Digest: Habitat and competition drive diversification in Gondwanan fish

Why do some clades diversify more than others? And what are the roles of abiotic and biotic factors in driving such unequal diversification? To explore this, Burns et al. (2024) investigate variation in body morphology in a group of freshwater fish, Characiformes, across South America and Africa. They find that habitat features such as slope, elevation, and flow rates have played a major role in the diversification of morphological variation in the Characiformes. The Neotropical lineages residing in significantly more diverse slope and elevation habitats were found to display more body shape diversity than African lineages. The authors also report that competition might have limited the morphological variation in African Characiformes compared to the Neotropical lineages. This study highlights the importance of exploring both abiotic and biotic factors when examining diversification.

Carbohydrate tolerance in Amazon tambaqui (Colossoma macropomum) revealed by NMR-metabolomics - Are glucose and fructose different sugars for fruit-eating fish?

In the present study, two approaches were followed to evaluate the metabolic responses of tambaqui (Colossoma macropomum), a frugivorous species, to intraperitoneal (IP) administration of glucose (GLU) and fructose (FRU) in fed (FED) and 10-day fasted (FAST) fish. Glucose and fructose tolerance tests were performed to assess the carbohydrate utilization and complementary NMR-metabolomics analyses were done to elucidate the impacts of sugar mobilization on the metabolic profile of plasma, liver and muscle. Blood was sampled from FED groups at 0, 3, 6 and 24 h; and at 0 and 24 h from FAST groups. Significant differences were observed in the hyperglycaemic peak between sugars at 3 h (GLU - 13.7 ± 2.0 mM vs. FRU - 8.7 ± 1.1 mM; saline 6.3 ± 0.6 mM) and on the return to normoglycaemia (GLU - 8.5 ± 2.2 mM vs. FRU - 5.2 ± 0.9 mM; saline 4.9 ± 0.6 mM) 6 h after IP on the FRU fish. The NMR-metabolomics approach allowed to conclude that tambaqui seems to be more responsive to the feeding regime (FED vs. FAST) than to the injected sugar (FRU vs. GLU). From the studied tissues, plasma showed no significant variations between feeding regimes at 24 h after IP, while muscle and liver revealed some variations on the final metabolome profile between FED and FAST groups. The metabolome variations between feeding regimes are indicative of changes on the amino acid utilization. Fish from FAST group seem to utilize amino acids as energy source rather than for protein synthesis and muscle growth. Variations on glucose concentration in muscle can also indicate different utilization of the sugars depending on the feeding regime.

Acoustic homogeneity in the piranha Serrasalmus maculatus

Different studies suggest some social calls could be used in fish identification if their specificity is unambiguously assessed. Sounds of different populations of piranhas Serrasalmus maculatus Kner, 1858 were recorded to determine their homogeneity between rivers inside a single basin (Araguari and Grande River, upper Paraná River basin) and between separated basins (Amazon and Paraná basins). All fish from the different populations produced sounds with similar acoustic features. Consequently, the populations were not discernible based on individual sound characteristics. This high homogeneity between sounds from different populations indicates their usefulness for conservation projects using passive acoustic monitoring in piranhas. Moreover, it supports the use of acoustic features as complementary key characteristics in taxonomic studies.

Eugenol induces body immobilization yet evoking an increased neuronal excitability in fish during short-term baths

Several studies have suggested eugenol as a suitable anaesthetic for fish. However, it has also been regarded as a toxic and aversive substance to several aquatic organisms, including fish. This study sought to assess the eugenol-induced behavioural alterations and its seizurogenic potential to fish. Moreover, a distinctive methodology for an in vivo evaluation of the brain activity was also presented. Prior to the evaluation of eugenol-induced responses, fish were exposed to pentylenetetrazole (PTZ), to characterize any seizure-like patterns. Antagonizing responses to PTZ were assessed in fish receiving diazepam (BDZ) and subsequently exposed to PTZ. Tambaqui fish juveniles, Colossoma macropomum (15.8 ± 2.8 g) were used as models and assayed as follows: (i) fish exposed to PTZ (15 mM) and (ii) fish receiving a dose of BDZ (10 mg Kg^-1) and later exposed to PTZ (15 mM) (BDZ-PTZ group). Thereafter, fish were evaluated throughout (iii) eugenol exposure at 65 μL L^-1 (ethanolic solution) and recovery. Control fish and a vehicle control group (ethanol at 585 μL L^-1) were also established. PTZ baths elicited body immobilization preceded by hyperactivity in a stereotyped seizure-like behaviour with increased EEG wave amplitude and frequency. PTZ effects in the brain were attenuated by a pre-administration of BDZ. Upon eugenol exposure, tambaqui had an intense neuronal excitability, showing a clonus-like seizure behaviour, also corroborated by the EEG patterns, which were consistent with a seizure-like response. Responses of eugenol-exposed fish resembled those of the PZT-exposed animals, with epileptiform discharges. EMG was in line with the EEG modulation, showing increased tracing oscillations and higher mean amplitudes in PTZ-exposed fish whereas in BDZ-PTZ group muscle contraction was less frequent and powerful. Fish exposed to eugenol showed initially some muscle activity followed by a loss of muscle tonus over time. In summary, our results showed that upon eugenol exposure, although a time-dependent body immobilization was attained, fish presented an intense neuronal excitability comparable to that evoked by PTZ. Eugenol failed to promote depression of the CNS and therefore may be not suitable to be used for general anaesthesia of C. macropomum. As eugenol could be implicated in seizurogenesis and be potentially toxic to the fish brain, protocols suggesting the broad use of eugenol for short-term anaesthesia or euthanasia of fish should be carefully revised, as it raises important concerns in terms of ethics and fish welfare.

