Phytobiotics blend as a dietary supplement for Nile tilapia health improvement.

Functional additives of natural origin included as dietary supplements have become an alternative to synthetic antibiotics to improve health and resistance to ecologically correct pathogenic diseases in fish farming. We tested whether incorporating a mixture of phytobiotics such as volatile oils of thyme, red thyme and pepper rosemary into the diet improves growth performance, oxidative stress, immune and hematological responses and resistance of juvenile Nile tilapia when subjected to a challenge with Aeromonas hydrophila compared to a synthetic antibiotic (enrofloxacin). The experimental design was completely randomized with three experimental groups: control diet, diets containing a mixture of thyme phytobiotic essential oils, red thyme and pepper rosemary (FTB) and the synthetic antibiotic enrofloxacin (ATB), with four replicates (14 fish per repetition/experimental unit). Plasma glucose levels, leukocyte respiratory activity, serum lysozyme levels, number of circulating erythrocytes and leukocytes, levels of lipid peroxidation (LPO), catalase (CAT) and glutathione S-transferase (GST) activity at the end of 20 days of feeding (phase) were evaluated and 24 h after exposure to bacteria (phase II). The supplementation of FTB and ATB did not change the performance parameters, but it was sufficient to increase lysozyme, leukocytes, neutrophils and monocytes after the bacterial challenge, reduction of CAT and LPO activity and the highest GST activity (P < 0.05). The results of the present study suggest that FTB as a dietary supplement has benefits and can replace synthetic ATB, including supplementation with FTB for 20 days to provide greater antioxidant protection in Nile tilapia, mitigate the impacts of stressors and modulate immunity, providing to fish greater resistance and protection against diseases.

Cardiac contractility of the African sharptooth catfish, Clarias gariepinus: role of extracellular Ca2+, sarcoplasmic reticulum, and ß-adrenergic stimulation.

This study investigated the dependence of contraction from extracellular Ca2+, the presence of a functional sarcoplasmic reticulum (SR), and the effects of ß-adrenergic stimulation using isometric cardiac muscle preparations. Moreover, the expression of Ca2+-handling proteins such as SR-Ca2+-ATPase (SERCA), phospholamban (PLN), and Na+/Ca2+ exchanger (NCX) were also evaluated in the ventricular tissue of adult African sharptooth catfish, Clarias gariepinus, a facultative air-breathing fish. In summary, we observed that (1) contractility was strongly regulated by extracellular Ca2+; (2) inhibition of SR Ca2+-release by application of ryanodine reduced steady-state force production; (3) ventricular myocardium exhibited clear post-rest decay, even in the presence of ryanodine, indicating a decrease in SR Ca2+ content and NCX as the main pathway for Ca2+ extrusion; (4) a positive force-frequency relationship was observed above 60 bpm (1.0 Hz); (5) ventricular tissue was responsive to ß-adrenergic stimulation, which caused significant increases in twitch force, kept a linear force-frequency relationship from 12 to 96 bpm (0.2 to Hz), and improved the cardiac pumping capacity (CPC); and (6) African catfish myocardium exhibited similar expression patterns of NCX, SERCA, and PLN, corroborating our findings that both mechanisms for Ca2+ transport across the SR and sarcolemma contribute to Ca2+ activator. In conclusion, this fish species displays great physiological plasticity of E-C coupling, able to improve the ability to maintain cardiac performance under physiological conditions to ecological and/or adverse environmental conditions, such as hypoxic air-breathing activity.

Using aerobic exercise to evaluate sub-lethal tolerance of acute warming in fishes.

