Changes in the respiratory properties of the blood in the carp,Cyprinus carpio, induced by diurnal variation in ambient oxygen tension

Rapid and reversible modulation of blood haemoglobin content during diel cycles of hypoxia in killifish (Fundulus heteroclitus)

We investigated whether fish can make dynamic haematological adjustments to support aerobic metabolism during repeated cycles of hypoxia-reoxygenation. Killifish were acclimated to normoxia, constant hypoxia (2 kPa O₂), or intermittent cycles of nocturnal hypoxia (12 h of normoxia: 12 h of 2 kPa O₂ hypoxia) for 28 days. Normoxia-acclimated fish were sampled in the daytime in normoxia and after exposure to a single bout of nocturnal hypoxia. Each hypoxia acclimation group were sampled at the PO₂ experienced during acclimation during both the day and night. All acclimation groups had increased blood haemoglobin content and haematocrit and reduced spleen mass during nocturnal hypoxia compared to normoxic controls. Blood haemoglobin content was negatively correlated with spleen mass at both the individual and group level. Fish acclimated to intermittent hypoxia rapidly reversed these changes during diurnal reoxygenation. The concentrations of haemoglobin, ATP, and GTP within erythrocytes did not vary substantially between groups. We also measured resting O₂ consumption rate (MO₂) and maximum MO₂ (induced by an exhaustive chase) in hypoxia in each acclimation group. Fish acclimated to intermittent hypoxia maintained higher resting MO₂ than other groups in hypoxia, comparable to the resting MO₂ of normoxia-acclimated controls measured in normoxia. Differences in resting MO₂ in hypoxia did not result from variation in O₂ transport capacity, because maximal MO₂ in hypoxia always exceeded resting MO₂. Therefore, reversible modulation of blood haemoglobin content along with metabolic adjustments help killifish cope with intermittent cycles of hypoxia in the estuarine environment.

Hypoxia tolerance and metabolic coping strategies in Oreochromis niloticus

The Nile tilapia (Oreochromis niloticus) is widely farmed in tropical and subtropical pond culture. O. niloticus is recognized as a species that is tolerant of hypoxic conditions, a trait that may largely be responsible for the success of this species in aquaculture. Until now, neither coping mechanisms nor a comparison of various indices of hypoxia tolerance to characterize the response to hypoxia, have been described. In the present study, Nile tilapia were subjected to hypoxia of increasing severity and duration to examine effects on metabolic rate (MO₂) and post hypoxic oxygen debt. MO₂ was measured during periods of severe hypoxia at 2.1 kPa O₂ (10% oxygen saturation) lasting between 2 and 24 h at 27 °C. Hypoxia tolerance was assessed by determining the critical oxygen tension (P_crit) and the pO₂ at which loss of equilibrium (LOE) occurred. We show that the tolerance of Nile tilapia to severe hypoxia is largely achieved through a capacity for metabolic depression. Despite prolonged exposure to dissolved oxygen levels below P_crit, the fish showed little excess post-hypoxic oxygen consumption (EPHOC) upon return to normoxic conditions. LOE did not occur until conditions became near-anoxic. Blood pH was not affected by severe hypoxia (2.1 kPa O₂), but a significant acidosis occurred during LOE, accompanied by a significant elevation in lactate and glucose levels. The results from the present study indicate that Nile tilapia do not switch to anaerobic metabolism during hypoxia until pO₂ falls below 2.1 kPa.