Integrated use of biomarkers to evaluate the reproductive physiology of Astyanax fasciatus and Hoplias malabaricus males (Teleostei: Characiformes) in polluted reservoirs

The reproductive physiology of fish can be changed by the presence of pollutants in the water, which act as endocrine disrupting compounds (EDC). We evaluated the impacts of water contaminants in polluted reservoirs acting as possible EDC on the reproductive physiology of Astyanax fasciatus and Hoplias malabaricus males. We used biomarkers with different levels of biological organization. Hoplias malabaricus adult males were collected in the summer and winter at five different sites in the Tietê River Basin: the Ponte Nova reservoir (PN), considered a reference site due to the low anthropogenic influence; the Billings reservoir (BIL) at two different branches; and the Guarapiranga reservoir (GUA) at two different branches. Astyanax fasciatus adult males were collected at PN and BIL. BIL and GUA are subjected to great anthropogenic action. We analyzed gonadal histomorphology, testosterone (T), 11-ketotestosterone (11-KT), estradiol (E₂) plasma levels, and gene expression of hepatic vitellogenin (vtgA) and pituitary follicle stimulating hormone (fshβ). In the PN reservoir (reference), the biomarkers analyzed in both species did not differ between the periods analyzed. This is an evidence that the animals keep the same reproductive activity during both seasons. The changes in the plasma concentration of gonadal steroids in both species in polluted reservoirs suggest the presence of EDC compounds in the water and/or adjusts of the physiological setpoint to allow the reproduction in such adverse conditions. The use of vtgA as biomarker suggests the presence of estrogenic compounds, mainly in BIL, but with a more evident response of H. malabaricus. However, even considering physiological changes, both species present testes during the maturation phase that allow the reproduction in an environment with a high degree of pollution.

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.

Yellow-eyed piranhas produce louder sounds than red-eyed piranhas in an invasive population of Serrasalmus marginatus

Serrasalmus marginatus is a piranha species native from the lower Paraná River basin and has been invasive in the upper Paraná River basin since the 1980s. In piranhas, sounds of different species have different features. The aim of this study was to investigate if the sounds produced by this species could be used to distinguish two morphotypes: red- and yellow-eyed S. marginatus from the Araguari River (upper Paraná River basin). All the temporal and frequency features of the sounds were equivalent in both groups of eye colour; it corresponds to the species-specific signature described for S. marginatus. Nonetheless, the amplitude features were all statistically different between red- and yellow-eyed piranhas. Yellow-eyed specimens produced louder sounds. In different fish species, colour change in eyes can be due to the absence or the presence of a dominant allele. It can also be involved in social rank or during reproduction. Different hormones and neuropeptides can modulate vocal features. It is hypothesized that a mutation or different hormonal concentrations could explain both sound amplitude and eye colour playing a role in animal communication in S. marginatus.

Aerobic Metabolism Impairment in Tambaqui (Colossoma macropomum) Juveniles Exposed to Urban Wastewater in Manaus, Amazon

The main purpose of the present study was to investigate the potential use of metabolic parameters as non-specific biomarkers of pollution. The Igarapé do Quarenta is a small urban river crossing an industrial area in the city of Manaus, Amazon, and receives the city wastewater without treatment. The fish tambaqui (Colossoma macropomum) were exposed to water collected from two different sites of that stretch for 96 h. After exposure, routine metabolic rate (RMR) was measured, and fish were euthanized for measurements of electron transport system (ETS) activity, Copper (Cu) and Cadmium (Cd) bioaccumulation and biliary PAHs. Water in the sampling points presented low oxygen and high pH, conductivity, dissolved ions, Cu, Cd and ammonia. Bile concentrations of PAHs were high suggesting industrial pollution. The tambaqui exposed to water from Igarapé do Quarenta showed increased RMR and decreased ETS/RMR suggesting impairment of metabolic fish performance and the potential use of these parameters as biomarkers.

Use of bioacoustics in species identification: Piranhas from genus Pygocentrus (Teleostei: Serrasalmidae) as a case study

The genus Pygocentrus contains three valid piranha species (P. cariba, P. nattereri and P. piraya) that are allopatric in tropical and subtropical freshwater environments of South America. This study uses acoustic features to differentiate the three species. Sounds were recorded in P. cariba, two populations of P. nattereri (red- and yellow-bellied) and P. piraya; providing sound description for the first time in P. cariba and P. piraya. Calls of P. cariba were distinct from all the other studied populations. Red- and yellow-bellied P. nattereri calls were different from each other but yellow-bellied P. nattereri calls were similar to those of P. piraya. These observations can be explained by considering that the studied specimens of yellow-bellied P. nattereri have been wrongly identified and are actually a sub-population of P. piraya. Morphological examinations and recent fish field recordings in the Araguari River strongly support our hypothesis. This study shows for the first time that sounds can be used to discover identification errors in the teleost taxa.

