First account of plastic pollution impacting freshwater fishes in the Amazon: Ingestion of plastic debris by piranhas and other serrasalmids with diverse feeding habits

Reported here is the first evidence of plastic ingestion by freshwater fishes in the Amazon. Plastic bags, bottles, fishing gear, and other products are entering Amazonian water bodies and degrade into meso- and micro-plastic particles that may be ingested, either directly or indirectly via food chains, by fishes. Examination of stomach contents from 172 specimens of 16 serrasalmid species from lower Xingu River Basin revealed consumption of plastic particles by fishes in each of three trophic guilds (herbivores, omnivores, carnivores). Overall, about one quarter of specimens and 80% of species analyzed had ingested plastic particles ranging from 1 to 15 mm in length. Fourier transform infrared spectroscopy indicated 12 polymer types, including 27% identified as polyethylene, 13% polyvinyl chloride, 13% polyamide, 13% polypropylene, 7% poly(methyl methacrylate), 7% rayon, 7% polyethylene terephtalate, and 13% a blend of polyamide and polyethylene terephtalate. Dimensions of ingested plastic particles varied among trophic guilds, even though the frequency and mass of ingested particles were not significantly different among fishes with different feeding habits.

Microplastics and copper effects on the neotropical teleost Prochilodus lineatus: Is there any interaction?

Microplastics (MP) are emerging contaminants widely found in aquatic ecosystems. In addition to MP toxicity itself, there is increasing concern about the MP adsorption capacity and the interactive effects with other contaminants, such as copper. The objective of this research was to investigate the effects of polyethylene microplastic and its association with copper (Cu) in genotoxic, biochemical, and physiological biomarkers of the neotropical teleost Prochilodus lineatus. Fish were exposed for 24 and 96 h to MP (20 μg L^-1) and Cu (10 μg L^-1) and MP + Cu. The results showed that MP and Cu, both isolated and in combination, promoted DNA damage in erythrocytes (96 h) and liver cells (24 and 96 h) indicating that MP and Cu are genotoxic. Fish exposed only to Cu (96 h) showed a decrease in lipid peroxidation in the liver despite of the decrease in glutathione content, indicating the efficiency of other antioxidant defenses. Brain acetylcholinesterase was inhibited in the animals from all the treatments. Although MP did not influence on Cu accumulation in tissues, decreased plasma Na⁺ and Ca²⁺ (24 h) occurred after the exposure to MP and Cu, isolated and combined. Exposure to MP and MP + Cu resulted in decreased activity of Ca²⁺-ATPase (24 h). Taken altogether, these results showed that MP and Cu depicted genotoxic, neurotoxic, and physiological effects on P. lineatus, both alone and combined. An interaction between Cu and MP was observed in plasma Ca²⁺, where the combination of both contaminants caused a greater effect than the contaminants alone.

Evolutionary shift towards lateral line dependent prey capture behavior in the blind Mexican cavefish

Feeding strategies are dependent on multi-modal sensory processing, that integrates visual, chemosensory, and mechanoreceptive cues. In many fish species, local environments and food availability dramatically influence the evolution of sensory and morphological traits that underlie feeding. The Mexican cavefish, Astyanax mexicanus, have developed robust changes in sensory-dependent behaviors, but the impact on prey detection and feeding behavior is not known. In the absence of eyes, cavefish have evolved enhanced sensitivity of the lateral line, comprised of mechanosensory organs that sense water flow and detect prey. Here, we identify evolved differences in prey capture behavior of larval cavefish that are dependent on lateral line sensitivity. Under lighted conditions, cavefish strike Artemia prey at a wider angle than surface fish; however, this difference is diminished under dark conditions. In addition, the strike distance is greater in cavefish than surface fish, revealing an ability to capture, and likely detect, prey at greater distances. Experimental ablation of the lateral line disrupts prey capture in cavefish under both light and dark conditions, while it only impacts surface fish under dark conditions. Together, these findings identify an evolutionary shift towards a dependence on the lateral line for prey capture in cavefish, providing a model for investigating how loss of visual cues impacts multi-modal sensory behaviors.

Molecular cloning and expression analysis of dmrt1 and sox9 during gonad development and male reproductive cycle in the lambari fish, Astyanax altiparanae

BACKGROUND

The dmrt1 and sox9 genes have a well conserved function related to testis formation in vertebrates, and the group of fish presents a great diversity of species and reproductive mechanisms. The lambari fish (Astyanax altiparanae) is an important Neotropical species, where studies on molecular level of sex determination and gonad maturation are scarce.