Diel cycling hypoxia enhances hypoxia-tolerance in rainbow trout (Oncorhynchus mykiss): evidence of physiological and metabolic plasticity

Many fish naturally encounter a daily cycle of hypoxia but it is unclear whether this exposure hardens hypoxia-intolerant fish to future hypoxia or leads to accumulated stress and death. Rainbow trout (Oncorhynchus mykiss) is a putatively hypoxia-sensitive species found in rivers and estuaries that may routinely experience hypoxic events. Trout were exposed to 1 of 4 135h treatments in a swim-tunnel respirometer: 1) air-saturated control (20.7 kPa PO2); 2) diel cycling O2 (20.7-4.2 kPa over 24h); 3) acute hypoxia (130h at 20.7 kPa PO2 followed by 5h at 4.2 kPa PO2); 4) the mean oxygen tension (12.4 kPa PO2) experienced by the diel cycled fish. Some responses were similar in diel O2 cycled and mean PO2-treated fish but overall exposure to ecologically-representative diel hypoxia cycles improved hypoxia tolerance. Diel hypoxia-induced protective responses included increased inducible HSP70 concentration and mean corpuscular hemoglobin concentration, as well as reduced plasma cortisol. Acclimation to diel hypoxia allowed metabolic rates to decline during hypoxia, reduced oxygen debt following subsequent exposures, and allowed fish to return to an anabolic phenotype. The data demonstrate that acute diel cycling hypoxia improves hypoxia tolerance in previously intolerant fish through the activation of cellular protective mechanisms and a reduction in metabolic O2 requirements.

Distinct metabolic adjustments arise from acclimation to constant hypoxia and intermittent hypoxia in estuarine killifish (Fundulus heteroclitus)

Many fish experience daily cycles of hypoxia in the wild, but the physiological strategies for coping with intermittent hypoxia are poorly understood. We examined how killifish adjust O2 supply and demand during acute hypoxia, and how these responses are altered after prolonged acclimation to constant or intermittent patterns of hypoxia exposure. We acclimated killifish to normoxia (∼20 kPa O2), constant hypoxia (2 kPa) or intermittent cycles of nocturnal hypoxia (12 h:12 h normoxia:hypoxia) for 28 days, and then compared whole-animal O2 consumption rates (ṀO2) and tissue metabolites during exposure to 12 h of hypoxia followed by reoxygenation in normoxia. Normoxia-acclimated fish experienced a pronounced 27% drop in ṀO2 during acute hypoxia, and modestly increased ṀO2 upon reoxygenation. They strongly recruited anaerobic metabolism during acute hypoxia, indicated by lactate accumulation in plasma, muscle, liver, brain, heart and digestive tract, as well as a transient drop in intracellular pH, and they increased hypoxia inducible factor (HIF)-1α protein abundance in muscle. Glycogen, glucose and glucose-6-phosphate levels suggested that glycogen supported brain metabolism in hypoxia, while the muscle used circulating glucose. Acclimation to constant hypoxia caused a stable ∼50% decrease in ṀO2 that persisted after reoxygenation, with minimal recruitment of anaerobic metabolism, suggestive of metabolic depression. By contrast, fish acclimated to intermittent hypoxia maintained sufficient O2 transport to support normoxic ṀO2, modestly recruited lactate metabolism and increased ṀO2 dramatically upon reoxygenation. Both groups of hypoxia-acclimated fish had similar glycogen, ATP, intracellular pH and HIF-1α levels as normoxic controls. We conclude that different patterns of hypoxia exposure favour distinct strategies for matching O2 supply and O2 demand.

Dynamics of blood viscosity regulation during hypoxic challenges in the chicken embryo (Gallus gallus domesticus)

Hypoxia in chicken embryos increases hematocrit (Hct), blood O2 content, and blood viscosity. The latter may limit O2 transport capacity (OTC) via increased peripheral resistance. Hct increase may result from increased nucleated red blood cell concentration ([RBC]) and mean corpuscular volume (MCV) or reduced plasma volume. We hypothesized changes in Hct, hemoglobin concentration ([Hb]), [RBC] and MCV and their effects on viscosity would reduce OTC. Five experimental treatments that increase Hct were conducted on day 15 embryos: 60min water submergence with 60min recovery in air; exposure to 15% O2 with or without 5% CO2 for 24 h with 6 h recovery; or exposure to 10% O2 with or without 5% CO2 for 120 min with 120 min recovery. Control Hct, [Hb], [RBC], MCV, and viscosity were approximately 26%, 9g%, 2.0 10(6)μL(-1), 130μm(3), and 1.6mPas, respectively. All manipulations increased Hct and blood viscosity without changing blood osmolality (276mmolkg(-1)). Increased viscosity was attributed to increased [RBC] and MCV in submerged embryos, but solely MCV in embryos experiencing 10% O2 regardless of CO2. Blood viscosity in embryos exposed to 15% O2 increased via increased MCV alone, and viscosity was constant during recovery despite increased [RBC]. Consequently, blood viscosity was governed by MCV and [RBC] during submergence, while MCV was the strongest determinant of blood viscosity in extrinsic hypoxia with or without hypercapnia. Increased Hct and blood O2 content did not compensate for the effect of increased viscosity on OTC during these challenges.