We investigated whether fatigue from sustained aerobic swimming provides a sub-lethal endpoint to define tolerance of acute warming in fishes, as an alternative to loss of equilibrium (LOE) during a critical thermal maximum (CTmax) protocol. Two species were studied, Nile tilapia (Oreochromis niloticus) and pacu (Piaractus mesopotamicus). Each fish underwent an incremental swim test to determine gait transition speed (UGT), where it first engaged the unsteady anaerobic swimming mode that preceded fatigue. After suitable recovery, each fish was exercised at 85% of their own UGT and warmed 1°C every 30 min, to identify the temperature at which they fatigued, denoted as CTswim Fish were also submitted to a standard CTmax, warming at the same rate as CTswim, under static conditions until LOE. All individuals fatigued in CTswim, at a mean temperature approximately 2°C lower than their CTmax Therefore, if exposed to acute warming in the wild, the ability to perform aerobic metabolic work would be constrained at temperatures significantly below those that directly threatened survival. The collapse in performance at CTswim was preceded by a gait transition qualitatively indistinguishable from that during the incremental swim test. This suggests that fatigue in CTswim was linked to an inability to meet the tissue oxygen demands of exercise plus warming. This is consistent with the oxygen and capacity limited thermal tolerance (OCLTT) hypothesis, regarding the mechanism underlying tolerance of warming in fishes. Overall, fatigue at CTswim provides an ecologically relevant sub-lethal threshold that is more sensitive to extreme events than LOE at CTmax.

Effects of Artemisia annua alcohol extract on physiological and innate immunity of Nile tilapia (Oreochromis niloticus) to improve health status.

Plants are a potential source of active molecules and are environmentally safer and cheaper than synthetic antibiotics. Bioactive compounds of Artemisia annua have shown pharmacological activities and are used globally as a supplement. The present study tested whether dietary supplementation with alcohol extract of the plant A. annua (ae-Aa; patent BR10201902707) improves the health status of juvenile Nile tilapia and increases resistance to diseases when fish are challenged with the bacteria Aeromonas hydrophila. The experimental design was completely randomized with four experimental groups (0.0, 0.1, 0.25, and 0.5% ae-Aa in the diets) with five repetitions (12 fish per repetition/experimental unit). We assessed serum glucose and cortisol levels in plasma, leukocyte respiratory activity, total plasma protein, serum lysozyme levels, as well as the number of circulating red blood cells and fish leukocytes at the end of the 30 days of feeding (phase I) and 24h after exposure to bacteria (phase II). The levels of lipid peroxidation, catalase activity and glutathione S-transferase of fish were also analyzed. The supplementation of 0.5% of ae-Aa was sufficient to increase the respiratory burst of leukocyte and lysozyme activity, total plasma protein, blood thrombocytes, neutrophils and monocytes after bacterial challenge (P < 0.05), and minimized stress response with decreases in plasmatic glucose and cortisol, and reduction in lipid peroxidation levels (P < 0.05). Results of the present study suggest that ae-Aa as a dietary supplement has benefits, including supplementation with 0.5% A. annua extract for 30 days to minimize the stress response and modulate innate immunity in Nile tilapia, providing fish with greater resistance and disease protection.

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 (V̇G) in the Mcys group at all O2 tensions except 140 and 120 mmHg, and a higher tidal volume (VT) 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 exercise training on excitation-contraction coupling, calcium dynamics and protein expression in the heart of the Neotropical fish Brycon amazonicus.

Matrinxã (Brycon amazonicus) is a great swimming performance teleost fish from the Amazon basin. However, the possible cardiac adaptations of this ability are still unknown. Therefore, the aim of the present work was to investigate the effects of prolonged exercise (EX group - 60days under 0.4BL·s-1) on ventricular contractility by (i) in-vitro analysis of contractility comparing the relative roles of sodium/calcium exchanger (NCX) and sarcoplasmic reticulum (SR) in the excitation-contraction (E-C) coupling and (ii) molecular analysis of NCX, sarcoplasmic reticulum Ca2+ ATPase (SERCA2) and phospholamban (PLB) expression and quantification. The exercise training significantly improved twitch tension, cardiac pumping capacity and the contraction rate when compared to controls (CT). Inhibition of the NCX function, replacing Na+ by Li+ in the physiological solutions, diminished cardiac contractility in the EX group, reduced all analyzed parameters under both high and low stimulation frequencies. The SR blockage, using 10µM ryanodine, caused ~50% tension reduction in CT at most analyzed frequencies while in EX, reductions (34-54%) were only found at higher frequencies. SR inhibition also decreased contraction and relaxation rates in both groups. Additionally, higher post-rest contraction values were recorded for EX, indicating an increase in SR Ca2+ loading. Higher NCX and PLB expression rates and lower SERCA2 rates were found in EX. Our data indicate that matrinxã presents a modulation in E-C coupling after exercise-training, enhancing the SR function under higher frequencies. This was the first study to functionally analyze the effects of swimming-induced exercise on fish cardiac E-C coupling.

