Oil spill in an amazon blackwater environment: Biochemical and physiological responses of local fish species.

The accidental spill of petroleum asphalt cement (PAC) in São Raimundo (SR Harbor, located on the Rio Negro (Manaus, Amazonas, Brazil) was monitored through the analysis of polyciclic aromatic hydrocarbons (PAHs) in water and a set of biomarkers in fishes (exposure biomarkes: PAHs-type metabolites concentrations in bile; the activities of ethoxyresorufin-O-deethylase (EROD), glutathione-S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) in liver. Effect biomarkers: lipid peroxidation concentration (LPO) in liver, acetylcholinesterase activity in brain, and genotoxic DNA damage in erythrocytes). Two fish species, Acarichthys heckelii and Satanoperca jurupari, were collected 10, 45, and 90 days after the PAC spill in São Raimundo. At the same time, fish were collected from the Tupé Sustainable Development Reserve (Tupé) which served as a reference area. The sampling periods were related to the rising waters of the natural flood pulse of the Rio Negro. Higher concentrations of PAHs in water were observed at 10 and 45 days and returned to the values of TP 90 days after the PAC spill, a period in which harbor waters rose about 0.2 m. Unlike the PAHs in water, biomarker responses in both fish species significantly increased following the PAC spill in SR. Hepatic ethoxyresorufin-O-deethylase (EROD), PAH-like metabolites in bile, and erythrocyte DNA damage increases, together with inhibition of acetylcholinesterase (AChE) activity in the brain were the most evident responses for both fish species. The calculated pyrolytic index showed mixed sources of PAHs (petrogenic and pyrolytic). The applied PCA-FA indicated important relationships between dissolved organic carbon (DOC) and PAHs concentrations in water, where DOC and PAHs concentrations contributed to biomarkers responses for both fish species in all collection periods.

Investigating the mechanisms of dissolved organic matter protection against copper toxicity in fish of Amazon's black waters.

We investigated how natural dissolved organic matter (DOM) of the Rio Negro (Amazon) affects acute copper (Cu) toxicity to local fish: the cardinal tetra (Paracheirodon axelrodi) and the dwarf cichlid (Apistogramma agassizii). It is established that Cu2+ complexation with DOM decreases Cu bioavailability (and thus toxicity) to aquatic organisms, as conceptualized by the Biotic Ligand Model (BLM). However, we also know that Rio Negro's DOM can interact with fish gills and have a beneficial effect on Na+ homeostasis, the main target of acute Cu toxicity in freshwater animals. We aimed to tease apart these potential protective effects of DOM against Cu-induced Na+ imbalances in fish. In the laboratory, we acclimated fish to Rio Negro water (10 mg L-1 DOC) and to a low-DOM water (1.4 mg L-1 DOC) with similar ion composition and pH (5.9). We measured 3-h Cu uptake in gills and unidirectional and net Na+ physiological fluxes across a range of Cu concentrations in both waters. Various DOM pre-acclimation times (0, 1 and 5 days) were evaluated in experiments with P. axelrodi. Copper exposure led to similar levels of net Na+ loss in the two fish, but with distinct effects on Na+ influx and efflux rates reflecting their different ionoregulation strategies. Rio Negro DOM protected against Cu uptake and toxicity in the two fish species. Both Cu uptake in fish gills and Na+ regulation disturbances were relatively well predicted by the modelled aqueous free Cu2+ ion concentration. These findings suggest that protection by DOM occurs mainly from Cu complexation under the tested conditions. The prevalence of this geochemical-type protection over a physiological-type protection agrees with the BLM conceptual framework, supporting the use of the BLM to assess the risk of Cu in these Amazonian waters.

Ecological adaptations of Amazonian fishes acquired during evolution under environmental variations in dissolved oxygen: A review of responses to hypoxia in fishes, featuring the hypoxia-tolerant Astronotus spp.