Distinct physiological strategies are used to cope with constant hypoxia and intermittent hypoxia in killifish (Fundulus heteroclitus)

Many fish encounter hypoxia on a daily cycle, but the physiological effects of intermittent hypoxia are poorly understood. We investigated whether acclimation to constant (sustained) hypoxia or to intermittent diel cycles of nocturnal hypoxia (12 h normoxia:12 h hypoxia) had distinct effects on hypoxia tolerance or on several determinants of O2 transport and O2 utilization in estuarine killifish. Adult killifish were acclimated to normoxia, constant hypoxia, or intermittent hypoxia for 7 or 28 days in brackish water (4 ppt). Acclimation to both hypoxia patterns led to comparable reductions in critical O2 tension and resting O2 consumption rate, but only constant hypoxia reduced the O2 tension at loss of equilibrium. Constant (but not intermittent) hypoxia decreased filament length and the proportion of seawater-type mitochondrion-rich cells in the gills (which may reduce ion loss and the associated costs of active ion uptake), increased blood haemoglobin content, and reduced the abundance of oxidative fibres in the swimming muscle. In contrast, only intermittent hypoxia augmented the oxidative and gluconeogenic enzyme activities in the liver and increased the capillarity of glycolytic muscle, each of which should facilitate recovery between hypoxia bouts. Neither exposure pattern affected muscle myoglobin content or the activities of metabolic enzymes in the brain or heart, but intermittent hypoxia increased brain mass. We conclude that the pattern of hypoxia exposure has an important influence on the mechanisms of acclimation, and that the optimal strategies used to cope with intermittent hypoxia may be distinct from those for coping with constant hypoxia.

Hypoxia-induced oxidative DNA damage links with higher level biological effects including specific growth rate in common carp, Cyprinus carpio L

Both hypoxia and hyperoxia, albeit in different magnitude, are known stressors in the aquatic environment. Adopting an integrated approach, mirror carp (Cyprinus carpio L.), were exposed chronically (i.e. 30 days) to hypoxic (1.8 ± 1.1 mg O(2) l(-1)) and hyperoxic (12.3 ± 0.5 mg O(2) l(-1)) conditions and resultant biological responses or biomarkers were compared between these two treatments as well as with fish held under normoxic conditions (7.1 ± 1.04 mg O(2) l(-1)). The biomarkers determined included the activities of glutathione peroxidase (GPx), measurement of oxidative DNA damage (using modified Comet assay employing bacterial enzymes: Fpg and Endo-III), haematological parameters, histopathological and ultrastructural examination of liver and gills. Specific growth rate (SGR) of the fish, as an important ecotoxicological parameter was also determined over the exposure period. The study suggested that while the levels of hepatic GPx were unaffected, there was a significant difference in activity in the blood plasma under different exposure conditions; the hyperoxic group showed increased GPx activity by approximately 37% compared to normoxic group and the hypoxic group showed a decrease by approximately 38% than the normoxic group. Interestingly, oxidative DNA damage was significantly higher in both hypoxic and hyperoxic by approximately 25% compared to normoxic conditions, Fpg showing enhanced level of damage compared to the Endo-III treatment (P < 0.001). The haematological parameters showed enhanced values under hypoxic conditions. Transmission electron microscopic (TEM) studies revealed damage to liver and gill tissues for both the treatments. Interestingly, SGR of fish was significantly lowered in hypoxic by approx. 30% compared to normoxic condition and this was found to be correlated with DNA damage (R = -0.82; P = 0.02). Taken together, these results indicate that prolonged exposure to both hypoxic and hyperoxic conditions induce oxidative stress responses at both DNA and tissue levels, and hypoxia can result in compensatory changes in haematological and growth parameters which could influence Darwinian fitness of the biota with wider ecological implications.