METHODS

Here, we employed molecular cloning techniques to analyze the cDNA sequences of the dmrt1 and sox9 genes, and describe the expression pattern of those genes during development and the male reproductive cycle by qRT-PCR, and related to histology of the gonad.

RESULTS

Phylogenetic analyses of predicted amino acid sequences of dmrt1 and sox9 clustered A. altiparanae in the Ostariophysi group, which is consistent with the morphological phylogeny of this species. Studies of the gonad development revealed that ovary formation occurred at 58 days after hatching (dah), 2 weeks earlier than testis formation. Expression studies of sox9 and dmrt1 in different tissues of adult males and females and during development revealed specific expression in the testis, indicating that both genes also have a male-specific role in the adult. During the period of gonad sex differentiation, dmrt1 seems to have a more significant role than sox9. During the male reproductive cycle dmrt1 and sox9 are down-regulated after spermiation, indicating a role of these genes in spermatogenesis.

CONCLUSIONS

For the first time the dmrt1 and sox9 were cloned in a Characiformes species. We show that both genes have a conserved structure and expression, evidencing their role in sex determination, sex differentiation and the male reproductive cycle in A. altiparanae. These findings contribute to a better understanding of the molecular mechanisms of sex determination and differentiation in fish.

The pyrethroid λ-cyhalothrin induces biochemical, genotoxic, and physiological alterations in the teleost Prochilodus lineatus

The λ-cyhalothrin (CL) is a globally used pyrethroid insecticide that has been detected in different water bodies worldwide. However, studies on the effects of CL on freshwater fishes are still incipient. In this context, we evaluated the acute effects of a commercial formulation containing CL (Karate Zeon^® CS 50) in juveniles of the teleost Prochilodus lineatus exposed for 96 h to four concentrations of the active ingredient (5, 50, 250 and 500 ng.L^-1). Biochemical, physiological, and genotoxic biomarkers were evaluated in different organs of the fish. Exposure to CL induced significant changes in the enzymatic profiles of P. lineatus, with specific alterations in biotransformation enzymes and antioxidant defence in different tissues. Lipid peroxidation was observed in fish gills and kidney. Increases in esterases were observed in the liver of fish exposed to all CL concentrations evaluated, whereas acetylcholinesterase activity decreased in the muscles of fish at all concentrations. CL also promoted osmoregulatory disorders, with decreases in calcium and magnesium gill ATPases, with consequent hypocalcaemia, in addition an increase in sodium-potassium ATPase activity was observed in the gills of fish exposed to the highest CL concentration, probably in order to compensate a reduction in plasma sodium. Besides, increases in DNA damage were observed in the erythrocytes of fish exposed to all CL concentrations. Thus, despite the low CL concentrations and the short exposure time, this pyrethroid caused hematological adjustments, oxidative stress, osmoregulatory disorders, and DNA damage in P. lineatus, showing that the species is highly sensitive to the deleterious effects of CL.

Appetite regulating peptides in red-bellied piranha, Pygocentrus nattereri: cloning, tissue distribution and effect of fasting on mRNA expression levels

cDNAs encoding the appetite regulating peptides apelin, cocaine and amphetamine regulated transcript (CART), cholecystokinin (CCK), peptide YY (PYY) and orexin were isolated in red-bellied piranha and their mRNA tissue and brain distributions examined. When compared to other fish, the sequences obtained for all peptides were most similar to that of other Characiforme fish, as well as to Cypriniformes. All peptides were widely expressed within the brain and in several peripheral tissues, including gastrointestinal tract. In order to assess the role of these peptides in the regulation of feeding of red-bellied piranha, we compared the brain mRNA expression levels of these peptides, as well as the gut mRNA expression of CCK and PYY, between fed and 7-day fasted fish. Within the brain, fasting induced a significant increase in both apelin and orexin mRNA expressions and a decrease in CART mRNA expression, but there where were no significant differences for either PYY or CCK brain mRNA expressions between fed and fasted fish. Within the intestine, PYY mRNA expression was lower in fasted fish compared to fed fish but there was no significant difference for CCK intestine mRNA expression between fed and fasted fish. Our results suggest that these peptides, perhaps with the exception of CCK, play a major role in the regulation of feeding of red-bellied piranha.