Gill denervation eliminates the barostatic reflex in a neotropical teleost, the tambaqui (Colossoma macropomum).

The baroreflex is one of the most important regulators of cardiovascular homeostasis in vertebrates. It begins with the monitoring of arterial pressure by baroreceptors, which constantly provide the central nervous system with afferent information about the status of this variable. Any change in arterial pressure relative to its normal state triggers autonomic responses, which are characterized by an inversely proportional change in heart rate and systemic vascular resistance and which tend to restore pressure normality. Although the baroreceptors have been located in mammals and other terrestrial vertebrates, their location in fish is still not completely clear and remains quite controversial. Thus, the objective of this study was to locate the baroreceptors in a teleost, the Colossoma macropomum. To do so, the occurrence and efficiency of the baroreflex were both analyzed when this mechanism was induced by pressure imbalancements in intact fish (IN), first-gill-denervated fish (G1), and total-gill-denervated fish (G4). The pressure imbalances were initiated through the administration of the α1-adrenergic agonist phenylephrine (100 µg kg(-1)) and the α1-adrenergic antagonist prazosin (1 mg kg(-1)). The baroreflex responses were then analyzed using an electrocardiogram that allowed for the measurement of the heart rate, the relationship between pre- and post-pharmacological manipulation heart rates, the time required for maximum chronotropic baroreflex response, and total heart rate variability. The results revealed that the barostatic reflex was attenuated in the G1 group and nonexistent in G4 group, findings which indicate that baroreceptors are exclusively located in the gill arches of C. macropomum.

Activation of the cannabinoid type 2 (CB2) receptor improves cardiac contractile performance in fish, Brycon amazonicus.

In addition to their well-known classical effects, cannabinoid CB1 and CB2 receptors have also been involvement in both deleterious and protective actions on the heart under various pathological conditions. While the potential therapeutic applications of the endocannabinoid system in the context of cardiovascular function are indeed a viable prospect, significant debate exists within the literature regarding whether CB1, CB2, or a combination of both receptors exert a favorable influence on cardiac function. Hence, the aim of this study was to investigate the effects of CB1 + CB2 or CB2 agonists on cardiac excitation-contraction (E-C) coupling, utilizing fish (Brycon amazonicus) as an experimental model. The CB2 agonist elicited marked positive inotropic and lusitropic responses in isolated ventricular myocardium, induced cyclic adenosine 3',5'-monophosphate (cAMP) production, and upregulated critical Ca2+ handling proteins, such as sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) and Na+/Ca2+ exchanger (NCX). Our current study demonstrated, for the first time, that CB2 receptor activation-induced effects improved the efficiency of Ca2+ cycling, excitation-contraction coupling (E-C coupling), and cardiac performance in under physiological conditions. Hence, CB2 receptors could be considered a potential therapeutic target for modulating cardiac contractile dysfunctions.

Dietary intake of inorganic mercury: bioaccumulation and oxidative stress parameters in the neotropical fish Hoplias malabaricus.