Population variation in hypoxic responses of the cichlid Pseudocrenilabrus multicolor victoriae

F1 offspring of the African cichlid Pseudocrenilabrus multicolor victoriae Seegers, 1990 from swamp (low oxygen) and lake (high oxygen) origin were raised under normoxia and submitted to hypoxia acclimation (0.8 ± 0.4 mg·L–1) and normoxia acclimation (7.4 ± 0.3 mg·L–1) for 4 weeks. Haematocrit and lactate dehydrogenase (LDH) specific activities in the liver, white skeletal muscle, heart, and brain were measured. For haematocrit and LDH activities of liver, muscle, and heart, the response to acclimation depended upon population of origin. In general, fish from the swamp population showed a more “typical” hypoxic response (increased haematocrit and LDH activities), whereas fish from the lake population either did not respond or showed the opposite response. The results suggest that populations of P. m. victoriae sampled from habitats with diverse oxygen regimes differ in their physiological and biochemical responses to hypoxia.

Acute hypoxia-reperfusion triggers immunocompromise in Nile tilapia

Inadequate dissolved oxygen in the aquatic environment is a well-established cause of fish morbidity and mortality. The specific effects of hypoxia on immune function in fish, however, are not well characterized. In this study, the effects of acute hypoxia followed by reoxygenation (rapid tissue reperfusion) as a source of immunocompromise in Nile tilapia Oreochromis niloticus were investigated. Using a precision apparatus developed in our laboratory for hypoxia exposures, a series of assays of increasing specificity for immune function were performed on acutely hypoxia-stressed Nile tilapia: tier I consisted of histopathology, tier II of hematology, plasma chemistry, and determining cortisol concentration, and tier III of determining the phagocytic index and analyzing the expression of the cytokines transforming growth factor-beta (TGF-beta) and interleukin-1beta (IL-1beta). Nile tilapia were exposed to 7% oxygen saturation for 96 h, then tank water was rapidly reoxygenated. Sampling intervals were 48 and 96 h during hypoxia and 12 and 84 h during reperfusion. Histopathology showed no remarkable microscopic abnormalities in lymphoid or other tissues. Lymphopenia and neutrophilia were observed in peripheral blood. Plasma total protein, partial pressure of oxygen, and oxygen saturation were decreased in response to hypoxia. Plasma lipase decreased in response to hypoxia but returned to normal during reperfusion. Phagocytic capability and the phagocytic index decreased during hypoxia and 12 h reperfusion, whereas these values were recovered by 84 h reperfusion. The TGF-beta transcription continued to increase during the exposures, the greatest production being at 12 h reperfusion, whereas IL-1beta transcription decreased in response to hypoxia and reperfusion. We conclude that acute hypoxia triggered an overall downregulation of the immune system in the test fish. This suggests a possible factor in the pathogenesis of disease outbreaks in fish in which repeated, sublethal bouts of environmentally induced hypoxia lead to increased disease susceptibility and individual mortalities rather than massive fish kills.

