Hypoxic Fish Research Articles

Desensitization of Adrenaline-Induced Red Blood Cell H+ Extrusion in Vitro After Chronic Exposure of Rainbow Trout to Moderate Environmental Hypoxia

ABSTRACT The sensitivity of red blood cell Na+/H+ exchange to exogenous adrenaline was assessed in vitro using blood withdrawn from catheterized rainbow trout (Oncorhynchus my kiss) maintained under normoxic conditions [water or after exposure to moderate hypoxia for 48 h, which chronically elevated plasma adrenaline, but not noradrenaline, levels. Peak changes in whole-blood extracellular pH over a 30 min period after adding 50–1000 nmol l−1 adrenaline were employed as an index of sensitivity; the blood was pre-equilibrated to simulate arterial blood gas tensions in severely hypoxic fish . Blood pooled from normoxic fish displayed a dose-dependent reduction in whole-blood pH after addition of adrenaline. Blood pooled from three separate groups of hypoxic fish, however, displayed diminished sensitivity to adrenaline, ranging from complete desensitization to a 60% reduction of the response. Subsequent experiments performed on blood from individual (i.e. not pooled) normoxic or hypoxic fish demonstrated an inverse correlation between the intensity of H+ extrusion (induced by exogenous adrenaline addition) and endogenous plasma adrenaline levels at the time of blood withdrawal. However, acute increases in plasma adrenaline levels in vitro did not affect the responsiveness of the red blood cell to subsequent adrenergic stimulation. The intensity of H+ extrusion was inversely related to the in vivo between 2.67 and 10.66 kPa, and directly related to the logarithm of the endogenous plasma adrenaline level. The results suggest that desensitization of Na+/H+ exchange in chronically hypoxic fish is related to persistent elevation of levels of this catecholamine. This desensitization can be reversed in vitro as a function of time, but only when blood is maintained under sufficiently aerobic conditions.

The Use of Alpha-Methyl-p-Tyroslne to Control Circulating Catecholamines in the Dogfish Scyliorhinus Canicula: the Effects on Gas Exchange in Normoxia and Hypoxia

ABSTRACT We assessed the effectiveness of alpha-methyl-p-tyrosine in inhibiting catecholamine synthesis in the dogfish and examined the effects of catecholamine depletion on the cardiovascular system in normoxia and in response to hypoxia. Although alpha-methyl-p-tyrosine (50 mg day−1 intraperitoneally for 5 days) substantially reduced the dogfish’s ability to increase the level of circulating catecholamines in response to hypoxia, it also substantially reduced normoxic oxygen consumption in the whole animal, an observation not previously reported. Metabolic studies on isolated dogfish hepatocytes indicate that this is a direct effect on oxidative metabolism at the cellular level rather than any effect on the oxygen delivery function of the fish’s cardiovascular system. Despite the effects of alpha-methyl tyrosine on normoxic oxygen consumption, the present results indicate that the lack of any large increase in the circulating levels of catecholamines in response to hypoxia in fish treated with alpha-methyl tyrosine does not compromise their gas exchange ability.

Hypoxic Responses in a Fish From a Stable Environment: Blood Oxygen Transport in the Antarctic Fish Pagothenia Borchgrevinki

ABSTRACT The effects of hypoxic exposure on whole-blood oxygen-affinity were examined in the antarctic fish Pagothenia borchgrevinki. Fish exposed to for 11–14 days at −1·5°C had a P50 value of 20·6 ± 4·8 mmHg (S.D., N =13) at pH8-16, compared with 31·1 ± 4·3mmHg (N = 10) at pH8-00 for normoxic fish. Exposure to low oxygen levels resulted in a significant (66 %) rise in haemoglobin concentration, and erythrocyte [ATP] decreased by approximately 27%. There was no evidence for erythrocyte swelling. An aberrant gill morphology was observed in six fish and these showed unexpectedly high erythrocyte ATP levels. Oxygen-carrying capacity increased by approximately 40% in hypoxic fish and was correlated with a 34 % decrease in spleen mass. Despite the fact that antarctic fish have exceptionally low demands for oxygen and are unlikely ever to encounter environmental hypoxia, this antarctic fish has the necessary machinery to respond to hypoxia in a way that is typical of teleosts that naturally inhabit oxylabile environments. The ability to make short-term adaptive changes in the O2 delivery system in response to hypoxic exposure may be typical for vertebrates in general, rather than a feature seen only in those organisms which encounter environmental hypoxia on a regular basis.