Implications of the movement behaviour of African tigerfish Hydrocynus vittatus for the design of freshwater protected areas

African tigerfish Hydrocynus vittatus (n = 35) were tagged with external radio-transmitters in the Kavango River, Namibia, to determine whether freshwater protected areas could be an effective tool for the management and conservation of this species. They were manually tracked in the core study area of 33 km every c. 12 days from July-October 2016 to May 2017 for between 123 to 246 days. In addition, 14 extended surveys were carried out for up to 680 km to determine the total area use of the tagged individuals. Tigerfish displayed at least two behavioural patterns either having high site fidelity with shorter movements or using larger areas with longer movements. Twenty-three (66%) of the tigerfish had high site fidelity using an area of less than 33 km of river, whereas 12 tigerfish (34%) undertook long distance movements of up to 397 km upstream and 116 km downstream from their tagging locations. During the long-distance movements tigerfish crossed the territorial boundaries of Angola, Namibia and Botswana. Of the 35 fish that were monitored, 14 (40%) spent more than 80% of the monitored time in the 33 km study area and 18 (51%) stayed within the study area for at least 50% of the monitored time. These findings suggest that freshwater protected areas may be a useful management tool and we predict that a protected river area of 2-5 km river length could protect 25.9-34.6% of the population for at least 75% of the time whereas protection of 10 km river length could protect at least 50% of tigerfish for at least 75% of the time.

Biotransformations, Antioxidant System Responses, and Histopathological Indexes in the Liver of Fish Exposed to Cyanobacterial Extract

Radiocystis fernandoi, a microcystin (MC) producer, has been common in cyanobacterial blooms in tropical regions. Microcystin is a hepatotoxin that causes tissue damage and even death in animals, including humans; its detoxification process may involve biotransformation and activation of the antioxidant defense system. We evaluated the detoxification pathway, examined the antioxidant defense system responses, and determined the alterations and the organ histopathological indexes in the liver of the tropical fish Hoplias malabaricus after acute and subchronic intraperitoneal exposure to microcystin. The crude microcystin extract of R. fernandoi had predominantly MC-RR and MC-YR. The detoxification process was activated by increasing ethoxyresorufin-O-deethylase activity, whereas glutathione S-transferase was inhibited. The activity of the antioxidant defense enzymes superoxide dismutase (SOD) and glutathione peroxidase decreased after acute exposure; the SOD-catalase system and the glutathione level increased after subchronic exposure. The carbonyl protein level, lipid peroxidation (LPO), and DNA damage were unchanged after acute exposure, whereas protein carbonyl was unchanged, LPO decreased, and DNA damage increased after subchronic exposure. Histopathological alteration indexes differed between acute and subchronic exposure, but the histopathological organ indexes indicate liver dysfunction in both exposure periods. We conclude that MC-RR and MC-YR induce different liver responses depending on the time of exposure, and the antioxidant defense responses after subchronic exposure may help to partially restore the liver function. Environ Toxicol Chem 2020;39:1041-1051. © 2020 SETAC.

β-Glucan enhances respiratory activity of leukocytes suppressed by stress and modulates blood glucose levels in pacu (Piaractus mesopotamicus)

We evaluated the immune response of pacu fed with a β-glucan diet (0.5%) for 10 days. After the feeding period, fish were subjected to handling and 3 h after, inoculated with Aeromonas hydrophila. Fish were sampled before handling (baseline condition), 3, 6, and 24 h and 1 week after inoculation. A higher level of blood glucose was found in fish treated with β-glucan in baseline conditions. Handling and bacterial inoculation increased the circulating levels of cortisol and glucose and promoted the acute inflammatory response (lymphopenia and neutrophilia). β-Glucan prevented the decrease in the respiratory activity of leukocytes observed in the control group at 3 h sampling. β-Glucan did not affect the complement and lysozyme, which were activated 24 h after the bacterial challenge in control fish. A reduction in the number of leukocytes was found in fish treated with β-glucan 1 week after the challenge. We suggest two plausible hypotheses for this event: (1) it could be attributed to a depletion of the immune responses or (2) it could be due to a mobilization of the leukocytes to the spleen for antigen presenting/processing. In general, β-glucan avoided the reduction of the activity of leukocytes after stress and the bacterial challenge and increased the baseline glucose levels. Our findings confirm the immunomodulatory action of glucan and add evidence showing that glucan can have a role in stress response.

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.

Impact of activation solutions on fresh and frozen-thawed sperm motility and fertilization success for two species of migratory freshwater fishes