Can atrazine loaded nanocapsules reduce the toxic effects of this herbicide on the fish Prochilodus lineatus? A multibiomarker approach

Atrazine (ATZ) is a widely used herbicide that has the potential to contaminate the environment and cause deleterious effects on non-target organisms. Release systems for ATZ have been developed to minimize this contamination, such as nanocapsules prepared with poly (ε-caprolactone) (PCL). The objective of this work was to investigate the effects of nanoencapsulated ATZ compared to ATZ on biomarkers of the freshwater teleost Prochilodus lineatus. The fish were exposed for 24 and 96 h to nanoencapsulated ATZ (nATZ) and atrazine (ATZ) at concentrations of 2 and 20 μg L^-1, just to the PCL nanocapsules without the herbicide (NANO) in the corresponding amounts or only to dechlorinated water (CTR). The results showed that nATZ was less toxic compared to ATZ, as it did not promote an increase in glycemia, alterations in antioxidants, nor in carbonic anhydrase enzyme activity, and no increase in the frequency of micronuclei and other nuclear erythrocyte abnormalities either. However, exposure to nATZ, as well as to ATZ and PCL nanocapsules, resulted in a reduction in hemoglobin content, increase in erythrocyte DNA damage, as well as changes in Ca²⁺-ATPase activity, leading to a decrease in plasma Ca⁺². The Integrated Biomarker Response Index (IBR) depicted that exposure to ATZ promoted changes in a greater number of biomarkers compared to nATZ, indicating that the nanoencapsulation of the herbicide protected the animal from the effects of ATZ.

Cloning, tissue distribution and effects of fasting on mRNA expression levels of leptin and ghrelin in red-bellied piranha (Pygocentrus nattereri)

cDNAs encoding the appetite regulating peptides leptin and ghrelin were isolated in red-bellied piranha (Characiforme, Serrasalmidae) and their mRNA tissue and brain distributions examined. When compared to other fish, the sequences obtained for all peptides were most similar to that of other Characiforme fish and Siluriformes. All peptides were widely expressed within the brain and in several peripheral tissues, including gastrointestinal tract. In order to better understand the role of these peptides in the regulation of feeding of red-bellied piranha, the mRNA expression levels of leptin and ghrelin were examined in both brain and intestine, in fed and 7-day fasted fish. No significant differences in expression were seen in whole brain for either peptide. Within the intestine, there was a decrease in leptin mRNA expression and an increase in ghrelin mRNA expression in fasted fish, compared to fed fish. The results suggest that leptin and ghrelin might play a major role in the regulation of feeding and energy homeostasis of red-bellied piranha and this role might be more prominent in the intestine than in the brain.

Long-term organic selenium supplementation overcomes the trade-off between immune and antioxidant systems in pacu (Piaractus mesopotamicus)

Selenium (Se) is an essential nutrient for antioxidant defenses in fish because of its role in preventing immunosuppression caused by oxidative stress. In this study it was demonstrated the relation between the oxidative stress and immune status after a long Se supplementation period, as a result of the evaluation of immunological, hematological and antioxidant responses, as well as growth performance of pacu fed diets supplemented with different concentrations of organic selenium (0, 0.3, 0.6, 0.9, and 1.8 mg Se-yeast/kg, but the final analyzed selenium concentrations were 0.72, 0.94, 1.15, 1.57 and 2.51 mg/kg, respectively) for 65 days. Dietary Se supplementation at 1.15 mg Se-yeast/kg (analyzed value) restored the production of antioxidant enzymes (glutathione peroxidase (GPx) and glutathione S-transferase (GST)), and consequently allowed the increased of some immunological parameters (leukocyte respiratory burst activity and lysozyme activity), hematological parameters (red blood cell count (RBC), hematocrit (HTC), mean corpuscular volume (MCV), and white blood cell count (WBC)). Se supplementation in pacu diets at 1.15 mg Se-yeast/kg for 65 days improved immune response and antioxidant defenses, suggesting that oxidative stress impairs immune system response to prevent excessive reactive oxygen species in cells and indicating the occurrence of a physiological trade-off between immune and antioxidant systems. Higher Se levels, such as 1.57 mg Se-yeast/kg increased the leukocyte respiratory burst activity, the WBC and thrombocyte counts, the RBC and HTC, and the GST and GPx enzymes. However, 2.51 mg Se-yeast/kg decreased the lysozyme levels, the WBC and thrombocyte counts, the RBC, HTC and MCV, and the GST and GPx enzymes. Those findings are important to future studies because showed the negative effect of oxidative stress on immunity, and may help to prevent any inhibition of the expected immune response after immunomodulators administration and vaccination. Also it was possible to meet the dietary selenium requirement of pacu, that was estimated to be 1.56 mg/kg.