This study evaluated the effects of trophic and subchronic exposure to inorganic mercury (Hg) on the oxidative stress biomarkers and its bioaccumulation potential in the liver, gills, white muscle and heart of the freshwater top predator fish, Hoplias malabaricus, fed with contaminated live juveniles of matrinxã, Brycon amazonicus, as prey vehicle. Inorganic mercury increased superoxide dismutase, catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase, and glutathione reductase (GR) activities in the liver, white muscle and heart. Gills CAT activity remained unchanged while GPx and GR values showed a significant decrease. In the liver and gills, Hg induced significant increase in the reduced (GSH) and oxidized (GSSG) glutathione content, concomitantly with a significant decrease in [GSH]/[GSSG] ratio. Differently, in cardiac tissue, the Hg caused an increase in GSH level and increase in [GSH]/[GSSG] ratio. Lipid and protein oxidation and metallothionein levels were significantly higher after Hg trophic exposure in the liver, gills and heart, but remained at control values in the white muscle. Tissue-specific responses against oxidative stress were observed, and the liver and gills were the most sensitive organs, showing signs of redox homeostasis failure. At the end of the experiment, dietary inorganic mercury accumulated through food chain levels. In order, Hg bioaccumulation was: gills > liver >> white muscle = heart. These results pointed out the potential of inorganic Hg to bioaccumulate in aquatic systems. Taken together, our findings suggest that Hg, even in the inorganic form and sublethal amounts, is a risk factor for aquatic biota.

Copper sulfate affects Nile tilapia (Oreochromis niloticus) cardiomyocytes structure and contractile function.

Copper sulfate (CuSO(4))is an inorganic chemical product worldwide used as an algaecide and a fungicide in aquaculture and agriculture and being discharged into freshwater environments where it can affect the freshwater fauna, especially fishes. The impact of copper on fish cardiac function was analyzed in two groups of Nile tilapias, Oreochromis niloticus (control group and group exposed to 1 mg l(-1) of CuSO(4) for 96 h). Structural and ultra-structural changes were studied and related to perturbations of the inotropic and chronotropic responses of ventricle strips. Fish of Cu exposed group did not show significant alterations in the medium diameter and in the percentage of collagen in the cardiac myocytes when evaluated through the light microscope. However, the ultrastructural analysis revealed cellular swelling followed by mitochondrial swelling. The myofibrils did not show significant variations among groups. Force contraction was significantly decreased, and rates of time to tension increase (contraction) and decrease (relaxation) were significantly augmented after copper exposure. The results suggest that the copper sulfate impairs the oxidative mitochondrial function and consequently alters the cardiac performance of this species.

Hormetic-like dose-response induced by alternagin-C, a protein isolated from urutu snake (Rhinocerophis alternatus) venom, in fish (Hoplias malabaricus) cardiac contractility.

The aim of this study was to evaluate the effects of different doses of alternagin-C, a disintegrin-like protein from Rhinocerophis alternatus venom, on myocardial contractility of the freshwater fish Hoplias malabaricus, an alternative model to contractile function studies. Alternagin-C treatment exhibited a hormetic-like dose-response curve with a strong positive inotropism and enhanced cardiac pumping capacity at low dose, whereas a modest inotropism and a left shift in the force-frequency relationship was registered at high dose.

Postprandial cardiorespiratory responses and the regulation of digestion-associated tachycardia in Nile tilapia (Oreochromis niloticus).

Cardiorespiratory adjustments that occur after feeding are essential to supply the demands of digestion in vertebrates. The well-documented postprandial tachycardia is triggered by an increase in adrenergic activity and by non-adrenergic non-cholinergic (NANC) factors in mammals and crocodilians, while it is linked to a withdrawal of vagal drive and NANC factors in non-crocodilian ectotherms-except for fish, in which the sole investigation available indicated no participation of NANC factors. On the other hand, postprandial ventilatory adjustments vary widely among air-breathing vertebrates, with different species exhibiting hyperventilation, hypoventilation, or even no changes at all. Regarding fish, which live in an environment with low oxygen capacitance that requires great ventilatory effort for oxygen uptake, data on the ventilatory consequences of feeding are also scarce. Thus, the present study sought to investigate the postprandial cardiorespiratory adjustments and the mediation of digestion-associated tachycardia in the unimodal water-breathing teleost Oreochromis niloticus. Heart rate (fH), cardiac autonomic tones, ventilation rate (fV), ventilation amplitude, total ventilation and fH/fV variability were assessed both in fasting and digesting animals under untreated condition, as well as after muscarinic cholinergic blockade with atropine and double autonomic blockade with atropine and propranolol. The results revealed that digestion was associated with marked tachycardia in O. niloticus, determined by a reduction in cardiac parasympathetic activity and by circulating NANC factors-the first time such positive chronotropes were detected in digesting fish. Unexpectedly, postprandial ventilatory alterations were not observed, although digestion triggered mechanisms that were presumed to increase oxygen uptake, such as cardiorespiratory synchrony.