The Amazon Basin presents a dynamic regime of dissolved oxygen (DO) oscillations, which varies among habitats within the basin, including spatially, daily, and seasonally. Fish species inhabiting these environments have developed many physiological adaptations to deal with the frequent and periodic events of low (hypoxia), or no (anoxia) DO in the water. Cichlid fishes, especially the genus Astronotus (A. ocellatus and A. crassipinnis), are hypoxic-tolerant species that can survive in very low DO levels for long periods, while adults often inhabit places where DO is close to zero. The present review will focus on some metabolic adjustments that Amazonian fish use in response to hypoxic conditions, which include many strategies from behavioral, morphological, physiological, and biochemical strategies. These strategies include ASR (aerial surface respiration), lip expansion, branchial tissue remodeling, increases in glycolytic metabolism with the increase of blood glucose levels, and increases in anaerobic metabolism with increases of plasma lactate levels. Other groups over evolutionary time developed obligate aerial respiration with changes in pharyngeal and swim bladder vascularization as well as the development of a true lung. However, most species are water-breathing species, such as A. ocellatus and A. crassipinnis, which are detailed in this study because they are used as hypoxia-tolerant model fish. Herein, we draw together the literature data of the physiological mechanisms by which these species decrease aerobic metabolism and increase anaerobic metabolism to survive hypoxia. This is the first attempt to synthesize the physiological mechanisms of the hypoxia-tolerant Astronotus species.

Boron Oxide Nanoparticles Exhibit Minor, Species-Specific Acute Toxicity to North-Temperate and Amazonian Freshwater Fishes.

Boron oxide nanoparticles (nB2O3) are manufactured for structural, propellant, and clinical applications and also form spontaneously through the degradation of bulk boron compounds. Bulk boron is not toxic to vertebrates but the distinctive properties of its nanostructured equivalent may alter its biocompatibility. Few studies have addressed this possibility, thus our goal was to gain an initial understanding of the potential acute toxicity of nB2O3 to freshwater fish and we used a variety of model systems to achieve this. Bioactivity was investigated in rainbow trout (Oncorhynchus mykiss) hepatocytes and at the whole animal level in three other North and South American fish species using indicators of aerobic metabolism, behavior, oxidative stress, neurotoxicity, and ionoregulation. nB2O3 reduced O. mykiss hepatocyte oxygen consumption (MO2) by 35% at high doses but whole animal MO2 was not affected in any species. Spontaneous activity was assessed using MO2 frequency distribution plots from live fish. nB2O3 increased the frequency of high MO2 events in the Amazonian fish Paracheirodon axelrodi, suggesting exposure enhanced spontaneous aerobic activity. MO2 frequency distributions were not affected in the other species examined. Liver lactate accumulation and significant changes in cardiac acetylcholinesterase and gill Na+/K+-ATPase activity were noted in the north-temperate Fundulus diaphanus exposed to nB2O3, but not in the Amazonian Apistogramma agassizii or P. axelrodi. nB2O3 did not induce oxidative stress in any of the species studied. Overall, nB2O3 exhibited modest, species-specific bioactivity but only at doses exceeding predicted environmental relevance. Chronic, low dose exposure studies are required for confirmation, but our data suggest that, like bulk boron, nB2O3 is relatively non-toxic to aquatic vertebrates and thus represents a promising formulation for further development.

Gills versus kidney for ionoregulation in the obligate air-breathing Arapaima gigas, a fish with a kidney in its air-breathing organ.