Sweet fish: Fish models for the study of hyperglycemia and diabetes

Fish are good for your health in more ways than you may expect. For one, eating fish is a common dietary recommendation for a healthy diet. However, fish have much more to provide than omega-3 fatty acids to your circulatory system. Some fish species now serve as important and innovative model systems for diabetes research, providing novel and unique advantages compared with classical research models. Not surprisingly, the largest share of diabetes research in fish occurs in the laboratory workhorse among fish, the zebrafish (Danio rerio). Established as a genetic model system to study development, these small cyprinid fish have eventually conquered almost every scientific discipline and, over the past decade, have emerged as an important model system for metabolic diseases, including diabetes mellitus. In this review we highlight the practicability of using zebrafish to study diabetes and hyperglycemia, and summarize some of the recent research and breakthroughs made using this model. Equally exciting is the appearance of another emerging discipline, one that is taking advantage of evolution by studying cases of naturally occurring insulin resistance in fish species. We briefly discuss two such models in this review, namely the rainbow trout (Oncorhynchus mykiss) and the cavefish (Astyanax mexicanus).

Assessment of biomarkers in the neotropical fish Brycon amazonicus exposed to cypermethrin-based insecticide

The effects of cypermethrin-based insecticide (CBI), commonly used in aquaculture and agriculture, were evaluated in matrinxa (Brycon amazonicus) exposed to sub-lethal concentration (20% of LC50) for 96 h. Physiological and biochemical effects were studied through biomarkers: lipid peroxidation (LPO), glutathione (GSH), and ascorbic acid concentrations; superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glucose-6-phosphate dehydrogenase (G6PDH) assays in the liver and gills. Besides, ions Na⁺, Cl^-, and K⁺; protein and glucose concentrations were measured in the plasma. Red blood cells count (RBC), hemoglobin concentration (Hb), hematocrit (Ht), and hematimetric parameters were evaluated in the total blood. The NKA (Na⁺ /K+ ATPase) activity was assayed in the gills. The histopathological effects of CBI were also investigated in the gills. The liver and gill LPO increased 62 and 100%, respectively. The tripeptide GSH concentration reduced in the liver and increased in the gill of exposed fish. The SOD and CAT activities increased in the liver, whereas CAT reduced in the gill. Liver also presented an increase in G6PDH activity. Plasma Na⁺ and Cl^- and glucose concentrations increased in the exposed fish. Levels of Ht, Hb and RBC were significantly increased. The gill NKA activity also increased. Exposed fish exhibited histological alterations in the gills such as hypertrophy and proliferation of chloride cells, blood vessels dilation, aneurysms and hemorrhage of the lamella. The histological index indicated moderate to heavy damage to the gills. CBI provokes liver and gills oxidative stress, gill structural damages, and ionic imbalance. A multi-biomarker approach allows us to see that B. amazonicus was unable to cope with CBI exposure.

Temperature preference of cave and surface populations of Astyanax mexicanus

Little is known about the genetic basis of behavioral choice, such as temperature preference, especially in natural populations. Thermal preference can play a key role in habitat selection, for example in aquatic species. Examining this behavior on a genetic level requires access to individuals or populations of the same species that display distinct temperature preferences. Caves provide a uniquely advantageous setting to tackle this problem, as animals colonizing caves encounter an environment that generally has a different, and far more stable, annual temperature than what is encountered on the outside. Here, we focus on cave and surface populations of Astyanax mexicanus, the Mexican tetra, and examine temperature preference and strength of temperature preference (reflected in the percent of time spent at the optimal temperature). We used a tank with a stable temperature gradient and automated tracking software to follow individual fish from each population. We found that distinct populations of A. mexicanus display differences in both temperature preference and strength of preference. Hybrid crosses established that these are multigenic traits that segregate independently from one another. Temperature preference in many aquatic animals is known to shift towards warmer temperatures following infection with parasites (akin to a fever response in humans). While surface fish infected by the ectoparasite Gyrodactylus turnbulli (a gill fluke) displayed a strong fever response, cavefish showed a significantly attenuated fever response. This work establishes A. mexicanus as a genetically tractable system in which differences in temperature preference can be studied in naturally evolved populations.