Extracellular environment conditions, ionic concentration, pH, osmolality, and temperature influence sperm activation and sperm quality. The aim of this study was to evaluate the effects of different activating solutions on sperm quality and fertilization rate of fresh and post-thaw sperm in Brycon orbignyanus and Prochilodus vimboides. Activation solutions with ions: NaCl, KCl, CaCl₂ (150 mOsm kg^-1), without ions: glucose (150 mOsm kg^-1) and water: reverse osmosis (RO) (∼0 mOsm kg^-1) and tank water (TW) were tested. In experiment 1, fresh sperm motility was activated in each activating solution and motility rate (%), motility quality score (0-5), and motility duration (seconds) were subjectively evaluated using a microscope. In experiment 2, sperm was cryopreserved and post-thaw sperm quality was assessed in each activating solution. Methyl glycol was used as cryoprotectant and for B. orbignyanus a solution of BTS® 5% in water reverse osmosis - 325 mOsm kg^-1 was used as extender, while for P. vimboides it was used a solution of glucose 5% in water reverse osmosis - 325 mOsm kg^-1. In straw, cryoprotectant, extender, sperm were respectively 10%, 80% 10% (V/V). B. orbignyanus fresh sperm activated in NaCl, KCl, glucose solutions, TW and RO yielded higher averages for all the subjective parameters analysed. In fresh sperm of P. vimboides the highest values were observed when glucose solution was used for sperm motility activation, and the highest fertilization rates were observed in samples activated in glucose or RO solutions. B. orbignyanus post-thaw sperm activated in TW (45.1%) or RO (39.7%) presented the highest values for motility. The highest values of curvilinear velocity (VCL) were observed using glucose (69.5 μm s^-1), NaCl (67 μm s^-1) and KCl (68.4 μm s^-1), but the highest fertilization rates were observed when glucose (3.6%), RO (3.5%) and TW (2.5%) were used. P. vimboides post-thaw sperm activated in glucose solution presented the highest motility rate (41%), VCL (43.7 μm s^-1), fertilization rate (18.2%) and hatching rate (13.7%). In order to achieve the best seminal quality, fertilization and hatching rates in both fresh and post-thaw sperm, the glucose solution, TW and RO are indicated for use as sperm motility activators in B. orbignyanus, whereas for P. vimboides the glucose solution and RO are indicated.

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.

Effects of pH on the incubation and early development of fish species with different reproductive strategies

Fish reproduction in natural environments tends to occur in conditions, including extreme pH values, ideal for the survival of offspring. In this context, the purpose of this study was to assess the influence of pH on both survival and early development of two fish species, Astyanax lacustris (short-distance migrating fish) and Piaractus mesopotamicus (long-distance migrating fish), with different reproductive strategies. Our experiments were divided into two tests (incubation and larviculture) at five pH levels. First was incubation through a water recirculation system using 2 L incubators followed by larviculture using a 2.5 L aquarium. pH had no influence on the hatching rate of A. lacustris eggs, but affected the yolk-sac diameter, while the newly-hatched larvae had some skeletal disorders. For P. mesopotamicus, pH influenced the hatching rate and perivitelline space, while the newly-hatched larvae had several skeletal disorders. The larviculture of A. lacustris revealed no effect on the survival rate, but the analyzed morphometric variables indicated significant differences between the treatments. An acidic pH negatively influenced the survival rate of P. mesopotamicus, and all morphometric variables also varied significantly between the treatments. We concluded that both the survival and development of A. lacustris and P. mesopotamicus revealed different responses at pH levels during incubation and larviculture tests.

Electrophysiological responses in Amazonian fish species Bryconops caudomaculatus (Osteichthyes: Characiformes) as biomarkers of xenobiotic toxicity

Sublethal exposures to environmental pollutants may cause changes in physiological parameters. Thus, knowledge of basal physiological rates of the species and the development of methods to quantify these rates are extremely important. Considering the scarcity of cardiac and muscle physiological studies in native Amazonian fish species and that no evaluation of electrophysiological responses by exposure to a stressor has been reported in Bryconops caudomaculatus, the aim of this study was to develop techniques of electromyographic and electrocardiographic recordings of normal responses, during toxicity induction and short-term recovery. A total of 9 animals were used, divided into two groups: control group (n = 4) and treated group (n = 5), with records lasting 5 min. The results showed that the basal electromyographic records indicate that the studied species has a very intense swimming activity, whereas the basal cardiac parameters clearly showed the patterns in P wave tracing, QRS complex, T wave and Q-T and R-R intervals. During exposure to the stressor, muscle activity ceased presenting intense decrease and myorelaxant effect expected. Electrocardiographic responses confirmed cardiotoxicity with intense bradycardia, ventricular bigeminism, prolongation of QRS complex duration and cardiac arrhythmias, indicating cardiac dysfunction. It was concluded that the electrophysiological responses are excellent biomarkers and showed the susceptibility of the species to the tested substance. In addition, the electrocardiogram and the electromyogram are excellent techniques to reflect the degree of environmental stress when organisms are exposed to toxic substances in the environment.

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.

Osmoregulatory disturbance in Neotropical fish exposed to the crude extracts of the cyanobacterium, Radiocystis fernandoi

