Cavefish cope with environmental hypoxia by developing more erythrocytes and overexpression of hypoxia-inducible genes

Dark caves lacking primary productivity can expose subterranean animals to hypoxia. We used the surface-dwelling (surface fish) and cave-dwelling (cavefish) morphs of Astyanax mexicanus as a model for understanding the mechanisms of hypoxia tolerance in the cave environment. Primitive hematopoiesis, which is restricted to the posterior lateral mesoderm in other teleosts, also occurs in the anterior lateral mesoderm in Astyanax, potentially pre-adapting surface fish for hypoxic cave colonization. Cavefish have enlarged both hematopoietic domains and develop more erythrocytes than surface fish, which are required for normal development in both morphs. Laboratory-induced hypoxia suppresses growth in surface fish but not in cavefish. Both morphs respond to hypoxia by overexpressing hypoxia-inducible factor 1 (hif1) pathway genes, and some hif1 genes are constitutively upregulated in normoxic cavefish to similar levels as in hypoxic surface fish. We conclude that cavefish cope with hypoxia by increasing erythrocyte development and constitutive hif1 gene overexpression.

Cardiorespiratory responses to haemolytic anaemia in rainbow trout Oncorhynchus mykiss

To quantify cardiorespiratory response to experimental anaemia in rainbow trout Oncorhynchus mykiss, a 24 h phenylhydrazine treatment was used to reduce haematocrit to almost one third of its initial value over 4-5 days. In response, relative blood velocity in the ventral aorta (an index of cardiac output) progressively increased to more than double to its normocythaemic value and there was no significant change in routine oxygen uptake. Thus, the primary compensatory response to anaemia was an increase in cardiac output.

Anaemia adjusts the aerobic physiology of snapper (Pagrus auratus) and modulates hypoxia avoidance behaviour during oxygen choice presentations

The effect of altered oxygen transport potential on behavioural responses to environmental hypoxia was tested experimentally in snapper, Pagrus auratus, treated with a haemolytic agent (phenylhydrazine) or a sham protocol. Standard metabolic rate was not different between anaemic and normocythaemic snapper (Hct=6.7 and 25.7 g dl(-1), respectively), whereas maximum metabolic rate, and hence aerobic scope (AS), was consistently reduced in anaemic groups at all levels of water P(O(2)) investigated (P<0.01). This reduction of AS conferred a higher critical oxygen limit (P(crit)) to anaemic fish (8.6±0.6 kPa) compared with normocythaemic fish (5.3±0.4 kPa), thus demonstrating reduced hypoxic tolerance in anaemic groups. In behavioural choice experiments, the critical avoidance P(O(2)) in anaemic fish was 6.6±2.5 kPa compared with 2.9±0.5 kPa for controls (P<0.01). Behavioural avoidance was not associated with modulation of swimming speed. Despite differences in physiological and behavioural parameters, both groups avoided low P(O(2)) just below their P(crit), indicating that avoidance was triggered consistently when AS limits were reached and anaerobic metabolism was unavoidable. This was confirmed by high levels of plasma lactate in both treatments at the point of avoidance. This is the first experimental demonstration of avoidance behaviour being modulated by internal physiological state. From an ecological perspective, fish with disturbed oxygen delivery potential arising from anaemia, pollution or stress are likely to avoid environmental hypoxia at a higher P(O(2)) than normal fish.

The interactive effects of hypoxemia, hyperoxia, and temperature on the gill morphology of goldfish (Carassius auratus)