Oxygen-dependent gene expression in fishes

The role of oxygen in regulating patterns of gene expression in mammalian development, physiology, and pathology has received increasing attention, especially after the discovery of the hypoxia-inducible factor (HIF), a transcription factor that has been likened to a "master switch" in the transcriptional response of mammalian cells and tissues to low oxygen. At present, considerably less is known about the molecular responses of nonmammalian vertebrates and invertebrates to hypoxic exposure. Because many animals live in aquatic habitats that are variable in oxygen tension, it is relevant to study oxygen-dependent gene expression in these animals. The purpose of this review is to discuss hypoxia-induced gene expression in fishes from an evolutionary and ecological context. Recent studies have described homologs of HIF in fish and have begun to evaluate their function. A number of physiological processes are known to be altered by hypoxic exposure of fish, although the evidence linking them to HIF is less well developed. The diversity of fish presents many opportunities to evaluate if inter- and intraspecific variation in HIF structure and function correlate with hypoxia tolerance. Furthermore, as an aquatic group, fish offer the opportunity to examine the interactions between hypoxia and other stressors, including pollutants, common in aquatic environments. It is possible, if not likely, that results obtained by studying the molecular responses of fish to hypoxia will find parallels in the oxygen-dependent responses of mammals, including humans. Moreover, novel responses to hypoxia could be discovered through studies of this diverse and species-rich group.

Hematology and clinical chemistry of cyprinid fish. Common carp and goldfish

Evaluation of the clinical status in aquatic species is compromised by the limited diagnostic techniques that can be performed in these species. The hematologic and plasma chemistry parameters can provide predictive information, although these parameters can be highly variable owing to the influence of various intrinsic and extrinsic factors. However, these parameters are fairly stable in acclimated, well-managed fish if stress is reduced during collection and samples are properly collected and analyzed. Evaluation of any single parameter is not predictive and, therefore, not recommended. Ideally, the diagnostic protocol should include evaluation of the hematologic indices, total and differential cell counts, TPP, glucose, sodium, and chloride. The practitioner who is routinely involved in aquatic animal medicine should consider in-house evaluation of these parameters.

Catecholamine-induced changes in oxygen affinity of carp and trout blood

Carp and trout blood maintained at low constant oxygen and carbon dioxide tensions was beta-stimulated. This activated the Na+/H(+)-exchanger of the red cell membrane, leading to increases in red cell pH (pHi) and cell water content, the latter resulting in dilution of hemoglobin and organic phosphates. The increase in pHi was rapid and maintained throughout the experimental period, the trout red cells showing the largest increase. Likewise swelling of the red cells was larger in trout than in carp blood. As a consequence of beta-stimulation the oxygen affinity of the blood increased. In trout the intracellular Bohr factor of unstimulated blood combined with the pHi increase upon stimulation could account for 85% of the increase in oxygen affinity, whereas it only covered 65% of the increase in carp blood. We therefore conclude that blood oxygen affinity is dependent on the red cell hemoglobin concentration in both species, the effect being more marked in carp.

Control and consequences of adrenergic activation of red blood cell Na+/H+ exchange on blood oxygen and carbon dioxide transport in fish

The catecholamines, adrenaline and noradrenaline, are released into the circulation of fish during a variety of physical and environmental disturbances that share the common feature of a requirement for enhanced blood oxygen transport. Indeed, the dominant factor controlling the mobilization of catecholamines from chromaffin tissue is a depression of blood oxygen content usually coinciding with a reduction of hemoglobin-O2 (Hb-O2) binding to 50-60% saturation. The elevation of plasma catecholamine levels, under such conditions, activates a beta-adrenergic cyclic AMP-dependent Na+/H+ exchanger on the red blood cell (rbc) membrane. The adrenergic responsiveness AMP-dependent Na+/H+ exchanger on the red blood cell (rbc) membrane. The adrenergic responsiveness of the rbc Na+/H+ exchanger to catecholamines varies both within and between species. Such inter- and intra-specific differences may reflect, in part, the availability of cell surface beta-adrenoceptors that are functionally coupled to adenylate cyclase. The activation of rbc Na+/H+ exchange and the accompanying profound adjustments of intracellular and extracellular acid-base status, nucleoside triphosphate (NTP) levels, and cooperativity of Hb-O2 binding have important consequences on both O2 and CO2 transfer and transport in the blood that vary markedly at the sites of oxygenation (the gill) and deoxygenation (the tissues) thereby enabling simultaneous amelioration of O2 loading and unloading. At the gill, oxygen transfer is enhanced owing to increases in Hb-O2 affinity and capacity while at the tissues, oxygen delivery is facilitated by a reduction of Hb-O2 affinity. This reduction in affinity at the tissues is a consequence of the combined effects of increased cooperativity of Hb-O2 binding and a rise in venous PCO2 (PvCO2) caused by the titration of HCO3- by H+ extruded by the rbc Na+/H+ exchanger. This elevation of PvCO2 may contribute to the rise in arterial PCO2 (PaCO2) observed after adrenergic activation of rbc Na+/H+ exchange that is caused primarily by impairment of rbc CO2 excretion related to modification of the intracellular acid-base status.