Pathology of lindane poisoning and of hypoxia in the brown trout, Salmo trutta L.

A comparative study of the signs of lindane poisoning and of hypoxia in trout, Salmo trutta L., showed that the symptoms of both causes of death are similar. The rapid fading of gill colour within 2 h of death is characteristic of both treatments and distinguishes these from other causes of death. Vascular congestion and cellular damage of the liver is common to both treatments. The causes of death may be distinguished by the behaviour of the fish before death and by study of their effects on the gills. Hypoxic fish showed increased ventilatory activity, but other activity decreased. Exposure to lethal levels of lindane caused hyperactivity, convulsions, ataxia and intermittent paralysis. Although gill damage in both cases was slight it was distinctive. Lindane caused disarray of the secondary lamellae, and exposure to low dissolved oxygen levels caused breaks in the lamellar epithelium. This was only clearly visible under electron microscopical examination.

Ultrastructure and metabolism of skeletal muscle fibres in the tench: effects of long-term acclimation to hypoxia.

Tench (Tinca tinca) were acclimated to either aerated (P O 2 17.6 KPa) or hypoxic (P O 2 1.5 KPa) water for 6 weeks. Acclimation to hypoxia resulted in a decrease in mitochondrial volume fraction in both slow (22.9 to 15.0 %) and fast glycolytic (4.5 to 1.8 %) myotomal muscles fibres (P<0.01). Intermyofibrillar mitochondrial populations (4.4 to 1.2% slow; 0.6 to 0.04% fast fibres) were affected to a greater extent than those in the subsarcolemmal zone (18.5 to 13.8% slow; 3.9 to 1.8% fast fibres). After acclimation to hypoxia, cytochrome-oxidase activities decreased by 31 and 33 % in slow and fast fibres, respectively, but were maintained in the liver. Fibre size remained unchanged and actively differentiating fibres were observed in muscles from both groups of fish. Hypoxia resulted in a significant increase in myofibrillar volume fraction in both slow (43.1 to 56.1 %) and fast glycolytic fibres (73.1 to 82.7%) (P<0.05). Glycogen concentrations (mg/100g tissue) for liver (6616) slow muscle (1892) and fast muscle (334) were similar for fish acclimated to aerated or hypoxic water. Acclimation to hypoxia increased carnitine palmitoyl transferase activity (μmoles substrate utilised g·dry wt-1 min-1) in slow (0.42 to 1.1), fast glycolytic muscle (<0.01 to 0.15) and liver (1.1 to 3.7) indicating an enhanced capacity for fatty acid oxidation. Phosphofructokinase activities of fast glycolytic fibres were similar in fish acclimated to either aerated or hypoxic water, consistent with an unaltered capacity for anaerobic glycogenolysis. Hexokinase activities (μmoles substate utilised, g·dry wt-1 min-1) decreased in fast fibres (1.2 to 0.4) but were maintained in the slow muslce (2.1 to 2.5) and liver (4.5 to 4.8) of hypoxic fish. The activities of phosphofructokinase in slow muscle and phosphofructokinase, pyruvate kinase and lactate dehydrogenase in liver were two times higher in fish acclimated to hypoxia. An enhanced capacity for glycolysis in these tissues may reflect a reduced threshold for anaerobic metabolism during activity and/or an adaptation for acute exposure to anoxia in fish acclimated to hypoxia.

Structural and circulatory responses to hypoxia in the secondary lamellae ofSalmo gairdneri gills at two temperatures

The first gill arch ofSalmo gairdneri was fixed from normoxic (O2 saturation of the water >90%) and hypoxic (O2 saturation 25–30% for 5 days) fish at 10 °C and 18 °C, and from fish after one-day recovery from hypoxia at 18 °C. The secondary lamellae of the gills were analysed with morphometric methods for structural, haemotological and circulatory changes. During hypoxia a marked vascular distension took place at both temperatures. At both temperatures the vascular distension coincided with a shortening of the diffusion distance (36% at 10 °C and 21% at 18 °C) and a swelling of the erythrocytes (60% at 10 °C and 42% at 18 °C). The effects of these changes on the oxygen uptake of the gills are discussed.