Blooms of cyanobacteria, a common event in eutrophic environments, result in the release of potentially toxic substances into the water. The cyanobacterium Radiocystis fernandoi produces microcystin (MC) and other peptides that may disturb homeostasis. This study evaluated the effect of intraperitoneal injections containing the crude extract (CE) of R. fernandoi strain R28 on the gills and kidneys of neotropical fish, Piaractus mesopotamicus, 3, 6 and 24 h post-injection. CE contained MC-RR, MC-YR and minor other oligopeptides. Plasma ions and the activities of the enzymes PP1 and PP2A, Na⁺/K⁺-ATPase (NKA), H⁺-ATPase (HA) and carbonic anhydrase (CA) were determined and morphological changes in both the gills and kidneys were characterized. Compared to controls, the concentration of Na⁺ within the plasma of P. mesopotamicus decreased after treatment with CE 3 h post treatment and increased after 24 h; the concentration of K⁺ decreased after 6 h. The activity of the endogenous PP1 and PP2A was unchanged in the gills and was inhibited in the kidneys 6 h after i.p. injection. In the gills, NKA activity increased after 3 h and decreased 6 h post i.p. exposure. Further, NKA activity did not differ from the controls 24-h post injection. In the kidneys, NKA, HA and CA activities were unaffected by treatment. The mitochondria-rich cell (MRC) density in the gills decreased after 3 h in the filament and 3 and 6 h in the lamellae and was restored to the control levels 24 h post-exposure. Filament epithelial hyperplasia and hypertrophy, lamellar atrophy and rupture of the lamellar epithelium were the most common effects of treatment in the gills. No histopathological changes occurred in the kidneys. This study demonstrates that a single dose of toxic CE from R. fernandoi can cause a transitory ion imbalance in P. mesopotamicus which is related to the changes in MRC levels and NKA activity. Ionic balance was recovered 24 h post i.p. injection, however, morphological changes that occurred in the gills took a longer amount of time to return to normal. To conclude, the effects of components contained within the CE of R. fernandoi may be harmful to P. mesopotamicus. In particular, the recovery of ionic regulation depends on MRC responses and histopathological changes produced by CE may affect gas exchange and other gill functions.

Disturbance calls of five migratory Characiformes species and advertisement choruses in Amazon spawning sites

Species-specific disturbance calls of five commercially-important characiform species are described, the Curimatidae commonly called branquinhas: Potamorhina latior, Potamorhina altamazonica and Psectrogaster amazonica; Prochilodontidae: jaraquí Semaprochilodus insignis and curimatã Prochilodus nigricans. All species have a two-chambered swimbladder and the sonic mechanism, present exclusively in males, utilises hypertrophied red muscles between ribs that adhere to the anterior chamber. The number of muscles is unusually plastic across species and varies from 1 to 4 pairs suggesting considerable evolution in an otherwise conservative system. Advertisement calls are produced in river confluences in the Madeira Basin during the high-water mating season (January-February). Disturbance calls and sampling allowed recognition of underwater advertisement choruses from P. latior, S. insignis and P. nigricans. The advertisement calls of the first two species have largely similar characteristics and they mate in partially overlapping areas in the Guaporé River. However, P. latior sounds have a lower dominant frequency and it prefers to call from river confluences whereas S. insignis shoals occur mostly in the main river channel adjacent to the confluence. These results help identify and differentiate underwater sounds and evaluate breeding areas during the courtship of commercially important characids likely to be affected by two hydroelectric dams.

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.

Hemiodus bimaculatus, a new species of Hemiodontidae from the Rio Tapajós drainage, Brazil (Ostariophysi: Characiformes)

Hemiodus bimaculatus sp. nov., is described from tributaries of the Rio Juruena and Rio Teles Pires in the upper Rio Tapajós basin. The new species is diagnosed from most congeners, except Hemiodus jatuarana, by having a conspicuous circular or horizontally elongate dark blotch on the caudal peduncle (v. inconspicuous in H. iratapuru and absent in the other species). The new species differs from H. jatuarana by having a round midlateral spot on the flank (v. absent in H. jatuarana), 98-121 perforated scales in the lateral line (v. 66-72 in H. jatuarana), 23-28 scale series above and 14-19 below lateral line (v. 12-13 above and 6-7 below in H. jatuarana). Hemiodus bimaculatus is hypothesised to be related to species of the H. microlepis group, from which it also differs by having 11-25 epibranchial (v. 26-34 in H. argenteus, 29-39 in H. microlepis, 21-42 in H. orthonops and 27-35 in H. parnaguae) and 18-31 ceratobranchial (v. 38-50 in H. argenteus, 43-58 in H. microlepis, 32-52 in H. orthonops and 34-48 in H. parnaguae) gill rakers in the first arch.

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.

Antioxidant imbalance and genotoxicity detected in fish induced by titanium dioxide nanoparticles (NpTiO2) and inorganic lead (PbII)

Titanium dioxide nanoparticles (NpTiO₂) are the most widely-used nanoparticle type and the adsorption of metals such as lead (PbII) onto their surface is a major source of concern to scientists. This study evaluated the effects of the associated exposure to both types of contaminant, i.e., lead (a known genotoxic metal) and NpTiO₂, in a freshwater fish (Astyanax serratus) through intraperitoneal injection for an acute assay of 96 h. The effects of this exposure were evaluated using the comet assay, DNA diffusion assay and piscine micronucleus test, as well as the quantification of antioxidant enzymes (SOD, CAT, and GST) and metallothioneins. Our findings indicate that co-exposure of PbII with NpTiO₂ can provoke ROS imbalances, leading to DNA damage in the blood and liver tissue of A. serratus, as well as modifying erythropoiesis in this species, inducing necrosis and changing the nuclear morphology of the erythrocytes.

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).

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.