Ventilation, cardiac output and blood respiratory parameters in the carp, Cyprinus carpio, during hyperoxia

The specific ventilatory flow rate (Vw), cardiac output (Vb) and blood respiratory parameters were determined in the carp (Cyprinus carpio) during hyperoxia. Vb changed little during moderate hyperoxia (240-330 Torr) but slightly increased during extreme hyperoxia (430-490 Torr) while Vw decreased. This means that the ventilation-perfusion ratio considerably decreased during hyperoxia. The CO2 tension (PCO2) of blood rose, causing a corresponding decrease in blood pH. The O2 tensions (PO2) of arterial and mixed venous blood increased but remained low (about 40 Torr and 15 Torr, respectively). Consequently, the hemoglobin in the arterial and mixed venous blood was not saturated with O2 (about 80 and 55%, respectively) even during extreme hyperoxia. This indicates that most of the O2 which is consumed by the fish remains transported in a combined form during hyperoxia. During hyperoxia, when the decreased Vw was artificially elevated to the normoxic level, the PO2 of arterial blood (PaO2) rose further and the PCO2 and pH of arterial blood became restored to the normoxic levels. This suggests that the CO2 retention and the depressed increase in PaO2 during hyperoxia are mainly due to the decrease in Vw in the carp.

Adaptive respiratory responses of trout to acute hypoxia. II. Blood oxygen carrying properties during hypoxia

The effects of deep and acute hypoxia (PwO2 = 25 Torr) on oxygen transport characteristics (Hill number (n) and P50) were investigated in trout at 15 degrees C. When a fish is submitted to such an acute and deep hypoxia, a metabolic acidosis develops as soon as the arterial oxygen tension drops to about 15 Torr. We first showed that the hemoglobin of blood sampled at the end of the acidification period has an increased oxygen affinity. This improved affinity could be explained by the internal alkalisation of erythrocytes due to the extrusion of protons via a beta-adrenergic stimulation of Na+/H+ exchanges occurring at the onset of hypoxia and responsible for extracellular acidosis. Secondly we observed a significant increase (about 20%) of the number of blood cells per volume of blood during the acidosis. This cell number stays constant afterwards. The dual effects of a higher hemoglobin oxygen affinity and a greater amount of available hemoglobin improving blood oxygen loading at the fish gills appear to be a fast adaptive response to acute hypoxia. Surprisingly, we found that the elevated affinity occurring during acidosis remained constant as long as the fish were maintained in hypoxia, in spite of possible large variations of extracellular pH (pHe). This result is difficult to reconcile with the idea that the increase in affinity is imposed by intracellular pH (pHi), since in red blood cells pHi depends on pHe, thus any modification of pHe would in this case modify oxygen affinity.

