Water-breathing Fish Research Articles

Free fatty acid metabolism in the air-breathing African catfish ( Clarias gariepinus) during asphyxia

In several waterbreathing fish species, hypoxia induces a decrease in plasma free fatty acid (FFA) levels as opposed to an increase in air-breathing mammals. We hypothesised that this change is coupled to the mode of breathing. Therefore, we followed the metabolic response of cannulated air-breathing African catfish to an 8-h asphyxia period. The hematocrit and hemoglobin increased significantly upon asphyxia. However, no change was observed in the mean cellular hemoglobin concentration, indicating that more erythrocytes were brought into circulation. A continuous increase in plasma lactate concentration during asphyxia showed permanent activation of anaerobic glycolysis, pointing to a persistent oxygen shortage. Plasma glucose levels did not change, but FFA levels decreased significantly upon asphyxia with a concomitant increase in plasma noradrenaline levels. Thus, these results suggest that in the air-breathing African catfish noradrenaline mediated a decrease in plasma FFA levels similar to that in waterbreathing fish species.

Phylogeny of central CO2/pH chemoreception in vertebrates

The traditional view has been that respiratory chemoreceptors responsive to changes in PCO2/pH first evolved in air-breathing vertebrates at both peripheral and central sites. Levels of arterial PCO2 in water breathing fish are typically less than 2–3 torr and it has been assumed that the ventilatory responses of fish to changes in aquatic PCO2/pH were due to the effects of acidosis on haemoglobin oxygen transport. There is growing evidence, however, to suggest that fish also possess peripheral chemoreceptors responsive to changes in PCO2/pH per se that reside primarily in the gills, are innervated by the glassopharyngeal and vagus nerves, and respond primarily to changes in aquatic rather than arterial PCO2. Their distribution overlaps extensively with that of the gill O2 chemoreceptors in fish and it is not yet clear whether both responses arise from the same sensory cells. To date, there is no convincing evidence that strictly water breathing fish possess central chemoreceptors. There is, however, growing evidence to suggest that some species of air-breathing fish possess central CO2 chemoreceptors. Central chemosensitivity has been reported in in vitro brainstem-spinal cord preparations from both a primitive (holostean) and a modern (teleost) actinopterygian (ray finned) fish. Stimulation of these putative receptors had no effect on fictive gill ventilation but stimulated fictive air breathing. Unfortunately, the fictive breathing rates of these preparations were more than 25 times the resting rates reported for intact animals raising questions about the physiological significance of changes in the fictive motor output identified as air breathing under these conditions. In the South American lung-fish (a sarcopterygian fish belonging to the lineage giving rise to higher vertebrates), on the other hand, central perfusion with mock csf of differing pH stimulated air breathing at rates similar to those seen in control animals. While these data suggest that central chemoreceptors have arisen several times in evolutionary history, hand in hand with the evolution of air breathing, this issue is not yet totally resolved. An intriguing and related finding is that central CO2 chemosensitivity appears to develop slowly in amphibian tadpoles. It is not present in young tadpoles but develops over time. The receptors initially stimulate gill ventilation but transfer their influence to lung ventilation just prior to metamorphosis from the aquatic larval stage into the air breathing adult form. In association with this the primary location of the receptors in the brainstem shifts from a diffuse distribution to a rostral concentration. While central chemoreceptors have been demonstrated in reptiles and birds, not much is known of their properties or distribution. They have been well studied in mammals where there is growing evidence for multiple sites of central CO2/pH chemoreception and evidence to suggest that the mechanism of sensory transduction may vary both within and between receptor populations. While there has been much recent interest in the membrane channels, receptors and electrical coupling of several chemosensitive sites, this work has largely been on cells with downstream respiratory rhythmicity in preparations whose responses are very different (in terms of changes in frequency and amplitude of phrenic output) from that which is seen in intact animals. The phylogenetic trends that are emerging indicate that the use of CO2 chemoreception for cardio-respiratory processes may have arisen much earlier than previously believed, that CO2/pH chemoreception arose in the periphery before the evolution of central CO2/pH chemoreceptors, that the sites of CO2/pH chemoreception (both peripheral and central) have increased throughout the course of vertebrate evolution and that the mechanism of CO2/pH chemotransduction may vary. The sum of the data suggests that CO2/pH chemoreceptors have arisen multiple times, at multiple sites during vertebrate evolution.