In Arapaima gigas, an obligate air-breather endemic to ion-poor Amazonian waters, a large complex kidney runs through the air-breathing organ (ABO). Previous indirect evidence suggested that the kidney, relative to the small gills, may be exceptionally important in ionoregulation and nitrogen (N) waste excretion, with support of kidney function by direct O2 supply from the airspace. We tested these ideas by continuous urine collection and gill flux measurements in ∼700 g fish. ATPase activities were many-fold greater in kidney than gills. In normoxia, gill Na+ influx and efflux were in balance, with net losses of Cl- and K+ Urine flow rate (UFR, ∼11 ml kg-1 h-1) and urinary ions (< 0.2 mmol l-1) were exceptional, with [urine]:[plasma] ratios of 0.02-0.002 for K+, Na+, and Cl-, indicating strong reabsorption with negligible urinary ion losses. Urinary [ammonia] was very high (10 mmol l-1, [urine]:[plasma] ∼17) indicating strong secretion. The kidney accounted for 21-24% of N excretion, with ammonia dominating (95%) over urea-N through both routes. High urinary [ammonia] was coupled to high urinary [HCO3-]. Aerial hypoxia (15.3 kPa) and aerial hyperoxia (>40.9 kPa) had no effects on UFR, but both inhibited branchial Na+ influx, revealing novel aspects of the osmorespiratory compromise. Aquatic hypoxia (4.1 kPa), but not aquatic hyperoxia (>40.9 kPa), inhibited gill Na+ influx, UFR and branchial and urinary ammonia excretion. We conclude that the kidney is more important than gills in ionoregulation, and is significant in N excretion. Although not definitive, our results do not indicate direct O2 supply from the ABO for kidney function.

High Temperature, pH, and Hypoxia Cause Oxidative Stress and Impair the Spermatic Performance of the Amazon Fish Colossoma macropomum.

The control of abiotic parameters is fundamental for fish survival, growth and reproduction. These factors have a direct effect on sperm quality. Thus, this study evaluated the effect of different temperatures (29, 31, 33, and 35°C), pHs (4 and 8), and hypoxia (1 mgO2 L-1) on sperm motility of Colossoma macropomum (tambaqui). The results indicated a longer duration of sperm motility at 29°C (50.1 ± 2.70 s) that progressively decreased when exposed to 35°C (31.2 ± 1.31 s) and hypoxia at pH 4 (27.4 ± 1.42 s) and pH 8 (30.44 ± 1.66 s; p < 0.05), respectively. Sperm oxygen consumption increased in hypoxia at both pH (pH 4 = 61.22; pH 8 = 54.74 pmol s-1). There was an increase in the activity of glutathione-S-transferase (GST) and superoxide dismutase (SOD), as well as in lipid peroxidation levels (LPO) and DNA damage in sperm exposed to higher temperatures and hypoxia. The pH 4 and pH 8 under normoxia did not affect the quality of C. macropomum sperm. These results suggest that water warming and acidification, consequences of climate changes, significantly affect the reproduction of C. macropomum, reducing the quality of spermatozoids during fertilization.

Gills and air-breathing organ in O2 uptake, CO2 excretion, N-waste excretion, and ionoregulation in small and large pirarucu (Arapaima gigas).

In the pirarucu (Arapaima gigas), gill surface area and thus gas exchange capacity of the gills are reduced with proceeding development. It, therefore, is expected that A. gigas, starting as a water breather, progressively turns into an obligate air-breathing fish using an air-breathing organ (ABO) for gas exchange. We assessed the air-breathing activity, O2 and CO2 exchange into air and water, ammonia-N and urea-N excretion, ion flux rates, and activities of ion transport ATPases in large versus small pirarucu. We found that even very young A. gigas (4-6 g, 2-3 weeks post-hatch) with extensive gills are air-breathers (18.1 breaths*h-1) and cover most (63%) of their O2 requirements from the air whereas 600-700-g animals (about 3-4 months post-hatch), with reduced gills, obtain 75% of their O2 from the air (10.8 breaths*h-1). Accordingly, the reduction in gill surface area hardly affected O2 uptake, but development had a significant effect on aerial CO2 excretion, which was very low (3%) in small fish and increased to 12% in larger fish, yielding a hyper-allometric scaling coefficient (1.12) in contrast to 0.82-0.84 for aquatic and total CO2 excretion. Mass-specific ammonia excretion decreased in approximate proportion to mass-specific O2 consumption as the fish grew, but urea-N excretion dropped from 18% (at 4-6 g) to 8% (at 600-700 g) of total N-excretion; scaling coefficients for all these parameters were 0.70-0.80. Mass-specific sodium influx and efflux rates, as well as potassium net loss rates, departed from this pattern, being greater in larger fish; hyper-allometric scaling coefficients were > 1.0. Gill V-type H+ ATPase activities were greater than Na+, K+-ATPase activities, but levels were generally low and comparable in large and small fish, and similar activities were detected in the ABO. A. gigas is a carnivorous fish throughout its lifecycle, and, despite fasting, protein oxidation accounted for the major portion (61-82%) of aerobic metabolism in both large and small animals. ABO PO2 and PCO2 (measured in 600-700-g fish) were quite variable, and aerial hypoxia resulted in lower ABO PO2 values. Under normoxic conditions, a positive correlation between breath volume and ABP PO2 was detected, and on average with a single breath more than 50% of the ABO volume was exchanged. ABO PCO2 values were in the range of 1.95-3.89 kPa, close to previously recorded blood PCO2 levels. Aerial hypoxia (PO2 down to 12.65 kPa) did not increase either air-breathing frequency or breath volume.

