What happens to Hoplias malabaricus fed on live prey (Astyanax altiparanae) previously exposed to copper? A multiple biomarker approach.

Copper waterborne toxicity is well understood in aquatic organisms. However, the dietary copper effects are much less known, especially in tropical fish. The toxicity of copper via the trophic route could be influenced by the composition of the food, and diets naturally impregnated with copper seem to have greater toxicity at lower concentrations than artificially impregnated ones. Thus, our objective was to investigate the effects of copper on juveniles of the Neotropical fish Hoplias malabaricus fed on live prey (Astyanax altiparanae) previously exposed to the metal (20 µg L - 1) for 96 h. The prey fish were given to H. malabaricus every 96 h, totaling 10 doses at the end of the experiment. Thus, after 40 days fish were killed and tissues were sampled. Blood showed to be the only tissue in which copper accumulated. Anemia was found and there was damage to the DNA of erythrocytes. Furthermore, ionic imbalances were observed in plasma. There was an increase in the concentration of Na+ and Cl- and a decrease in Ca2+, which were associated with increased copper uptake in the gastrointestinal tract of fish fed on copper exposed prey. All the antioxidant enzymes evaluated in the gills showed decreased activity compared to the control group. Copper seems to have interfered in the energy metabolism of H. malabaricus, since a lower condition factor and feed conversion efficiency rate were observed in fish fed with copper diet. The present study confirms the trophic route as an important copper toxicity pathway for H. malabaricus and reinforces the idea that metal toxicity can be increased when it is naturally impregnated in the prey tissues, even if the prey has been exposed to the metal only for a short period of time.

Effects of copper on an omnivorous (Astyanax altiparanae) and a carnivorous fish (Hoplias malabaricus): A comparative approach.

Copper is an essential metal for life. However, in excess, it can lead to osmoregulatory disorders and oxidative stress in fish and these effects appear to be species specific. In order to evaluate the effects of copper and to compare the sensitivity of two Neotropical fishes that co-occur in nature as prey (Astyaynax altiparanae) and predator (Hoplias malabaricus), the fish were exposed to three concentrations of Cu (5 µg L-1, 10 µg L-1, and 20 µg L-1) for 96 h. At the end of the experimental period, copper concentration in tissues, osmoregulatory parameters, oxidative stress biomarkers, plasma glucose, muscle glycogen and acetylcholinesterase activity were evaluated. Fish mortality (25%) was only observed for A. altiparanae exposed to Cu 20 µg L-1. The results revealed species-specific ionic disturbances. Despite hypocalcemia, H. malabaricus showed an increase in the main gill ATPases, which probably guaranteed the maintenance of plasma Na+.  In A. altiparanae, there was no change in ATPase activity in the gills and hyponatremia was observed at all copper concentrations, as well as a decrease in plasma Cl- in the Cu 20 µg L-1 group. The strategy adopted by H. malabaricus seems to have contributed to the absence of copper accumulation in the tissues, in addition to possibly being related to the absence of oxidative stress in this species. On the other hand, there was an increase in the concentration of copper in the gills, liver, and gastrointestinal tract of A. altiparanae, as well as oxidative stress evidenced by increased lipoperoxidation in the liver and damage to erythrocytes DNA. This work reinforces the idea that copper effects are species specific and that a given concentration may not be safe for different species which can coexist in the same environment.

Sublethal effects of waterborne copper and copper nanoparticles on the freshwater Neotropical teleost Prochilodus lineatus: A comparative approach.

Copper nanoparticles can contaminate the aquatic environment, but their effects on fish and how they may differ from copper salts is not understood. Thus, in this work we compare the sublethal effects of copper nanoparticles (nCu) and copper chloride (Cu) on the freshwater teleost Prochilodus lineatus, known for its sensitivity to copper. Juveniles (n = 8/group) were exposed to 20 µg L-1 of copper as CuCl2 (Cu), 40 µg L-1 of copper nanoparticles (nCu), or only water (control), for 96 h. These concentrations were chosen to achieve similar dissolved copper concentration in both treatments (Cu: 10.29 ± 0.94 µg L-1; nCu: 12.16 ± 1.77 µg L-1). After the exposure, the following biological parameters were evaluated: copper accumulation in the gills, liver, gastrointestinal tract, kidney, and muscle; hematocrit (Ht) and hemoglobin content (Hb); branchial activity of Na+-K+-ATPase (NaKATP), H+-ATPase (HATP), Ca2+-ATPase (CaATP), and carbonic anhydrase (CA); glutathione content (GSH) and lipid peroxidation (LPO) in the liver; acetylcholinesterase activity (AChE) in the brain and muscle; and histopathology of the gills and liver. The gills of Cu-exposed fish were adversely affected, with increased copper content, inhibition of H+-ATPase and Ca2+-ATPase, and histological damage, including proliferation of mitochondria rich cells and/or mucous cells. In addition, LPO levels increased in the liver of Cu-exposed fish, indicating the occurrence of oxidative stress. Exposure to nCu promoted a decrease in Ht and Hb, indicating anemia, and an increase in branchial Na+-K+-ATPase and H+-ATPase activities, which can be an adaptive response to metabolic acidosis. Within the chosen biomarkers and the conditions tested, copper nanoparticles were less toxic than copper. However, the effects promoted by the nanoparticles were different from those promoted by copper. These results emphasize the need for a better understanding of copper nanoparticles toxicity in order to establish safe concentrations and avoid environment impacts.