Hypercarbic cardiorespiratory reflexes in the facultative air-breathing fish jeju (Hoplerythrinus unitaeniatus): the role of branchial CO2 chemoreceptors.

The aim of the present study was to determine the roles that externally versus internally oriented CO(2)/H(+)-sensitive chemoreceptors might play in promoting cardiorespiratory responses to environmental hypercarbia in the air-breathing fish, Hoplerythrinus unitaeniatus (jeju). Fish were exposed to graded hypercarbia (1, 2.5, 5, 10 and 20% CO(2)) and also to graded levels of environmental acidosis (pH approximately 7.0, 6.0, 5.8, 5.6, 5.3 and 4.7) equal to the pH levels of the hypercarbic water to distinguish the relative roles of CO(2) versus H(+). We also injected boluses of CO(2)-equilibrated solutions (5, 10 and 20% CO(2)) and acid solutions equilibrated to the same pH as the CO(2) boluses into the caudal vein (internal) and buccal cavity (external) to distinguish between internal and external stimuli. The putative location of the chemoreceptors was determined by bilateral denervation of branches of cranial nerves IX (glossopharyngeal) and X (vagus) to the gills. The data indicate that the chemoreceptors eliciting bradycardia, hypertension and gill ventilatory responses (increased frequency and amplitude) to hypercarbia are exclusively branchial, externally oriented and respond specifically to changes in CO(2) and not H(+). Those involved in producing the cardiovascular responses appeared to be distributed across all gill arches while those involved in the gill ventilatory responses were located primarily on the first gill arch. Higher levels of aquatic CO(2) depressed gill ventilation and stimulated air breathing. The chemoreceptors involved in producing air breathing in response to hypercarbia also appeared to be branchial, distributed across all gill arches and responded specifically to changes in aquatic CO(2). This would suggest that chemoreceptor groups with different orientations (blood versus water) are involved in eliciting air-breathing responses to hypercarbia in jeju.

Inorganic mercury exposure: toxicological effects, oxidative stress biomarkers and bioaccumulation in the tropical freshwater fish matrinxã, Brycon amazonicus (Spix and Agassiz, 1829).

Alterations in the antioxidant cellular system have often been proposed as biomarkers of pollutant-mediated toxicity. This study evaluated the effects of mercury on oxidative stress biomarkers and bioaccumulation in the liver, gills, white muscle and heart of the freshwater fish matrinxã, Brycon amazonicus, exposed to a nominal and sub-lethal concentration (~20% of 96 h-LC(50)) of 0.15 mg L(-1) of mercury chloride (HgCl(2)) for 96 h in a static system. Increases in superoxide dismutase, catalase, glutathione peroxidase (GPx), glutathione S-transferase (GST) and glutathione reductase (GR) were observed in all tissues after HgCl(2) exposure, except for white muscle GR activity and hepatic GPx. In the liver and gills, the exposure to HgCl(2) also induced significant increases in reduced glutathione (GSH). Conversely, exposure to HgCl(2) caused a significant decrease in the GSH levels and an increase in the oxidized glutathione (GSSG) content in the white muscle, while both GSH and GSSG levels increased significantly in the heart muscle. Metallothionein concentrations were significantly high after HgCl(2) exposure in the liver, gills and heart, but remained at control values in the white muscle. HgCl(2) exposure induced oxidative damage, increasing the lipid peroxidation and protein carbonyl content in all tissues. Mercury accumulated significantly in all the fish tissue. The pattern of accumulation follows the order gills > liver >> heart > white muscle. In conclusion, these data suggest that oxidative stress in response to inorganic mercury exposure could be the main pathway of toxicity induced by this metal in fish.