Respiratory patterns and antipredator responses in the central mudminnow, Umbra limi, a continuous, facultative, air-breathing fish

The central mudminnow. Umbra limi, is a continuous facultative air breather whose respiration is primarily aquatic in normoxic water and primarily aerial in hypoxic water. Under these conditions the frequency of respiration (air breaths; branchial breaths) by the primary mode increases with temperature. In hypoxic water, fish exposed to simulated predator disturbance breathed air in synchrony where a breath by one fish was immediately followed by breaths from one or more other fish. Undisturbed fish breathed air at random times with respect to other individuals. The level of dissolved O2 at which fish switch from primarily aquatic to primarily aerial respiration during progressive hypoxia was positively related to temperature. When fish were exposed to progressive hypoxia in groups (n = 10) the transition to air breathing in terms of dissolved O2 concentration was unaffected by acclimation to hypoxia and by simulated predator disturbance. When held alone (isolated) and disturbed, fish became very active and switched to aerial respiration at a higher level of dissolved O2 than either fish held alone and undisturbed or fish held in a group of 10. During progressive hypoxia without access to air, mudminnows maintained both a high level or activity and frequency of branchial breathing down to 15 Torr (1 Torr = 133.322 Pa). Acclimation to hypoxia did not greatly increase resistance to hypoxia in fish without access to air.

The Ventilation, Extraction and Uptake of Oxygen in Undisturbed Flounders, Platichthys Flesus: Responses to Hypoxia Acclimation

ABSTRACT Gill ventilation , extraction of O2 from the ventilatory current and O2-uptake were measured in three groups of undisturbed flounders naturally buried in sand. Two groups were acclimated to normoxic water . One was studied in normoxic water, the other during acute exposure to hypoxic water (P1, O2 = 30 mmHg). A third group was acclimated to and studied in hypoxic water. Gill ventilation was measured directly using an electromagnetic flowmeter. The flowprobe, fitted to a plastic funnel, was placed over the fish’s mouth without making physical contact with the fish. Exhaled water for calculation of O2-extraction was siphoned from another plastic funnel placed over the upper operculum of the flounder. Acute hypoxia exposure of normoxic fish caused nearly a doubling in ventilation volume. In flounders acclimated to chronic hypoxia and studied in hypoxic water the ventilation volume reached a value approximately 3-5 times that of normoxic fish. O2-extraction averaged 76% in normoxic flounders. During acute hypoxia the value declined to 52%, the same O2-extraction was obtained in the chronically hypoxic fish. for the normoxia acclimated fish in normoxic water was 0 · 45 ml O2 · kg −1 .min − 1 declining to 0-12ml O2.kg − 1.min − 1 during acute exposure to hypoxia. of hypoxia acclimated fish in hypoxic water was 0 · 24 ml O2. kg − 1. min − 1. When compared in hypoxic water, the hypoxia acclimated fish show an unchanged O2-extraction of 52% in spite of a nearly two-fold increase in ventilation relative to that of the normoxia acclimated fish. Possible causes for this may be a left shift of the O2-Hb dissociation curves and an increase in the transfer factor for O2 over the gills in the hypoxia acclimated fish.

Cardiovascular responses of the winter flounder Pseudopleuronectes americanus to hypoxia

1. 1. Winter flounder exposed to hypoxic conditions (3.57 mg O 2/l X̄) were compared with normoxic group (7.81 mg O 2/l X̄) at 10°C. 2. 2. The hypoxic fish compensated for a diminished arteriovenous O 2 difference by an increased cardiac output in maintaining respiratory homeostasis. 3. 3. This adaptive cardiovascular response pattern to hypoxia would maximize the oxygen tension gradient across the gill epithelia while buried in sea floor sediments.