Larval development of Brycon amazonicus (Teleostei, Bryconidae) with a focus on locomotory, respiratory and feeding structures

In the present work we describe the larval development of Brycon amazonicus, with emphasis on structures linked to swimming, respiration and feeding. We monitored from larval hatching (13 h post-fertilization) to juvenile stage. Formation of the oral cavity and differentiation of gill arches began within 4 h post-hatching (hph) and within 11 hph the primordium of the pectoral fin appeared. At 25 hph, the head was in a rectilinear position with a terminal mouth, when the onset of tooth formation appeared. At 35 hph, gill arches were covered by the operculum and branchiostegal membrane and cusps of teeth pierced the epithelium of the premaxilla and anterior dentary region. Sharp teeth were observed in the maxilla at 171 hph and the pelvic fin primordium appeared at 243 hph, with taste buds on the tongue and the roof of the buccopharyngeal cavity. At 579 hph, all structures related to swimming and food capture were formed. Exogenous feeding of the larvae started at 29 hph, before the endogenous reserves were used up and the development of efficient swimming ability, reflecting the species' need to increasingly specialize on prey capture.

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.

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.

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.

Thermal tolerance of the invasive red-bellied pacu and the risk of establishment in the United States

Indigenous red-bellied pacu, Piaractus brachypomus, populations are in decline due to overfishing. Once ignored by aquaculturists because of their perceived low economic value, renewed aquaculture efforts in Central and South America aim to relieve fishing pressures on natural pacu populations. In the southern United States pacu aquaculture for the aquarium trade has raised concerns that accidental release could lead to establishment of overwintering populations outside captivity-a threat accentuated by the average 6 °C increase in shallow-water temperatures predicted by the end of the century. In the present study, Critical and Chronic Thermal Methodology was used to quantify red-bellied pacu thermal tolerance niche requirements. The data suggest that red-belllied pacu are a thermophilic species capable of tolerating low and high chronic temperatures of 16.5 °C and 35 °C, respectively. Critical thermal minimum and maximum temperatures of fish acclimated near their chronic limits are 10.3 and 44.4 °C. Red-bellied pacu aquaculture in the United States is concentrated in subtropical Florida regions that encourage rapid growth and reproduction, but carry an increased risk of establishing reproducing populations in local freshwater systems. The thermal niche data show that the risk of bioinvasion can be reduced or eliminated by adopting an approach whereby aquaculture potential is integrated with environmental temperature constraints.

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.

Glucan-MOS® improved growth and innate immunity in pacu stressed and experimentally infected with Aeromonas hydrophila

We tested the efficacy of a commercial product (Glucan-MOS^®) derived from yeast Saccharomyces cerevisiae, containing two combined products, β-1,3-1,6 glucans and mannans on the growth, feed efficiency, stress and innate immune responses of juvenile pacu (Piaractus mesopotamicus) after a stressful handling and bacterial inoculation. For this, we evaluated the serum cortisol and plasma glucose levels, the respiratory activity of leukocytes, the serum lysozyme levels, as well as the number of circulating erythrocytes and leukocytes of fish fed during 30 days with diets containing increased levels of Glucan-MOS (0.0, 0.1, 0.2, 0.4 and 0.8%). The supplementation of 0.1% improved weight gain, feed conversion and the protein efficiency ratio compared to a control diet. The 0.2 and 0.4% Glucan-MOS^® diets were sufficient to increase the respiratory burst of leukocytes and lysozyme activity, the number of thrombocytes, neutrophils and monocytes in the blood after a stressful handling and bacterial challenge, and minimized stress response as shown by decreased cortisol and glucose levels when compared to the control. The results of this work reinforce the benefits of the adoption of feeding strategies including combination of both β-1,3-1,6 glucans and mannans as a dietary supplement in periods prior to intensive management. The 30-day period was sufficient to stimulate growth performance, improve nutrient utilization, minimize stress response and modulate innate immunity responses.

Development of secondary sexual characters and their relationship to ontogeny and seasonal reproductive period in Hyphessobrycon igneus (Ostariophysi: Characiformes)

Sexual dimorphism in size, anal-fin shape and coloration of Hyphessobrycon igneus, Characidae, were examined. Males were more frequent at larger body sizes, confirming body size as a sexually dimorphic trait. Anal-fin shape and the colour of all fins were the same for females and juveniles, differing only in adult males. Likewise, only adult males had bony hooks on fin rays; larger and more sexually mature males had the most numerous and developed hooks and hooks were most developed in degree and number during peak reproductive periods. Fin hooks regressed in number and developmental degree after the reproductive period, but restarted development with the beginning of the new reproductive period without completely disappearing. Results show that bony hooks have a development and regression cycle related to reproductive seasonality.