The combined effect of copper and low pH on antioxidant defenses and biochemical parameters in neotropical fish pacu, Piaractus mesopotamicus (Holmberg, 1887).

Copper sulfate is widely used in aquaculture. Exposure to this compound can be harmful to fish, resulting in oxidative metabolism alterations and gill tissue damage. Pacu, Piaractus mesopotamicus, (wt = 43.4 +/- 3.35 g) were distributed in experimental tanks (n = 10; 180 l) and exposed for 48 h to control (without copper addition), 0.4Cu (0.4 mg l(-1)), 0CupH (without copper addition, pH = 5.0) and 0.4CupH (0.4 mg l(-1), pH = 5.0). In liver and red muscle, the superoxide dismutase (SOD) was responsive to the increases in the aquatic copper. The plasmatic intermediary metabolites and hematological variables in the fish of group 0.4Cu were similar to those of the control group. Conversely, the exposure to 0.4CupH caused an increase in the plasmatic lactate, number of red blood cells (RBC) and hemoglobin (Hb). Plasmatic copper concentration [Cu(p)] increased in group 0.4Cu and 0.4CupH, which is higher in group 0.4CupH, suggests an effect of water pH on the absorbed copper. Exposure to 0.4Cu and 0.4CupH resulted in a reduction in the Na(+)/K(+)-ATPase activity and an increase in metallothionein (MT) in the gills. Exposure to 0CupH caused a decrease in glucose and pyruvate concentrations and an increase in RBC, Hb, and the branchial Na(+)/K(+)-ATPase activity. These responses suggest that the fish triggered mechanisms to revert the blood acidosis, save energy and increase the oxygen uptake. MT was an effective biomarker, responding to copper in different pHs and dissolved oxygen. Combined-factors caused more significant disturbance in the biomarkers than single-factors.

Cardio-respiratory function and oxidative stress biomarkers in Nile tilapia exposed to the organophosphate insecticide trichlorfon (NEGUVON).

The cardio-respiratory function, oxidative stress and fish antioxidants were analyzed in juvenile Nile tilapia exposed for 96 h to a sublethal trichlorfon (TRC-Neguvon, Bayer) concentration of 0.5 mg L(-1). The exposure to TRC induced oxidative stress in the heart, as manifested by the glutathione S-transferase depletion and hydroperoxide elevation, and was the most sensitive organ when compared to the liver and gills, in which the antioxidant mechanisms against TRC exposure were sufficient to remove reactive oxygen species (ROS), preventing the increase of lipid peroxidation. TRC exposure also reduced O(2) uptake (V O(2)) and increased the critical oxygen tension (PcO(2)), reducing the species capacity to survive prolonged hypoxic conditions. The heart rate and force contraction were significantly impaired, making the heart the most sensitive organ when exposed to the TRC.

Control of air-breathing in fishes: Central and peripheral receptors.

This review considers the environmental and systemic factors that can stimulate air-breathing responses in fishes with bimodal respiration, and how these may be controlled by peripheral and central chemoreceptors. The systemic factors that stimulate air-breathing in fishes are usually related to conditions that increase the O2 demand of these animals (e.g. physical exercise, digestion and increased temperature), while the environmental factors are usually related to conditions that impair their capacity to meet this demand (e.g. aquatic/aerial hypoxia, aquatic/aerial hypercarbia, reduced aquatic hidrogenionic potential and environmental pollution). It is now well-established that peripheral chemoreceptors, innervated by cranial nerves, drive increased air-breathing in response to environmental hypoxia and/or hypercarbia. These receptors are, in general, sensitive to O2 and/or CO2/H+ levels in the blood and/or the environment. Increased air-breathing in response to elevated O2 demand may also be driven by the peripheral chemoreceptors that monitor O2 levels in the blood. Very little is known about central chemoreception in air-breathing fishes, the data suggest that central chemosensitivity to CO2/H+ is more prominent in sarcopterygians than in actinopterygians. A great deal remains to be understood about control of air-breathing in fishes, in particular to what extent control systems may show commonalities (or not) among species or groups that have evolved air-breathing independently, and how information from the multiple peripheral (and possibly central) chemoreceptors is integrated to control the balance of aerial and aquatic respiration in these animals.