Does hypoxia or different rates of re-oxygenation after hypoxia induce an oxidative stress response in Cyphocharax abramoides (Kner 1858), a Characid fish of the Rio Negro?

We examined whether oxidative damage and antioxidant responses are more likely to occur during hypoxia or re-oxygenation in hypoxia-tolerant fish, and whether there is an influence of the rate of re-oxygenation. An hypoxia/re-oxygenation experiment using wild-caught Cyphocharax abramoides (Rio Negro, Brazil), was designed to answer these questions. Lipid peroxidation (MDA), a measure of oxidative damage, and antioxidant activities (superoxide dismutase (SOD), glutathione peroxidase (GPx), antioxidant capacity against peroxyl radicals (ACAP)), were measured in brain, gill and liver tissues after normoxia, 3-h hypoxia (2.7 kPa), and 3-h hypoxia followed by 1-h or 3-h re-oxygenation, implemented either immediately or slowly (3.0 kPa·h-1). Critical oxygen tension of routine oxygen consumption rate (Pcrit) (4.1 kPa) and the PO2 at loss of equilibrium (LOE) (1.7 kPa) were determined to set the experimental hypoxia exposure. The Regulation Index, a measure of oxyregulation with declining PO2, was 0.32. Oxidative damage occurred during hypoxia: no additional damage was observed during re-oxygenation. Tissues responded differentially. GPx and MDA rose in the brain and gills, and SOD (and likely GPx) in the liver during hypoxia. Antioxidants increased further at LOE. Rate of oxygen increase during re-oxygenation did not affect antioxidant responses. In brain and gills, GPx and MDA decreased or recovered after 1-h re-oxygenation. In liver, SOD remained high and GPx increased. In summary, C. abramoides incurred oxidative damage during hypoxic exposure with no additional damage inflicted during re-oxygenation: the rate of re-oxygenation was inconsequential. Literature data support conclusion of greater damage during hypoxia than during re-oxygenation in hypoxia-tolerant fish.

Mechanisms of toxic action of copper and copper nanoparticles in two Amazon fish species: Dwarf cichlid (Apistogramma agassizii) and cardinal tetra (Paracheirodon axelrodi).

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 LC50 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 (MO2), 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 MO2 was noted in cardinal tetra exposed to Cu, but not nCuO, whereas MO2 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.

The physiology of the Tambaqui (Colossoma macropomum) at pH 8.0.