Impact of waterborne and trophic mercury exposures on cardiac function of two ecologically distinct Neotropical freshwater fish Brycon amazonicus and Hoplias malabaricus

Metal pollutants have been considered one of the main factors underlying the depletion of biodiversity in natural populations unbalancing aquatic environments. The aim of this study was to evaluate the effects of exposure to inorganic Hg on myocardial contractility and the electrocardiogram (ECG) of two ecologically distinct Neotropical fish species, namely: matrinxã (Brycon amazonicus) and trahira (Hoplias malabaricus). Matrinxãs were exposed to a sublethal concentration of 0.1mgL^-1 of Hg in water for 96h. Trahiras were exposed to dietary Hg doses (0.45mg of Hg, each 4days, for 30days) using juvenile B. amazonicus as the prey vehicle. Hg exposures decreased myocardial isometric twitch force development, harmed contraction/relaxation dynamics and cardiac pumping capacity (CPC), and reduced the relative contribution of the calcium stored in the sarcoplasmic reticulum (SR) to excitation contraction (EC) coupling in both fish species. Analysis of the ECG revealed that Hg impaired electrical conduction across the heart, inducing first degree atrioventricular block and lengthening the plateau phase of action potential duration. In trahira trophic doses of Hg induced a marked bradycardia, increasing the duration of the ventricular action potential and delaying atrial and ventricular depolarization. These findings indicate that both acute and long-term Hg exposure, by different routes is cardiotoxic to matrinxã and trahira. Hg potently impaired intracellular calcium kinetics in the cardiomyocytes, myocardium contractility, and electrical conduction across the heart, all of which can be implicated in decreased cardiac output and putative heart failure.

Alternagin-C (ALT-C), a Disintegrin-Like Cys-Rich Protein Isolated from the Venom of the Snake Rhinocerophis alternatus, Stimulates Angiogenesis and Antioxidant Defenses in the Liver of Freshwater Fish, Hoplias malabaricus

Alternagin-C (ALT-C) is a disintegrin-like protein isolated from Rhinocerophis alternatus snake venom, which induces endothelial cell proliferation and angiogenesis. The aim of this study was to evaluate the systemic effects of a single dose of alternagin-C (0.5 mg·kg⁻¹, via intra-arterial) on oxidative stress biomarkers, histological alterations, vascular endothelial growth factor (VEGF) production, and the degree of vascularization in the liver of the freshwater fish traíra, Hoplias malabaricus, seven days after the initiation of therapy. ALT-C treatment increased VEGF levels and hepatic angiogenesis. ALT-C also enhanced hepatic antioxidant enzymes activities such as superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase, decreasing the basal oxidative damage to lipids and proteins in the fish liver. These results indicate that ALT-C improved hepatic tissue and may play a crucial role in tissue regeneration mechanisms.

Reproductive characteristics of pike-characids Boulengerella cuvieri (Ctenoluciidae) in the middle Xingu River, Eastern Amazon

This study evaluated the reproductive characteristics of pike-characids, Boulengerella cuvieri, during the hydrological cycle in the Xingu River, eastern Amazon. The sex ratio was 1:1 and the gonado-somatic index and relative frequency of maturation stages indicate a short breeding season of single phase spawning that coincides with a filling and flood period. Mean standard length at first sexual maturity for female B. cuvieri was estimated to be 22·9 cm.

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.

Acute fluoxetine treatment increases aggressiveness in juvenile matrinxã (Brycon amazonicus)

Fluoxetine (FLX) is a selective serotonin (5-HT) reuptake inhibitor known for its effects modifying aggressiveness, personality traits, and anxiety-like behaviors. The aim of the present study was to evaluate the influence of the acute treatment, by immersion, with FLX on aggressive behavior of resident Brycon amazonicus fish. Fish pretreated with FLX presented an increase in aggressiveness, evidenced by the increase on the number of bites and chases against the intruder and a decrease in latency for the first attack, when compared to control fish. Together with previous studies, these results show the complexity of the neural modulation of the aggressive behavior in fish by 5-HTergic system.

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.

[Basic biological parameters for Pseudocurimata lineopunctata (Characiformes, Curimatidae) conservation in the Anchicayá River of the Cauca Valley, Colombia]

Pseudocurimata lineopunctata represents an important nutritional source for local human communities in Colombia and Ecuador. Although the yearly catch of this fish is low (590 kg/year), there are no restrictions on minimum size, and this species is categorized as vulnerable with moderate extinction risk by the Regional Autonomous Corporation of the Cauca Valley (Colombia). To support conservation programs, biological data of the target species are required. Therefore, the aims of this study were to describe the sex ratio, distribution, size to weight ratio, macroscopic stages of reproductive maturity, fecundity, and size at first sexual maturity for P. lineopunctata. For this, fish samples were captured with nets over nine months (February-October) in 2007. The total length (Lt) of the captured fish ranged between 10.7 and 16.5 cm, with total weight (Pt) between 25.0 and 67.5 g. Females represented 52.6 % of the sample group while males represented 47.4 %, and differences in sex ratio were observed in relation to fish size. For all sampled months, the fish captured showed an advanced maturity state. Based on analyses of the gonadosomatic index (IGS), gonadic index (IG), and Fulton’s condition factor (K), and two spawning peaks were determined, one in June-July, and the other in September-October. The size at first sexual maturity was 9.2 cm for females and 10.1 cm for males. Absolute fecundity was estimated as 3 598 oocytes/g♀. It is necessary to carry out additional investigations on the reproduction of this species, to support future repopulation programs.