Central control of the cardiovascular and respiratory systems and their interactions in vertebrates.

This review explores the fundamental neuranatomical and functional bases for integration of the respiratory and cardiovascular systems in vertebrates and traces their evolution through the vertebrate groups, from primarily water-breathing fish and larval amphibians to facultative air-breathers such as lungfish and some adult amphibians and finally obligate air-breathers among the reptiles, birds, and mammals. A comparative account of respiratory rhythm generation leads to consideration of the changing roles in cardiorespiratory integration for central and peripheral chemoreceptors and mechanoreceptors and their central projections. We review evidence of a developing role in the control of cardiorespiratory interactions for the partial relocation from the dorsal motor nucleus of the vagus into the nucleus ambiguus of vagal preganglionic neurons, and in particular those innervating the heart, and for the existence of a functional topography of specific groups of sympathetic preganglionic neurons in the spinal cord. Finally, we consider the mechanisms generating temporal modulation of heart rate, vasomotor tone, and control of the airways in mammals; cardiorespiratory synchrony in fish; and integration of the cardiorespiratory system during intermittent breathing in amphibians, reptiles, and diving birds. Concluding comments suggest areas for further productive research.

Ventilation and acid-base recovery following exhausting activity in an air-breathing fish

The effects of exhausting activity in normoxic (PO2=20.7 kPa) and hypoxic (PO2<2.7 kPa) water on ventilatory, metabolic and acid-base variables were examined in spotted gar (Lepisosteus oculatus) to determine the role of the air-breathing organ in supporting active metabolism and recovery. The level of aquatic hypoxia used effectively eliminated the gills as a site of O2 uptake, forcing the fish to respire as a unimodal air-breather. Swimming duration (until exhaustion) was not significantly different in normoxic and hypoxic water. Blood gas, acid-base, cardiovascular and ventilatory variables were monitored at intervals from 15 min to 24 h post-exercise. Fish survived exhaustive exercise using a combination of anaerobic metabolism and increased ventilation (aerial and aquatic), despite respiratory and metabolic acidoses. The cardiovascular effects of exercise (heart rate and dorsal aortic blood pressure) were minor. The metabolic effects of exercise were similar to those in unimodal water-breathing fish; however, even hypoxic animals recovered from exhaustive exercise by 24 h. Thus, the results of this study show that air breathing in L. oculatus allows gar to exercise to the same extent in normoxic and hypoxic water and enables them to re-establish blood gas and acid-base balance after exhaustive activity even in hypoxic water. <P>

Cardioventilatory responses to hypoxia and NaCN in the neotenous axolotl

Ventilatory and cardiac responses to hypoxia, sodium cyanide (NaCN), and intra-arterial injection of atropine, noradrenaline and DL-propranolol were investigated in the neotenous axolotl ( Ambystoma mexicanum). Hypoxia elicited increased gill and lung ventilation and a tachycardia. Gill ventilation and air-breathing were stimulated by NaCN infused either into the ventilatory water stream or into the bloodstream. Cardiac responses to NaCN were complex, with an initial bradycardia followed by a tachycardia. In all animals, the tachycardia developed subsequent to lung ventilation. Atropine raised resting heart rate and abolished the bradycardia elicited by NaCN. Noradrenaline stimulated gill ventilation and heart rate but not air-breathing. These responses were not abolished by DL-propranolol, and propranolol had no effect on responses to NaCN. The results indicate that the axolotl possesses O 2 chemo-sensitivity to both external and internal milieu, shows similar O 2 chemo-reflexes to those of larval anurans and air-breathing fish, but does not exhibit the β-adrenergic effects on ventilation observed in water-breathing fish.