Effects of nitrite exposure on blood respiratory properties, acid-base and electrolyte regulation in the carp (Cyprinus carpio)

Adult carp were subjected to 1 mM environmental nitrite for 48 h and nitrite uptake and changes in blood respiratory properties, extracellular electrolyte composition and acid-base status were examined. A constant influx of nitrite caused an accumulation of NO2- in plasma to 5.4 mM in 48 h. The fraction of methaemoglobin rose with plasma [NO2-] to 83%, and the arterial oxygen content decreased to extremely low values. Arterial PO2 increased as a compensation to this O2-shortage, whereas the O2 saturation of the functional (unoxidized) haemoglobin decreased, revealing a reduction in its O2 affinity. Blood haematocrit decreased as a result of red cell shrinkage, which caused very high red cell haemoglobin (Hb) concentrations. The erythrocytic nucleoside triphosphate (NTP) concentration showed a parallel increase whereby NTP/Hb, as well as the relative contributions of ATP and GTP to NTP, remained unchanged. Plasma [Cl-] declined by 15 mM in 48 h, offsetting the plasma [NO2-] increase, minor changes in plasma [HCO3-] and a considerable increase in plasma [lactate]. Arterial pH and [HCO3-] rose slightly during the first 24 h of nitrite exposure, but returned to control values at 48 h. The rise in plasma [lactate] was not reflected in an extracellular metabolic acidosis. Plasma [K+] increased by 94% in 48 h, revealing an uncompensated extracellular hyperkalemia, whereas plasma [Na+] decreased, and plasma [Ca++] was unchanged. Plasma osmolality remained essentially constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute exposure of rainbow trout to mild and deep hypoxia: O2 affinity and O2 capacitance of arterial blood

Respiratory properties and pH of blood were followed during acute exposure of rainbow trout to three levels of environmental hypoxia at 15 degrees C. In a first stage, the blood oxygen affinity was preserved (mild hypoxia, PwO2 = 60 mm Hg) or slightly increased (deep hypoxia, PwO2 = 35 mm Hg), despite a simultaneous drop in arterial pH within the first 5-10 min. This is possibly caused by a catecholamine induced increase in red cell pH. The second stage showed for the mild hypoxia group a temporary increase in affinity followed by a recovery within 60 min, correlating with the changes in arterial pH. The deep hypoxia group, however, further increased the blood oxygen affinity, due to a rapid decrease in the ATP:Hb4 and GTP:Hb4 molar ratios within the following 1-2 h. This was associated with a complete pH recovery. Very deep hypoxia (PwO2 = 30 mm Hg) furthermore elicited a 20% increase in blood hemoglobin concentration within 20 min. This group showed a more pronounced drop in blood pH, without a complete recovery. Calculated values of the arterial blood oxygen capacitance, beta bO2, are discussed in the context of the very different responses of trouts acutely subjected to mild and deep hypoxia, respectively.

Changes in blood metabolites following stress from capture and handling of the marine teleost Girella tricuspidata

Whole blood nucleoside triphosphate (NTP) and lactate in the parore (Girella tricuspidata, Fam: Kyphosidae) were monitored over a period of 12 hr following capture by gill net. An increase in NTP during the post-capture recovery period was mainly attributable to a significant rise (P less than 0.05) in the NTP component guanosine triphosphate (GTP). The rise in GTP levels correlated with the decline in blood lactate (r = -0.72) accumulated during the period of capture stress. It is suggested that metabolism of lactate via the Krebs cycle may be responsible for the rise in GTP.

Effect of acclimation temperature on intraerythrocytic acid-base balance and nucleoside triphosphates in the carp, Cyprinus carpio

In carp acclimated to 20 degrees C or 10 degrees C intraerythrocytic pH (pHi) and plasma pH (pHe) were determined in vitro after equilibration with CO2 in either O2 or N2. ATP and GTP were determined with an enzymatic assay described in detail. The relationship between pHi, pHe and oxygen saturation was not affected by the acclimation temperature and was (pHi-6.10) = (0.853-0.159 X S) X (pHe-6.21) There was a slight but significant decrease in ATP at 20 degrees C. Apparent buffer values were affected by oxygenation and temperature. It is concluded from the recalculated CO2 Bohr factor and from the temperature effect on the buffer value that carp hemoglobin forms carbamate which decreases at a higher temperature. These changes in ATP and carbamate can partly account for the increase in whole blood oxygen affinity in carp acclimated at a high temperature.