Acclimation of crucian carp and goldfish to temperatures below 15°C causes covering of the gill lamellae by a mass of cells termed the interlamellar cell mass (ILCM). Here we explore the cues underlying gill remodeling (removal or growth of an ILCM) and specifically test the hypotheses that 1) depletion of internal O2 stores in the absence of any change in external O2 status can trigger the removal of the ILCM in goldfish acclimated to 7°C, 2) exposing fish acclimated to 25°C to an abundance of O2 (hyperoxia) can reverse the gill remodeling (i.e., cause the covering of lamellae by an expansion of the ILCM), and 3) neuroepithelial cells (NECs) are involved in signaling the shedding of the ILCM. Hypoxemia induced by phenylhydrazine (anemia) or 5% CO caused a decrease in the ILCM from 80% to 23% and 35%, respectively. Hyperoxia exposure at 25°C caused an increase to 67% of total ILCM and a smaller decrease in the size of the ILCM when fish were transferred from 7 to 25°C. Daily sodium cyanide injections were used to stimulate NECs; this treatment led to a significant decrease in the ILCM. Thus, the three major conclusions of this study are 1) that gill remodeling can occur during periods of internal hypoxemia, 2) that O2 supply and demand may be a significant driving force shaping gill remodeling in goldfish, and 3) the NECs may play a role in triggering the shedding of the ILCM during hypoxia.

Wintering strategies by mountain goats in interior mountains

As with many ungulates inhabiting areas with potentially deep snow, winter is an important season for mountain goats ( Oreamnos americanus (de Blainville, 1816)) and is characterized by restricted movements and high juvenile mortality. We examined winter habitat selection and wintering strategies by mountain goats in two adjacent areas of southeastern British Columbia characterized by deep, moist snow and by shallow, dry snow. Fifteen GPS collars were placed on mountain goats in each area over two winters. Winter-range size did not differ between areas and comprised, on average, 2.2%–7.4% of male home range and 8.0%–14.1% of female home range. Topographic variables dominated habitat model selection. At the broad scale, mountain goats in both areas selected winter ranges closer to escape terrain on warmer aspects that contained lesser amounts of mature dense forest. At the fine scale, mountain goats in both areas selected rugged habitat at upper mid-elevations and on warmer aspects. Alpine areas were avoided in the deep snow area and selected in the shallow snow area. No selection for mature forests was observed in either area. Mountain goats, therefore, appeared to utilize open, high-elevation habitats in shallow snow zones, but they did not seek reduced snow levels in mature forest stands in deep snow areas.

Influence of hypoxia and of hypoxemia on the development of cardiac activity in zebrafish larvae

Cardiac activity and anaerobic metabolism were analyzed in zebrafish larvae raised under normoxia (PO(2) = 20 kPa) and under chronic hypoxia (PO(2) = 10 kPa) at three different temperatures (25, 28, and 31 degrees C). Heart rate increased with development and with temperature. Under normoxia, cardiac output increased significantly at high temperature (31 degrees C), but not at 28 or at 25 degrees C. Under chronic hypoxia, however, heart rate as well as cardiac output increased at all temperatures in larvae at about hatching time or shortly thereafter. Cardiac activity of larvae raised for 2 wk after fertilization with a reduced hemoglobin oxygen-carrying capacity in their blood (hypoxemia; due to the presence of CO or of phenylhydrazine in the incubation water) was not different from control animals. Whole body lactate content of these animals did not increase. Thus there was no indication of a stimulated anaerobic energy metabolism. The increase in cardiac activity observed during hypoxia suggests that at about hatching time receptors are present that sense hypoxic conditions, and this information can be used to induce a stimulation of convective oxygen transport to compensate for a reduction in bulk oxygen diffusion in the face of a reduced oxygen gradient between environmental water and tissues. Under normoxia, however, the PO(2) gradient between environmental water and tissues and diffusional oxygen transport assure sufficient oxygen supply even if hemoglobin oxygen transport in the blood is severely impaired. Thus, under normoxic conditions and with a normal metabolic rate of the tissues, convective oxygen transport is not required until approximately 2 wk after fertilization.

Temporal Variation in Fitness Components and Population Dynamics of Large Herbivores

▪ Abstract  In large-herbivore populations, environmental variation and density dependence co-occur and have similar effects on various fitness components. Our review aims to quantify the temporal variability of fitness components and examine how that variability affects changes in population growth rates. Regardless of the source of variation, adult female survival shows little year-to-year variation [coefficient of variation (CV <10%)], fecundity of prime-aged females and yearling survival rates show moderate year-to-year variation (CV <20%), and juvenile survival and fecundity of young females show strong variation (CV >30%). Old females show senescence in both survival and reproduction. These patterns of variation are independent of differences in body mass, taxonomic group, and ecological conditions. Differences in levels of maternal care may fine-tune the temporal variation of early survival. The immature stage, despite a low relative impact on population growth rate compared with the adult stage, may be the critical component of population dynamics of large herbivores. Observed differences in temporal variation may be more important than estimated relative sensitivity or elasticity in determining the relative demographic impact of various fitness components.