Characterization of gonadotropic cells during continuous and seasonal spermatogenesis of two freshwater fish species: a histochemical and immunohistochemical study

This work describes gonadotropic (GtH) cells and their morphological and immunohistochemical changes during the spermatogenic cycle of Serrasalmus maculatus (continuous spermatogenesis) and Pimelodus maculatus (seasonal spermatogenesis). GtH cells, widely distributed in the proximal pars distalis of the adenohypophysis, were characterized as round-shaped cells with eccentric nucleus, and cytoplasm with basophilic secretory granules and a variable number of vacuoles for both species. Immunohistochemistry against β-follicle-stimulating hormone (Fsh) and β-luteinizing hormone (Lh) in adjacent sections showed two separated GtH-producing cell populations, and a third population where both GtHs are expressed in the same cell for both species. In the seasonal spermatogenesis of P. maculatus, GtH cells seemed to be more abundant during developing and spawning capable phases. In contrast, no cyclic changes were detected in the continuous spermatogenesis of S. maculatus, except for the strong immunoreaction for Fsh and Lh in males with intense spermiogenesis. We conclude that changes reported here might reflect the type of spermatogenic cycle (seasonal or continuous) which are under different regulatory mechanisms (environmental and internal cues) controlling the reproduction in these species.

Canonical correlation analysis to identify the semen characteristics used to forecast the freeze survival of Curimba (Prochilodus lineatus) spermatozoa

　　OBJECTIVE: To identify which sperm characteristics were able to predict more accurately the quality of curimba (Prochilodus lineatus) semen upon freezing using canonical correlation analysis.

METHODS

Eleven fish breeders with initial mean weight of 705.21 ± 111 g were used. For cryopreservation, 200 µL of semen were taken from each animal and diluted in the cryoprotectant solution (10% dimethyl sulfoxide and 5% Beltsville Thawing Solution Minitub) in a 1:4 ratio and placed into 0.5-mL straws. Sperm characteristics (motility, sperm abnormalities, total antioxidant activity and lipid peroxidation) were evaluated. A randomized block design with duplicate samples per treatment (fresh and frozen semen) was used. The block factor was the animals, and the experimental unit the ejaculates. Canonical correlation was used to evaluate the association between sperm characteristics of fresh semen and thawed semen.

RESULT

There was a significant association (P = 0.10) among the variables measured in fresh semen with the variables measured in thawed semen, and 78.6% of the difference observed in the thawed semen can be attributed to variation of variables measured in fresh semen. Sperm motility, motility duration and antioxidant activity of the thawed semen showed an inverse relationship with those of the fresh semen; whereas the minor sperm abnormalities, major sperm abnormalities and lipid peroxidation showed a direct relationship with those of the fresh semen. Only the rate and motility duration of the thawed semen presented high correlation (-0.63 and -0.73, respectively) with the canonical variable represented by the sperm characteristics of fresh semen.

CONCLUSIONS

The rate and motility duration of fresh semen may be used to predict the quality of the thawed sperm in Prochilodus lineatus.

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.

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.

Fatty acid alterations in the detritivorous Prochilodus lineatus promoted by opportunistic feeding on sewage discharges in the Río de la Plata estuary

Muscle fatty acid profiles and PCB contents of the detritivorous species Prochilodus lineatus and its diet (stomach contents, settling particles and sediments) were analysed from reference and polluted areas of the Paraná-Rio de la Plata basin, to evaluate the alterations produced by opportunistic feeding on sewage discharges. Overall muscle fatty acid composition was dominated by saturated and monounsaturated 16 and 18 carbon (18 C-FA) components with reduced long-chain polyunsaturated fatty acids (LC-PUFA). Compared to sediments, settling particles and stomach contents were enriched in lipids and had a similar fatty acid composition. Opportunistic feeding on sewage detritus at Buenos Aires resulted in enhanced PCB and triglyceride accumulation, with higher proportions of 18 C-FA and lower proportions of 16:1 and LC-PUFA compared to fish from northern pristine reaches of the basin. Mid-Paraná showed intermediate values reflecting mixing of the North stock with migrating Buenos Aires P. lineatus identified by their lipid and contaminant profile. According to multivariate analyses, this geographical variation of fatty acid composition was strongly influenced by PCB concentration. Prochilodus lineatus assimilates the energy subsidy of sewage inputs through enhanced lipogenesis with dominant 18 C-FA and significant amounts of valuable LC-PUFA. This lipid alteration facilitates the bioaccumulation of PCBs which in turn may reinforce the adipogenic effect of sewage feeding.

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.

Molecular and morphometric characterization of two dental morphs of Saccodon dariensis (Parodontidae)

This study reports for the first time the roles of genetic and body phenotypic variation in two Saccodon dariensis dental morphs. Results showed a lack of ancient mitochondrial differentiation between morphs and body variations concordant with genetic polymorphism or differential plastic responses to diet quality and foraging strategies of S. dariensis.

Tometes kranponhah and Tometes ancylorhynchus (Characiformes: Serrasalmidae), two new phytophagous serrasalmids, and the first Tometes species described from the Brazilian Shield

Two new species of Tometes from the Brazilian Shield rapids are described. Tometes kranponhah is endemic to the Xingu River basin, whereas Tometes ancylorhynchus occurs both in the Xingu and the Tocantins-Araguaia River basins. The two species are sympatric in the Xingu drainages and have many similarities in morphology and colouration. Major diagnostic differences are the dark pigmentation on the opercle of T. kranponhah and its distinct snout shape and arrangement of premaxillary teeth. In addition, T. kranponhah is a large fish that is abundant in the Xingu River, whereas T. ancylorhynchus is a medium-sized fish for which there are few records.

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.