Effect of acclimation temperature on oxygen transport in the blood of the carp, Cyprinus carpio

The temperature dependence of the O2 equilibrium in whole blood was measured in carp acclimated for more than 3 weeks at 10 degrees C or 20 degrees C water temperature. O2 combining curves were obtained for the same samples at 10 degrees C or 20 degrees C using blood from the 10 degrees C or 20 degrees C acclimated fish (group A) or only at the acclimation temperature (group B). Whereas in group B the P50 was about the same at both temperatures, in group A P50 was higher at 20 degrees C than at 10 degrees C, yielding an apparent heat of oxygenation delta H = -9.9 kcal/mol at pH = 8.0. The CO2 Bohr effect in group A was delta log P50/delta pH = -0.93 at 20 degrees C and -1.17 at 10 degrees C, whereas in group B no temperature effect was seen (-0.98 and -0.97). The acclimation temperature had no effect on the electrophoretic Hb pattern. As expected, the in vivo pH changed inversely with temperature from 8.06 at 10 degrees C to 7.73 at 20 degrees C, enhancing the temperature-induced shift in P50. Acclimation reverses partly the changes in O2 affinity, thereby improving the uptake of oxygen in the gills.

Effects of exercise stress on acid-base balance and respiratory function in blood of the teleost Tinca tinca

We measured the effects of severe, short-term exercise stress on the acid-base balance, the O2 transporting properties and the cofactors for O2 binding in the blood of tench, Tinca tinca. Short-term severe exercise resulted in a drastic decrease in arterial blood pH which is attributed to a mixed respiratory and metabolic acidosis. Concomitantly arterial PO2 rose in apparent compensation for the detrimental effects of the acidosis on O2 transport by the blood.

Blood oxygen transport of hypoxic Salmo gairdneri

The in vivo blood oxygen binding properties of rainbow trout were studied in normoxia and hypoxia (PO2 55-60 mmHg). Owing to hypoxia the in vivo oxygen dissociation curve of blood was shifted to the left; the P50 value decreased from 37 mmHg in normoxia to 27 mmHg in hypoxia. Hypoxia also caused an increase in the erythrocytic volume, a decrease in the concentrations of ATP and hemoglobin inside the cell, and an increase in the intraerythrocytic pH. All these responses are interrelated. The swelling of the erythrocytes decreased the concentrations of ATP and Hb in the cell. This decrease changed the Donnan distribution of protons across the red cell membrane, thus increasing the intraerythrocytic pH. The increase in the intraerythrocytic pH was the main cause of the increase in the blood oxygen affinity. Owing to the increased blood oxygen affinity the oxygen transport from gills to tissues in hypoxia was only slightly decreased from that in normoxia. However, as the venous oxygen tension decreased in hypoxia, the diffusion of oxygen from tissue capillaries to the cells was probably slowed down in hypoxia when compared to normoxia.

Oxygen transport and acid-base balance in the blood of the sheatfish, Silurus glanis

Oxygen binding and buffer properties of the blood of the sheatfish, Silurus glanis, were investigated in vitro at 20 and 10 degrees C. The O2 binding curves were hyperbolic with P50 = 10.1 mm Hg (20 degrees C, pH = 7.5) and 4.6 (10 degrees C, pH = 7.5). There was a very large Bohr effect with an average delta log P 50/delta pH of - 1.14. At 20 degrees C this value tended to be higher than at 10 degrees C. As a consequence the apparent heat of oxygenation depended on pH. The mean value of delta H was -10.4 kcal/mol. The Haldane effect was pronounced too (delta pH/delta S = -0.14) as was the Root effect. Isoelectric focussing revealed 3 major hemoglobin fractions with isoionic points in a more alkaline region than in carp hemoglobin. The non-bicarbonate buffer value was -10 mmol . 1-1. pH -1. The intraerythrocytic pH depended on the extracellular pH and the O2 saturation: pH = (0.87 - 0.14 S) (pHe -6.68 + 6.48). Delta pH/delta t for a constant CO2 content was -0.0166.