Comparative lactic acidosis in fishes following pesticide stress

Lactic acid levels were estimated in blood, liver, muscle and heart-tissues of a water-breathing fish, Sarotherodon mossambicus and of an air-breathing fish, Channa striatus under control and 3 ppm sevin-exposed (for 24 h, 48 h, 72 h and 96 h) conditions. Based on the results obtained, the following points were concluded: (1) The water-breathing fish, S. mossambicus appeared to suffer severe lactic acidosis to a greater extent than that of the air-breathing fish, C. striatus during early periods (24 h) of sevin exposure. (2) Following prolonged exposure for 48 h and 72 h, S. mossambicus exhibited adaptive withdrawal of lactic acid from blood and muscle possibly into liver favouring the synthesis of glycogen (glycogenesis through Cori cycle) from lactic acid under sevin toxicity. (3) The reduction in lactic acid level in blood, liver and muscle of the air-breathing fish, C. striatus, under sevin exposure for 24 h and 48 h was suggestive of a possible oxidation of lactic acid (by rechannelling lactic acid into Krebs cycle via pyruvic acid) to meet the energy demand under sevin toxicity. (4) The onset of mild lactic acidosis in blood, muscle and liver during 72 h of sevin exposure of C. striatus suggested a possible inhibition of enzyme battery in the conversion of lactic acid into pyruvic acid.

Vascular organization of the head and respiratory organs of the air-breathing catfish, Heteropneustes fossilis.

Light and scanning electron microscopy of vascular replicas from the facultative air-breathing fish Heteropneustes fossilis show modifications in the macrocirculation of the respiratory organs and systemic circulation, whereas, gill microcirculation is similar to that found in typical water-breathing fish. Three and sometimes four ventral aortae arise directly from the bulbus. The most ventral vessel supplies the first pair of arches. Dorsal to this another aorta supplies the second gill arches, and a third, dorsal to, and larger than the other two, supplies the third and fourth arches and the air sacs. Occasionally a small vessel that may be the remnant of a primitive aortic arch arises from the first ventral aorta and proceeds directly to the mandibular region without perfusing gill tissue. The air sac is perfused by a large-diameter extension of the afferent branchial artery of the fourth gill arch and its circulation is in parallel with the gill arches. Blood drains from the air sac into the fourth arch epibranchial artery. A number of arteries also provide direct communication between the efferent air sac artery and the dorsal aorta. All four gill arches are well developed and contain respiratory (lamellar) and nonrespiratory (interlamellar and nutrient) networks common to gills of water-breathing fish. Air sac lamellae are reduced in size. The outer 30% of the air sac lamellar sinusoids are organized into thoroughfare channels; the remaining vasculature, normally embedded in the air sac parenchyma, is discontinuous. A gill-type interlamellar vasculature is lacking in the air sac circulation. Despite the elaborate development of the ventral aortae, there is little other anatomical evidence to suggest that gill and air sac outflow are separated and that dorsal aortic oxygen tensions are maintained when the gills are in a hypoxic environment. Physiological adjustments to hypoxic water conditions probably include temporal regulation of gill and air sac perfusion to be effective, if indeed they are so.

Calcium Fluxes in the Teleost Fish Tilapia (Oreochromis) in Water and in Both Water and Air in the Marble Goby (Oxyeleotris) and the Mudskipper (Periophthalmodon)

Unidirectional and net extrarenal calcium fluxes in water and in air on wet filter paper were obtained in the mudskipper, Periophthalmodon schlosseri, an obligate air breather, and in the marble goby, Oxyeleotris marmorata, which is fundamentally a water-breathing fish but which can survive extended periods of time on wet filter paper (facultative air breather). For comparison purposes, values were also obtained in water only from tilapia, Oreochromis mossambicus. This fish, which is an obligate water breather and cannot survive long in air, showed rates of influx, efflux, and net flux that were more than double those shown by the two species of gobies in water. In turn, the marble goby had significantly higher rates of influx, efflux, and net flux in water than seen in the mudskipper, Periophthalmodon schlosseri. The difference in net flux between Oxyeleotris and Periophthalmodon was not apparent when the fish were maintained on wet filter paper. On wet filter paper, when branchial/water contact was abolished, both the marble goby and the mudskipper showed significant reductions in unidirectional influx, but the specific activity of the blood was the same as when in water. Normal net flux rates were maintained because efflux decreased to near zero. The results suggest that much of the necessity to maintain an influx of calcium in fish is directly attributable to the necessity to replace calcium lost during branchial irrigation. We conclude, therefore, that these two species can perform cutaneous calcium transport at least when their gills are not exposed to water.