The Tambaqui is a model neotropical teleost which is of great economic and cultural importance in artisanal fisheries and commercial aquaculture. It thrives in ion-poor, often acidic Amazonian waters and exhibits excellent regulation of physiology down to water pH 4.0. Curiously, however, it is reported to perform poorly in aquaculture at pH 8.0, an only slightly alkaline pH which would be benign for most freshwater fish. In initial experiments with Tambaqui of intermediate size (30-50 g), we found that ammonia excretion rate was unchanged at pH 4, 5, 6, and 7, but elevated after 20-24 h at pH 8, exactly opposite the pattern seen in most teleosts. Subsequent experiments with large Tambaqui (150-300 g) demonstrated that only ammonia, and not urea excretion was increased at pH 8.0, and that the elevation was proportional to a general increase in MO2. There was an accompanying elevation in net acidic equivalent excretion and/or basic equivalent uptake which occurred mainly at the gills. Net Na+ balance was little affected while Cl- balance became negative, implicating a disturbance of Cl- versus base exchange rather than Na+ versus acid exchange. Arterial blood pH increased by 0.2 units at pH 8.0, reflecting combined metabolic and respiratory alkaloses. Most parameters recovered to control levels by 18-24 h after return to pH 6.0. With respect to large Tambaqui, we conclude that a physiology adapted to acidic pH performs inappropriately at moderately alkaline pH. In small Tambaqui (4-15 g), the responses were very different, with an initial inhibition of ammonia excretion rate at pH 8.0 followed by a subsequent restoration of control levels. Elevated ammonia excretion rate occurred only after return to pH 6.0. Furthermore, MO2, plasma cortisol, and branchial vH+ATPase activities all declined during pH 8.0 exposure in small Tambaqui, in contrast to the responses in larger fish. Overall, small Tambaqui appear to cope better at pH 8.0, a difference that may correlate with their natural history in the wild.

Influence of the natural Rio Negro water on the toxicological effects of a crude oil and its chemical dispersion to the Amazonian fish Colossoma macropomum.

The increment in crude oil exploitation over the last decades has considerably increased the risk of polycyclic aromatic hydrocarbon (PAH) contamination to Amazonian aquatic environments, especially for the black water environments such as the Rio Negro. The present work was designed to evaluate the acute toxicity of the Urucu crude oil (CO), the chemically dispersed Urucu crude oil (CO + D), and the dispersant alone (D) to the Amazonian fish Colossoma macropomum. Acute toxicity tests were performed, using a more realistic approach, where fish were acclimated to both groundwater (GW), used as internal control, and natural Rio Negro water (RNW) and exposed to CO, CO + D and D. Then, biomarkers such as ethoxyresorufin-O-deethylase (EROD), superoxide dismutase (SOD), lipid peroxidation (LPO), serum sorbitol dehydrogenase (s-SDH) in liver, DNA damage in blood cells, and the presence of the benzo[a]pyrene-type, pyrene-type, and naphthalene-type metabolites in fish bile were assessed. Fish exposed to CO and CO + D, at both water types tested, presented increased biomarker responses and higher PAH-type metabolites in the bile. However, fish exposed to these treatments after the acclimation to RNW increased the levels of LPO, s-SDH (hepatotoxicity), DNA damage in blood cells (genotoxicity), and benzo[a]pyrene-type metabolites when compared to fish in GW. Our data suggests that some physicochemical properties of Rio Negro water (i.e., presence of natural organic matter (NOM)) might cause mild chemical stress responses in fish, which can make it more susceptible to oxidative stress following exposure to crude oil, particularly to those chemically dispersed.

Roundup® exposure promotes gills and liver impairments, DNA damage and inhibition of brain cholinergic activity in the Amazon teleost fish Colossoma macropomum.

Roundup Original® (RD) is a glyphosate-based herbicide used to control weeds in agriculture. Contamination of Amazon waters has increased as a consequence of anthropogenic pressure, including the use of herbicides as RD. The central goal of this study was to evaluate the toxic effects of RD on juveniles of tambaqui (Colossoma macropomum). Our findings show that biomarkers in tambaqui are organ specific and dependent on RD concentration. Alterations in gills structural and respiratory epithelium were followed by changes in hematological parameters such as concentration of hemoglobin, particularly in fish exposed to the higher concentration tested (75% of RD LC50 96 h). In addition, both RD concentrations affected the biotransformation process in gills of tambaqui negatively. Instead, liver responses suggest that a production of reactive oxygen species (ROS) occurred in fish exposed to RD, particularly in the animals exposed to 75% RD, as seen by imbalances in biotransformation and antioxidant systems. The increased DNA damage observed in red blood cells of tambaqui exposed to RD is in agreement with this hypothesis. Finally, both tested sub-lethal concentrations of RD markedly inhibited the cholinesterase activity in fish brain. Thus, we can suggest that RD is potentially toxic to tambaqui and possibly to other tropical fish species.