Microcystin - LR exposure causes cardiorespiratory impairments and tissue oxidative damage in trahira, Hoplias malabaricus

This study investigated the effect of microcystin-LR (MC-LR) on in vivo cardiorespiratory function and on tissue biomarkers of oxidative stress in gills and liver of the trahira, a neotropical freshwater fish. Trahira were treated with an intraperitoneal injection of 100 µg MC-LR.kg^-1 body mass or a saline, with the toxic effects of MC-LR then evaluated after 48 h. Rates of oxygen uptake (V̇O₂) did not differ significantly between Control and the exposed group (Mcys), but exposure to MC-LR significantly reduced O₂ extraction in the Mcys group at all O₂ tensions. This was associated with higher gill ventilation volume (V̇_G) in the Mcys group at all O₂ tensions except 140 and 120 mmHg, and a higher tidal volume (V_T) of the Mcys group at all tensions except 140 mmHg. Heart rate was also higher in the Mcys group, significantly so at an O₂ tension of 40 mmHg. In the liver of trahira, exposure to MC-LR has significant effects on antioxidant defense systems, inducing a significant increase in the activity of the (GPx) glutathione peroxidase enzyme (100%) and in the reduced glutathione (GSH) content (70%) compared to the control group, but no effects on superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) enzymes. The liver showed no oxidative damage, when measured as lipid peroxidation (LPO) levels and protein carbonyl (PC) content. In the gills SOD and GPx enzyme activity increased significantly in the Mcys group (98% and 73% respectively) compared to the controls, although GSH, CAT and GST did not differ between groups. There was also no significant difference in GSH in this tissue. Levels of lipid peroxidation in the gills were 53% higher in the Mcys group, although carbonyl protein levels did not differ. In conclusion, these data show that MC-LR leads to development of hyperventilation and increased activity of the detoxification system and that this species was able to compensate the deleterious effects of microcystin on its vital functions. The antioxidant defense in the liver was able to contain the propagation of LPO and prevent the oxidation of proteins, although the gills of the fishes exposed to MC-LR were not able to contain the formation of reactive oxygen species and LPO, which led to the establishment of oxidative stress which impaired gill function.

Effects of subchronic manganese chloride exposure on tambaqui (Colossoma macropomum) tissues: oxidative stress and antioxidant defenses

This study aimed to evaluate oxidative stress parameters in juvenile tambaqui (Colossoma macropomum) exposed to 3.88 mg l(-1) Mn(2+) for 96 hours. Biomarkers of oxidative stress, such as thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST) activities, as well as content of reduced glutathione (GSH), were analyzed in gill, liver, brain, and kidney. The presence of Mn(2+) in the water corresponded to increased levels of Mn(2+) accumulation according to the following sequence: gill > kidney > brain > liver. There was a significant increase in TBARS levels (40 %) and SOD activity (80 %) in addition to a significant decrease in GSH content (41 %) in gills of fish exposed to waterborne Mn(2+). In hepatic tissue of the exposed animals, TBARS levels decreased significantly (35 %), whereas SOD (82 %) and GST activities (51 %) as well as GSH content (43 %) increased significantly. In brain of exposed juvenile fish, only significant decreases in SOD (32 %) and CAT activities (65 %) were observed. Moreover, the kidney of exposed fish showed a significant increase in TBARS levels (53 %) and a significant decrease in SOD activity (41 %) compared with the control. Thus, the changes in biomarkers of oxidative stress were different in the tissues, showing a specific toxicity of this metal to each organ.

Copper and the herbicide atrazine impair the stress response of the freshwater fish Prochilodus lineatus

In order to evaluate the effects of copper and atrazine on the stress response of the freshwater fish Prochilodus lineatus, juvenile fish were pre-exposed to copper (20 μg L(-1)) or atrazine (10 μg L(-1)) for 24 h and then submitted to air exposure for 3 min. Simultaneously fish kept in dechlorinated water for 24 h were subjected to air exposure and a non-stress group was not subjected to air stress or any contaminants. Animals were sampled immediately (t0) and after 1, 3 and 6 h of air exposure (t1, t3 and t6 respectively) for the analysis of plasma cortisol, glucose and Na(+), hepatic glycogen, branchial Na(+)/K(+)-ATPase (NKA), number of red blood cells per cubic millimeter of blood (RBC), hematocrit (Hct) and hemoglobin content (Hb). In fish pre-exposed to copper the stress response was inhibited, and at t1 and t3 both cortisol and glucose remained significantly lower compared to fish subjected to air stress only. In fish pre-exposed to atrazine there was no rise in cortisol, but there was an increase in plasma glucose, RBC, Hct and Hb at t0 and a return of these parameters to basal levels at t1, as they did not differ significantly in relation to non-stressed fish. Animals pre-exposed to either Cu or atrazine showed a significant reduction in NKA activity at t1 and t3, in relation to air stressed fish. These results clearly indicate that copper and atrazine impair cortisol stress response of P. lineatus and that fish subjected to a contaminant-induced stress, either by copper or atrazine, may not be able to respond to any additional stressors.