The Effects of Hypercapnia on the Arterial Acid-Base Status in the Tegu Lizard, Tupinambis Nigropunctatus

ABSTRACT The effects of hypercapnia on the arterial acid-base status of the Tegu lizard, Tupinambis nigropunctatus (Spix), were studied at 25 °C. Arterial increased over the first 2 h of hypercapnia causing a fall in arterial plasma pH (pHa) of about 0·17 units with ≈4% CO2 and about 0·3 units with ≈7 % CO2. In both conditions, plasma pH increased slightly (≈ 0·02 units) between 2 and 72 h. Plasma [HCO3−] rose during the initial increase of (by approx. 5·5 mmol l−1 with ≈7 % CO2; approx. 1·9 mmol l−1 with ≈4% CO2) during the first 2h, and further increased by 4 mmol I-1 between 2 and 72 h of hypercapnia, while did not change. The increases of plasma [HCO3−] resulted in a recovery of pH, by 38 or 32 % (≈4 and ≈7 % CO2, respectively) relative to the fall of pHa that would occur at constant [HCO3−]. The limited and incomplete compensation of pHa during environmental hypercapnia is consistent with data for other air-breathing ectothermic vertebrates, and contrasts with the typical response of water-breathing fish, in which compensation is usually complete.

Oxygen Acquisition of the Reedfish, Erpetoichthys Calabaricus

ABSTRACT In normoxic water at 25 °C, the reedfish (Erpetoichthys calabacicus) can breathe in both air and water, although water is the primary source of oxygen. This pattern of oxygen partitioning is altered by a number of factors. Increases in metabolic costs (e.g. locomotor activity) and decreases in aquatic oxygen concentration are met by increases in aerial oxygen uptake. Reedfish acclimated to 33 °C have increased lung breathing compared with fish acclimated to 25°C. Also, activity stimulates lung breathing more at 33 °C than at 25 °C. Unexpectedly, weight-specific oxygen uptake rates of reedfish at these two temperatures were not significantly different. In-creased lung-breathing compensates for changes in locomotor activity, dissolved oxygen and temperature, allowing reedfish to meet their overall oxygen requirements. Exposure of reedfish to six different combinations of oxygen and carbon dioxide indicated that lung ventilation frequencies were more labile than gill ventilation frequencies. The maximum change in lung ventilation rates was 849% above controls whereas the largest change in gill ventilation frequency was 27%. Exposure of reedfish to hyperoxia significantly de-pressed both gill and lung ventilation. Hypercapnic gases stimulated gill ventilation at both low (0·5%) and high (5%) concentrations; however, lung ventilation was only stimulated at the higher carbon dioxide concentration. The observed depression of gill ventilation frequencies in reedfish exposed to combinations of hypercapnic and hypoxic gases indicates that the inhibitory effect of low oxygen on gill ventilation dominates the stimulatory effect of hypercapnia. Overall, these data suggest that oxygen exerts a stronger influence in the control of respiration than carbon dioxide in this air-and water-breathing fish. Reedfish survived out of water for 6 and 8 h at 25 °C without obvious ill effects. Oxygen consumption rates of these fish were significantly less than those of similar sized reedfish measured in water at either 25 or 33°C. The respiratory physiology of the reedfish frees it from aquatic oxygen constraints and allows it to tolerate at least short-term terrestrial exposures.

Acid-base status of fish at different temperatures.

In the water-breathing fishes, rising temperatures are accompanied by progressive reduction in pH, reductions in bicarbonate concentration, and slight rises in CO2 partial pressure. The pH-temperature slope of both intra- and extracellular compartments varies considerably, from -0.009 to -0.033/degrees C, with a rather consistent pattern of red muscle greater than white muscle greater than heart. Three different approaches to acid-base analysis, the imidazole-alphastat model, the strong-ion difference analysis, and the delta-bicarbonate approach, were applied to a set of data from the fresh-water channel catfish (Ictalurus punctatus). A principal difficulty encountered in using all three approaches was that assumptions were required regarding the chemical behavior of the intracellular buffers, but the delta-bicarbonate approach has the practical advantage of emphasizing parameters that can be measured directly. Closed-system models are not generally applicable to fish, and the interest for future work lies in deciphering the significance of tissue-to-tissue variations in pH regulation and in elucidating the mechanisms of the strong-ion transfers.