The autonomic control of upright posture tachycardia in the arboreal lizard Iguana iguana.

In terrestrial environments, upright spatial orientation can dramatically influence animals' hemodynamics. Generally, large and elongated species are particularly sensitive to such influence due to the greater extent of their vascular beds being verticalized, favoring the establishment of blood columns in their bodies along with caudal blood pooling, and thus jeopardizing blood circulation through a cascade effect of reductions in venous return, cardiac filling, stroke volume, cardiac output, and arterial blood pressure. This hypotension triggers an orthostatic-(baroreflex)-tachycardia to normalize arterial pressure, and despite the extensive observation of this heart rate (fH ) adjustment in experiments on orthostasis, little is known about its mediation and importance in ectothermic vertebrates. In addition, most of the knowledge on this subject comes from studies on snakes. Thus, our objective was to expand the knowledge on this issue by investigating it in an arboreal lizard (Iguana iguana). To do so, we analyzed fH , cardiac autonomic tones, and fH variability in horizontalized and tilted iguanas (0°, 30°. and 60°) before and after muscarinic blockade with atropine and double autonomic blockade with atropine and propranolol. The results revealed that I. Iguana exhibits significant orthostatic-tachycardia only at 60o inclinations-a condition that is primarily elicited by a withdrawal of vagal drive. Also, as in humans, increases in low-frequency fH oscillations and decreases in high-frequency fH oscillations were observed along with orthostatic-tachycardia, suggesting that the mediation of this fH adjustment may be evolutionarily conserved in vertebrates.

Microcystin-LR leads to oxidative damage and alterations in antioxidant defense system in liver and gills of Brycon amazonicus (SPIX & AGASSIZ, 1829).

Microcystin's (MCs) are toxins produced by several groups of cyanobacteria, in water bodies throughout the world, in a process which is being intensified by human action. Among the variants of MCs, MC-LR stands out for its distribution and toxicity. MCs are potent inhibitors of protein phosphatases 1 and 2 A, which causes disruption of the cytoskeleton and consequent cell death. They can also alter the antioxidant system and induce oxidative stress in various organs of many species. There is, however, a lack of information about the effects of MCs on the antioxidant system and oxidative damage in Brazilian fishes. This study evaluated the effect of microcystin-LR on the antioxidant system in liver and gills of the Brazilian fish Brycon amazonicus, after 48 h of i.p injection of 100 µg MC-LR.kg-1 body mass. The liver exhibited increases in the activity of GST (74%) and GPx (217%), and a 47% decrease in SOD activity, with no changes in CAT values. In the gills of fish exposed to MC-LR, CAT and GPx activities did not show significant changes, while SOD and GST activity decreased by 66% and 37%, respectively. The GSH content did not change significantly in the liver, however, a decrease of 43% was observed in the gills. Oxidative damage measured by protein oxidation (PC) and lipoperoxidation (LPO) showed significant effects in both tissues. In hepatic tissue, there was no change in PC levels but LPO increased by 116%. Conversely, in the gills LPO levels did not change but PC increased by 317%. In conclusion, these data show that MC-LR induces oxidative damage in both tissues but in different ways, with being liver most sensitive to LPO and gills to PC. This also suggests that the gills are most sensitive to oxidative stress than liver, due to the inhibition of its antioxidant responses following MC-LR exposure.

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.