Interspecific variation of warning calls in piranhas: a comparative analysis

Fish sounds are known to be species-specific, possessing unique temporal and spectral features. We have recorded and compared sounds in eight piranha species to evaluate the potential role of acoustic communication as a driving force in clade diversification. All piranha species showed the same kind of sound-producing mechanism: sonic muscles originate on vertebrae and attach to a tendon surrounding the bladder ventrally. Contractions of the sound-producing muscles force swimbladder vibration and dictate the fundamental frequency. It results the calling features of the eight piranha species logically share many common characteristics. In all the species, the calls are harmonic sounds composed of multiple continuous cycles. However, the sounds of Serrasalmus elongatus (higher number of cycles and high fundamental frequency) and S. manueli (long cycle periods and low fundamental frequency) are clearly distinguishable from the other species. The sonic mechanism being largely conserved throughout piranha evolution, acoustic communication can hardly be considered as the main driving force in the diversification process. However, sounds of some species are clearly distinguishable despite the short space for variations supporting the need for specific communication. Behavioural studies are needed to clearly understand the eventual role of the calls during spawning events.

Ecological impacts of pesticides on Astyanax jacuhiensis (Characiformes: Characidae) from the Uruguay river, Brazil

Brazilian freshwater ecosystems are continuously exposed to pesticides and domestic sewage. The Uruguay River was chosen for this study because of its international importance, as it flows through Brazil, Argentina, and Uruguay. It receives contaminants such as pesticides and domestic residues. Thus, the aim of this study to assess the accumulation of pesticides in muscle of the fish Astyanax jacuhiensis, its biochemical responses, and the presence of pesticides in water. In total, seven pesticides were registered in water from both river sites. Eight pesticides were detected in fish muscle. The biochemical responses showed that brain lipid peroxidation (LPO) and protein carbonyl (PC) in A. jacuhiensis were higher in the summer. Muscle showed the highest LPO levels in the spring and the highest PC in the summer. Liver LPO and PC levels were higher in the spring and summer. In the gills, the PC was higher in the spring and the LPO in the spring and winter. In the brain and in the gills, glutathione-S-transferase activity was high in the summer and autumn. Catalase activity was lower during the winter and spring. Non-protein thiol (NPSH) levels were lower in the brain in the winter and spring. Muscle tissue showed lower NPSH in the winter (site 1). Liver NPSH showed increased levels in liver in the spring and winter (site 2). The biochemical results clearly is related to pesticides and/or to the presence of other contaminants in the water such as metals or domestic sewage. The accumulation of pesticides in fish muscle added evidence that pesticides have been used in the area surrounding the Uruguay River. In conclusion, the biomarkers assayed in the present study could be used in future investigations considering other sampling sites along Uruguay River.

Biochemical and behavioral responses of the Amazonian fish Colossoma macropomum to crude oil: the effect of oil layer on water surface

The largest Brazilian terrestrial province of petroleum mining is located at the margins of Urucu River, Amazonas. Mined crude oil is transported along 400 km across Solimões River to be refined in Manaus. Thus, the main goal of this study was to evaluate the effects of crude oil exposure on biochemical, physiological and behavioral parameters of juveniles of the Amazonian fish tambaqui (Colossoma macropomum). The toxicity of water-soluble and insoluble oil fractions and the influence of a layer formed by the oil on the water surface from low and high concentrations of crude oil were analyzed. The results showed a strong physical effect of oil at the water surface and a significant effect on fish behavior. Swimming time and response to alarm substance decreased when fish was exposed for just one day to water insoluble fraction, and remain lower after 30 days of exposure, compared to control. Chronic exposure to water insoluble fraction of the inert oil also affected these two parameters. Critical swimming velocity decreased in fish exposed to both crude and inert oil water insoluble fraction. These reductions are possibly related to a decrease in aerobic capacity. Only exposure to high concentrations of petroleum water-soluble fractions induced transient alterations of the analyzed parameters. The exposure of fish to low and high concentrations of water insoluble fraction of Urucu oil caused a reduction of responses to alarm substance, spontaneous swimming activity and swimming capacity (Ucrit), decreased activity of acetylcholinesterase, and increased activity of alkaline phosphatase. Severe hypertrophy of lamellar epithelium and extensive lamellar fusion of the gills were also observed. Overall, these results show significant behavioral and physiological changes caused by the oil layer on the water surface, which means that toxicity of petroleum produced by its chemical components is, in fact, in this fish species, enhanced by the presence of an oil phase as a physical barrier.

