Cu, which are probably caused by the differences between species natural histories, indicating that different mechanisms of toxic action of the contaminants are associated to differential osmoregulatory strategies among species., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Increasing anthropogenic activities in the Amazon have led to elevated metals in the aquatic environment. Since fish are the main source of animal protein for the Amazonian population, understanding metal bioaccumulation patterns and physiological impacts is of critical importance. Juvenile tambaqui, a local model species, were exposed to chronic dietary Cu (essential, 500 μg Cu/g food) and Cd (non-essential, 500 μg Cd/g food). Fish were sampled at 10-14, 18-20 and 33-36 days of exposure and the following parameters were analyzed: growth, voluntary food consumption, conversion efficiency, tissue-specific metal bioaccumulation, ammonia and urea-N excretion, O 2 consumption, P crit , hypoxia tolerance, nitrogen quotient, major blood plasma ions and metabolites, gill and gut enzyme activities, and in vitro gut fluid transport. The results indicate no ionoregulatory impacts of either of the metal-contaminated diets at gill, gut, or plasma levels, and no differences in plasma cortisol or lactate. The Cd diet appeared to have suppressed feeding, though overall tank growth was not affected. Bioaccumulation of both metals was observed. Distinct tissue-specific and time-specific patterns were seen. Metal burdens in the edible white muscle remained low. Overall, physiological impacts of the Cu diet were minimal. However dietary Cd increased hypoxia tolerance, as evidenced by decreased P crit , increased time to loss of equilibrium, a lack of plasma glucose elevation, decreased plasma ethanol, and decreased NQ during hypoxia. Blood O 2 transport characteristics (P 50 , Bohr coefficient, hemoglobin, hematocrit) were unaffected, suggesting that tissue level changes in metabolism accounted for the greater hypoxia tolerance in tambaqui fed with a Cd-contaminated diet., (Copyright © 2018 Elsevier B.V. All rights reserved.)

We studied the recovery of juvenile fat snook (Centropomus parallelus) after subchronic exposure to different concentrations of copper. Healthy juveniles (1.98 g) were exposed to 25 or 50 μg Cu/L for 30 days (12 replicates with 5 fish in each one), and recovery was observed at 0, 4, 10, and 30 days after exposure (3 replicates with 5 fish in each one). Copper genotoxicity in exposed individuals was observed using a micronucleus assay, and recovery was not observed even 30 days post-exposure. Copper accumulation was observed in fish exposed to 25 or 50 μg/L of copper in the gills (14.4 and 34.4 μg/g, respectively) and muscle (5.7 and 5.5 μg/g, respectively), and a return to normal copper levels (6.0 μg/g for gills and 2.5 μg/g for muscle) was observed 4 and 30 days post-exposure in the gills and muscle tissues, respectively. Glutathione S-transferase (GST) was 80% inhibited in individuals exposed to copper and returned to normal levels for fish exposed to basal concentrations within 10 days. Although copper accumulation in tissues dispersed 30 days post-exposure, no recovery from genotoxicity was observed during this time. Thirty days was not enough to recover juvenile fat snook following subchronic exposure to copper., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The copper sensitivity of 10 wild ornamental fish from Rio Negro, an ion-poor river in the Amazon, was analyzed in the absence of dissolved organic carbon (DOC). No mortality was observed at concentrations up to 700mug Cul(-1) for two species exposed to CuCl(2).2H(2)O dissolved in standard EPA-USA water. Copper sensitivity of fish was also tested in INPA groundwater, which is similar to that of the Rio Negro, but lacking typical DOC of Rio Negro water. In these experiments, all four characid fish species were more sensitive to copper than the catfish and the cichlids. LC(50) values ranged from 12.8mug Cul(-1) for the characid Hemigrammus rhodostomus to 74.1mug Cul(-1) for the callichtyid Dianema urostriatum. Copper sensitivity of Hyphessobrycon socolofi was 52-fold lower in EPA (1405.5mug Cul(-1)) than in INPA water (26.8mugCul(-1)). The differences in values of LC(50) may be related to species-specific physiological abilities to ion-regulate under the original conditions of the habitat of the analyzed species.