The effect of respiratory mode and oxygen concentration on the risk of aerial predation in fishes

Six bimodal and six water-breathing species of fish were exposed to predation by a green heron (Butorides striatus) in a laboratory experiment to examine the hypothesis that aerial predation selects against the evolution and use of air breathing. Tests were performed at 1.6 and 0.5 mg O2∙L−1 ([Formula: see text] and 9 Torr, respectively; 1 Torr = 133.322 Pa). Most water breathers avoided the surface at 1.6 mg∙L−1 but not at 0.5 mg∙L−1, where they performed aquatic surface respiration. Most bimodal species breathed air at both oxygen concentrations. The risk of capture increased with proximity to the surface. The prey species responded to the predator by increasing mean depth, decreasing the rate of air breathing or aquatic surface respiration, and avoiding the vicinity of the predator when surfacing. Despite these and other antipredator characteristics, all species were vulnerable to capture in the test situation. Overall, the survivorship of water-breathing fishes was significantly higher than that of bimodal species at 1.6 mg∙L−1 and similar to that of bimodal species at 0.5 mg∙L−1. Aerial predation pressure should favor water breathing over air breathing except at oxygen concentrations lower than 0.5 mg∙L−1.

Hydrogen shuttles in air versus water breathing fishes

1. 1. The malate-aspartate cycle was demonstrable in subcellular preparations of hearts from Arapaima, Lepidosiren, and Synbranchus (obligate air breathers), Hoplerythriunus (facultative air breather), and Osteoglossum and Hoplias (obligate water breathers). 2. 2. Although no respiratory evidence for significant α-glycerophosphate cycle participation could be shown in the air breathers, this cycle was demonstrable in hearts of water breathers. 3. 3. In agreement with the O 2 uptake studies, it was possible to reconstruct the malate-aspartate, but not the α-glycerophosphate cycle, in isolated mitochondria from air breathers, while both shuttles could be reconstructed with heart mitochondria in the case of water breathing fishes.

A comparative study of the oxygen equilibria of blood from 40 genera of Amazonian fishes

1. We have examined the oxygen-affinity of the fresh, whole blood from representatives of 40 genera of Amazonian fishes.2. When all the air-breathing fishes and all the water-breathing fishes were considered, no differentiation in oxygen affinity could be distinguished, although in two cases of closely related species, i.e.Osteoglossum, a water breather, vsArapaima, an air breather, andHoplias, a water breather, vsHoplerythrinus, an air breather; the air breathers have bloods with lower oxygen affinity than do the water breathers.3. Significant differences in the oxygen affinity were found when fishes were considered by habitat: the oxygen affinities were in general correlated with available environmental oxygen and relative oxygen demand of the fishes.

Some kinetic properties of skeletal muscle pyruvate kinase from air-breathing and water-breathing fish of the Amazon

The kinetic properties of pyruvate kinase from skeletal muscle were studied in two species of air-breathing fish, Hoplerythrinus unitaeniatus and Arapaima gigas, and two species of water-breathing fish, Hoplias malabaricus and Osteoglossum bicirrhosum. It was found that the enzymes from Hoplias and Hoplerythrinus showed hyperbolic saturation kinetics for all substrates, were activated slightly by fructose 1,6-diphosphate, and were inhibited by phosphocreatine and citrate. The enzyme from Hoplias was inhibited by alanine, whereas the enzyme from Hoplerythrinus was not. The enzymes from Arapaima and Osteoglossum showed hyperbolic saturation kinetics for adenosine diphosphate, but the saturation kinetics for phusphoenol-pyruvate were sigmoidal. These enzymes were strongly activated by fructose 1,6-diphosphate and strongly inhibited by alanine, the former completely reversing the inhibition by the latter. Phosphocreatine and citrate were also found to be inhibitors of these enzymes, but the inhibition by phosphocreatine was not reversed by additions of fructose 1,6-diphosphate. The enzymes from the water-breathing fish were more sensitive to inhibition by alanine than were those from the air-breathing fish, but in other respects the enzymes were very similar.