Potamodromous migrations in the Magdalena River basin: bimodal reproductive patterns in neotropical rivers

Magdalena River basin potamodromous fishes have two annual reproductive seasons: the subienda in the first half of the year and the mitaca in the second. Both upstream migrations are c. 30-45 days long; after that, with the onset of the rainy season, fishes spawn and remain in the river (resident individuals) or start a downstream movement (the bajanza) to return to the Magdalena floodplain lakes (nursery, shelter and feeding grounds). Due to their particular gonad development the bocachico Prochilodus magdalenae and probably the comelón Leporinus muyscorum are physiologically able to undertake two annual basin migrations. In the presence of dams or hydropower structures, fishes are able to find alternative migration routes. Some species should be re-classified in their migratory behaviour.

The transition from water-breathing to air-breathing is associated with a shift in ion uptake from gills to gut: a study of two closely related erythrinid teleosts, Hoplerythrinus unitaeniatus and Hoplias malabaricus

The evolutionary transition from water-breathing to air-breathing involved not only a change in function of the organs of respiratory gas exchange and N-waste excretion, but also in the organs of ion uptake from the environment. A combination of in vivo and in vitro techniques was used to look at the relative importance of the gills versus the gut in Na(+), Cl(-), and K(+) balance in two closely related erythrinid species: a facultative air-breather, the jeju (Hoplerythrinus unitaeniatus) and an obligate water-breather, the traira (Hoplias malabaricus). The jeju has a well-vascularized physostomous swimbladder, while that in the traira is poorly vascularized, but the gills are much larger. Both species are native to the Amazon and are common in the ion-poor, acidic blackwaters of the Rio Negro. Under fasting conditions, the traira was able to maintain positive net Na(+) and Cl(-) balance in this water, and only slightly negative net K(+) balance. However, the jeju was in negative net balance for all three ions and had lower plasma Na(+) and Cl(-) concentrations, despite exhibiting higher branchial Na(+), K(+)ATPase and v-type H(+)ATPase activities. In the intestine, activities of these same enzymes were also higher in the jeju, and in vitro measurements of net area-specific rates of Na(+), Cl(-), and K(+) absorption, as well as the overall intestinal absorption capacities for these three ions, were far greater than in the traira. When acutely exposed to disturbances in water O2 levels (severe hypoxia ~15% or hyperoxia ~420% saturation), gill ionoregulation was greatly perturbed in the traira but less affected in the jeju, which could "escape" the stressor by voluntarily air-breathing. We suggest that a shift of ionoregulatory capacity from the gills to the gut may have occurred in the evolutionary transition to air-breathing in jeju, and in consequence branchial ionoregulation, while less powerful, is also less impacted by variations in water O2 levels.

The effect of cryoprotectant agents on DNA methylation patterns and progeny development in the spermatozoa of Colossoma macropomum

DNA methylation patterns are inherited from parents and are imperative for proper embryonic development; however, alterations in these patterns can compromise fertilization and development into a fully functioning adult animal because DNA methylation is part of a complex program of gene transcription. In this study, we investigated the impact of cryoprotectant agents (CPAs) on DNA methylation patterns in spermatozoa and the consequences on embryonic development and the survival rate of progeny. Global methylation was assessed by enzymatic reactions in Colossoma macropomum spermatozoa that were cryopreserved using dimethylsulfoxide, dimethylformamide, methanol, ethyl glycol and glycerol as CPAs. Fertilization was carried out to evaluate survival rates and abnormalities in embryonic development upon treatment with each of the CPAs. Fresh semen served as the control. Our results indicated that, compared to the control group, spermatozoa cryopreservation decreased the fertilization rate and delayed embryonic development from the midblastula stage. Furthermore, spermatozoa cryopreserved in all CPAs had lower methylation levels and exhibited more delays and abnormalities during embryonic development than did fresh semen. Methanol resulted in fertilization, hatching rates and embryonic development that were closer to the control but had lower methylation levels. In conclusion, ours results show significant alterations on spermatozoa DNA methylation patterns caused by CPAs that are used in the semen cryopreservation process. DNA methylation pattern alterations affected the viability of progeny (r=0.48); however, these effects can be minimized by choosing the CPA that will compose the freezing solution.