Effects of ambient P o 2 on hemoglobin-oxygen affinity and red cell ATP concentrations in a benthic fish, pleuronectes platessa

Previous studies have demonstrated that acclimation of mammals and fish to hypoxic conditions elicits opposite responses in red cell organic phosphate levels (an increase and a decrease, respectively). This investigation focuses on the “reverse” response — when the benthic fish Pleuronectes platessa, which occurs locally under hypoxic conditions, is subjected to higher oxygen tensions. Compared to the hypoxic ( P o 2 = 30 mm Hg) situation the ATP:Hb ratio is increased (1.1 to 1.8) and oxygen affinity is decreased (i.e. P 50 changed from 18 to 30 mm, at pH 7.7 and 15 °C) by acclimation to P o 2 of 150 mm Hg. Under hyperoxic conditions ( P o 2 = 300 mm Hg) the ATP: hemoglobin ratio and blood P 50 showed a surprising decrease and returned to values comparable to those in hypoxic fish (to 1.3 and 18 mm Hg, respectively). When “stripped” of organic and inorganic ions hemoglobin solutions prepared from fish acclimated at 30 and at 150 mm Hg have the same P 50 and Bohr effect values, showing that the intra-erythrocytic factor rather than changes in the hemoglobin molecules, are involved. The pure hemoglobin shows high sensitivity to ATP at physiological concentrations. There is evidence that apart from the direct helcotropic effects, ATP decreases oxygen affinity in the red cells through modification of the Donnan distribution of protons across the red cell membrane. Fish acclimated to 30 and 150 mm Hg oxygen tensions showed the same oxygen consumption rates at the same oxygen tensions.

Positive Buoyancy and Air-Breathing: A New Piscine Gas Bladder Function

Dormitator latifrons is unique among known air-breathing fishes in that it emerges an external respiratory organ when in hypoxic water. The fish normally does so by using supports or generating positive buoyancy by inflation of the gas bladder. To inflate the gas bladder in hypoxic water fish must first emerge the external respiratory organ. The gas bladder is then inflated with oxygen and carbon dioxide. However, inflation of the gas bladder did not commonly occur in the laboratory unless fish were away from visual and auditory disturbances.

Respiratory Responses to Hypoxia in Fish

Hypoxia is discussed in the widest sense, i.e., as the conditions under which cells suffer a lack of oxygen. From a consideration of the transfer of oxygen from the water to the cellular sites as a series of resistances, it is suggested that hypoxia can result from an increase in resistance anywhere along the chain, and possible types of hypoxia in fish are defined from this point of view. More detailed discussion is given in relation to (1) interference with gas transfer at the gill surface; (2) reduction in the blood O2 carrying capacity; (3) modifications in the cardiac and ventilatory frequencies and in the coupling between these two rhythms, and (4) the time course of the hypoxic stimulus. It is concluded that most of the increase in knowledge of hypoxia during the past ten years can be fitted into known theoretical frameworks, but there is still a great need for measurements of oxygen tension at all levels in the respiratory chain; attention needs to be directed to both diurnal and seasonal variations and especially to long-term changes in those environmental conditions which tend to result in hypoxia.

Adaptation to hypoxia by increased HbO 2 affinity and decreased red cell ATP concentration.

THERE is a decrease in the O2 affinity of mammalian haemoglobin (Hb) as the levels of 2,3-DPG or ATP are increased, which is explained by an allosteric effect on the HbO2 binding1,2. Similar observations on amphibians3 and fish4, which have molar ratios of ATP to Hb similar to those of DPG to Hb in mammals, suggest that red cell organic phosphates modulate Hb function in all vertebrates. The adaptation of mammals to various hypoxic stresses involves reduced HbO2 affinity5–9, the attendant increase in O2 “unloading” capacity being mediated by an increase in the concentration of red cell 2,3-DPG. We have found the opposite response in hypoxic fish and suggest that an increased O2 affinity results in increased O2 transport for the fish.

Capillary dilatation in response to hypoxia in the brain of a gobiid fish

Typhlogobius californiensis, a small fish living in tide pools, was exposed to 24–36 hr of hypoxia and instantly fixed by deep freezing. In freeze dried brain sections of hypoxic fish the capillary diameter increased 1.6 times and the % capillary area 2.4 times compared to normoxic controls. Since the average distance between open capillaries stayed constant the diameter increase accounted for the increase of capillary area. The fishes heart rate slows to 20% during hypoxia and does not overshoot on return to normoxia. The opercular frequency drops to 45%. The capillary dilatation may be important in surviving hypoxia and is discussed as an additional element of the diving response.