Lactate dehydrogenase isozymes from heart and white muscle of water-breathing and air-breathing fish from the Amazon

Lactate dehydrogenase (LDH, EC 1.1.1.27) isozymes were studied from the white muscle and hearts of four species of Amazon fish, Osteoglossum bicirrhosum, an obligate water breather, and the closely related air breather, Arapaima gigas; Hoplias malabaricus, an obligate water breather, and Hoplerythrinus unitaeniatus, a facultative air breather. The LDH pattern was similar in closely related species but could not be correlated with changes in respiratory habits. All the isozymes from both heart and white muscle showed low substrate inhibition by pyruvate. The LDH from Osteoglossum skeletal white muscle showed sigmoidal kinetics with respect to pyruvate, rendered hyperbolic by the addition of 20 mM phosphocreatine. The kinetic properties appear to facilitate a dual function for white muscle in the absence of red muscle in the myotome. Phosphocreatine inhibition of LDH was observed in all the tissues studied and is suggested to be a more general phenomenon than has been previously supposed.

Myocardial inotrophy of CO2 in water- and air-breathing vertebrates.

A negative-inotropic effect of CO2 on myocardial contractility presumably occurs because increasing H+ concentration competes with Ca2+ at cellular membranes and proteins. Since air-breathing vertebrates have higher blood and tissue CO2 concentration than water breathers the question was raised whether the cardiac cell has a modified sensitivity to CO2 correlated with the evolutionary transition of vertebrates from water breathers to air breathers. The water-breathing fish, Salmo gairdneri, and the air-breathing turtle, Pseudemys scripta, were selected as experimental animals, since their total CO2 concentration differs markedly (3.0 and 16.0 mmol.kg-1). Electrically paced isometric ventricular strips from both species were subjected to a stepwise increase in PCO2 from 25 to 114 Torr (pH0 7.80 to 7.0; HCO3- 30 mM). Trout were additionally exposed to the same pH0 changes at 5 mM HCO3- by a stepwise increase in PCO2 (4.5-12 Torr). At each increase in PCO2 the turtle heart showed a lesser negative inotropic effect than trout. The present findings offer direct evidence that the negative inotropic effect of CO2 on heart muscle is inversely proportional to the in vivo levels of tissue CO2 concentration. The results obtained are discussed in relation to phylogenetical and ecological aspects of acid-base balance.

The role of intracellular Ca2+ under hypercapnic acidosis of cardiac muscle: Comparative aspects

1. Under hypercapnic acidosis an initial decrease of myocardial contractile force is seen, but in some vertebrate species it is followed by a recovery. The resulting force level is higher in air-breathers, like a turtle (Pseudemys scripta), a snake (Vipera berus), and the laboratory rat, than in the waterbreathing fishes, trout and carp. The hearts of the leopard frog and grass frog are intermediate although the former tolerate hypercapnic acidosis better than the latter. 2. Cyanide does not affect the hypercapnic force development of the leopard frog, while it induces a recovery process in that of the grass frog. Since cyanide is known to release intracellularly bound Ca2+ this suggests that the recovery involves a changed Ca2+ distribution. 3. Incubation of cardiac strips fromVipera berus and trout in a Na+- and Ca2+-free Ringer causes an increase in resting tension. Under hypercapnic acidosis a decrease of this tension occurs which, however, for the strips from the viper is followed by recovery. The recovery process thus seems to be independent of extracellular Ca2+ or Na+. It also seems independent of the Ca2+ contained in the sarcoplasmatic reticulum, since the recovery of resting tension in the viper strips is unaffected by pretreatment with caffeine. 4. In viper myocardial strips, which develop high force under anoxia, the force loss by acidosis is increased and spontaneous recovery substantially depressed when hypercapnia is imposed after a 60 min pretreatment with agents unloading mitochondrial Ca2+-stores (anoxia and anoxia + oligomycin). 5. These findings favour the hypothesis that hypercapnic acidosis triggers the release of Ca2+ from intracellular stores, probably from mitochondria.