Two sides of a coin: Effects of climate change on the native and non-native distribution of Colossoma macropomum in South America

Climate change and species invasions interact in nature, disrupting biological communities. Based on this knowledge, we simultaneously assessed the effects of climate change on the native distribution of the Amazonian fish Colossoma macropomum as well as on its invasiveness across river basins of South America, using ecological niche modeling. We used six niche models within the ensemble forecast context to predict the geographical distribution of C. macropomum for the present time, 2050 and 2080. Given that this species has been continuously introduced into non-native South American basins by fish farming activities, we added the locations of C. macropomum farms into the modeling process to obtain a more realistic scenario of its invasive potential. Based on modelling outputs we mapped climate refuge areas at different times. Our results showed that a plenty of climatically suitable areas for the occurrence of C. macropomum occurrence are located outside the original basins at the present time and that its invasive potential is greatly amplified by fish farms. Simulations of future geographic ranges revealed drastic range contraction in the native region, implying concerns not only with respect to the species conservation but also from a socio-economic perspective since the species is a cornerstone of artisanal and commercial fisheries in the Amazon. Although the invasive potential is projected to decrease in the face of climate change, climate refugia will concentrate in Paraná River, Southeast Atlantic and East Atlantic basins, putting intense, negative pressures on the native fish fauna these regions. Our findings show that short and long-term management actions are required for: i) the conservation of natural stocks of C. macropomum in the Amazon, and ii) protecting native fish fauna in the climate refuges of the invaded regions.

The role of ovarian steroids in reproductive plasticity in Hoplias malabaricus (Teleostei: Characiformes: Erythrinidae) in tropical reservoirs with different degrees of pollution

Chemicals in aquatic environments may lead to impairment of fish reproduction, but some species display plasticity levels to survive and reproduce in such localities. We investigated the reproductive cycle in a teleost species, Hoplias malabaricus, which inhabits a variety of environments with different degrees of pollution. Adult females were sampled at two locations in São Paulo State (Brazil), the reference Ponte Nova (PN) reservoir and the polluted Billings (BIL) reservoir. Metabolic and endocrine processes were analyzed throughout the annual cycle with special attention to ovarian histology, gonadosomatic index (GSI), fecundity, ovarian energetic substrates and plasma steroids analyses, in addition to physical and chemical analyses of the water. Pollutants were frequent in BIL but not in PN. The GSI, including the predominance of vitellogenic oocytes, was higher in spring and summer in both locations, but the oocyte recruitment dynamics was different. During winter, females from BIL presented vitellogenic oocytes and high levels of 11-ketotestosterone, which indicated precocity in the vitellogenic phase in relation to the females from PN. In animals from PN, high deposition of lipids occurred in the ovaries. However, plasma estradiol levels did not vary throughout the annual cycle. In animals from BIL, plasma estradiol levels peaked during the summer, but the ovarian lipid content remained unchanged throughout the year. The data suggest that the presence of pollutants cause various endocrine and metabolic responses and especially affects reproductive plasticity, which could explain why H. malabaricus survives under unfavorable environments.

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.

How will farmed populations of freshwater fish deal with the extreme climate scenario in 2100? Transcriptional responses of Colossoma macropomum from two Brazilian climate regions

Tambaqui (Colossoma macropomum Cuvier, 1818) is an endemic fish of the Amazon and Orinoco basins, and it is the most economically important native species in Brazil being raised in five climatically distinct regions. In the face of current global warming, environmental variations in farm ponds represent additional challenges that may drive new adaptive regional genetic variations among broodstocks of tambaqui. In an experimental context based on the high-emission scenario of the 5th Intergovernmental Panel on Climate Change (IPCC) report, we used two farmed tambaqui populations to test this hypothesis. RNA-seq transcriptome analysis was performed in the liver of juvenile tambaqui from northern (Balbina Experimental Station, Balbina, AM) and southeastern (Brumado Fish Farming, Mogi Mirim, SP) Brazilian regions kept for 30 days in artificial environmental rooms mimicking the current and extreme climate scenarios. Three Illumina MiSeq runs produced close to 120 million 500 bp paired-end reads; 191,139 contigs were assembled with N50 = 1595. 355 genes were differentially expressed for both populations in response to the extreme scenario. After enrichment analysis, each population presented a core set of genes to cope with climate change. Northern fish induced genes related to the cellular response to stress, activation of MAPK activity, response to unfolded protein, protein metabolism and cellular response to DNA damage stimuli. Genes biologically involved in regulating cell proliferation, protein stabilisation and protein ubiquitination for degradation through the ubiquitin-proteasome system were downregulated. Genes associated with biological processes, including the cellular response to stress, MAPK cascade activation, homeostatic processes and positive regulation of immune responses were upregulated in southeastern fish. The downregulated genes were related to cytoskeleton organisation, energy metabolism, and the regulation of transcription and biological rhythms. Our findings reveal the signatures of promising candidate genes involved in the regional plasticity of each population of tambaqui in dealing with upcoming climate changes.