Spectral imaging of red blood cells in experimental anemia of Cyprinus carpio

In the present work we have studied the effect of experimental anemia induced at both low and optimal temperatures on erythropoiesis in Cyprinus carpio. The results showed that hemoglobin concentration per cell was similar in both temperature conditions, however, red blood cell (RBC) concentration was higher at the optimal temperature. Induced anemia caused an abrupt decrease in RBC concentration, while the hemoglobin concentration per cell remained unchanged. Recovery, as shown by electron microscopy, was characterized by the release of differentiating young and intermediate cells to the peripheral blood. It was revealed that with the progression of differentiation the nucleus/cytoplasm ratio decreases, the chromatin condenses and the shape of the nucleus changes from round to elliptical. Spectral imaging revealed an increase in the optical density of chromatin with the maturation of the cells. The chromatin that was dispersed over the nuclear volume in the young cells becomes highly ordered in the mature cells. Spectral similarity mapping revealed the formation of a novel structure of high symmetry, representing chromatin rearrangement during the process of cellular differentiation.

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.

Disruption of hemoglobin oxygen transport does not impact oxygen-dependent physiological processes in developing embryos of zebra fish (Danio rerio)

Embryonic hemoglobin circulated by the developing heart in the early vertebrate embryo is widely assumed (without substantiation) to perform the same vital role of O2 carriage that it does in fetuses and adults. In order to challenge this assumption, we measured highly O2-dependent physiological variables like O2 consumption, cardiac performance, and initial swim bladder filling in the presence and absence of functional hemoglobin in the embryos and early larvae of the zebra fish, Danio ( = Brachydanio) rerio. Functional ablation of hemoglobin by carbon monoxide or phenylhydrazine did not reduce whole-animal O2 consumption, which was approximately 85 to 90 mumol.g-1.h-1. Similarly, no differences in heart variables like ventricular pressure development or heart rate, which increased from 135 to 175 bpm between stages 36h and 96h (indicating developmental stages 36 and 96 hours after fertilization, respectively), were observed in these experiments. Initial opening of the swim bladder was not influenced in the presence of CO-occupied hemoglobin but was significantly impaired when the embryonic hemoglobin was chemically modified by incubation with phenylhydrazine. That aerobic processes continue without hemoglobin O2 transport indicates the adequacy in the embryo of simple O2 diffusion alone even in developmental stages with extensive convective blood circulation generated by the heart.

The effects of experimental anaemia on CO2 excretionin vitro in rainbow trout,Oncorhynchus mykiss

The effects of severe experimental anaemia on red blood cell HCO3 (-) dehydrationin vitro were examined in rainbow trout,Oncorhynchus mykiss. After 5 days of anaemia (haematocrit=4.9±1.1%) induced by intraperitoneal injection of phenylhydrazine hydrochloride, fish displayed elevated arterial CO2 tensions (anaemic PaCO2=3.19±0.42 torrvs. control PaCO2=1.35±0.17 torr) and a significant acidosis (anaemic pHa=7.73±0.04vs. control pHa=7.99±0.04). However, after 15-20 days of anaemia (hct=6.6±0.8%) induced by blood withdrawal, the arterial CO2 tension was significantly lower than the control value, suggesting that physiological adjustments occurred within this time period to compensate for the lowered haematocrit. Compensation probably did not involve alterations in ventilation, which was unaffected by 5 days of anaemia (anaemic[Formula: see text];w=786±187 ml min(-1) kg(-1) vs. control[Formula: see text];w=945±175 min(-1) kg(-1)), based on indirect Fick principle measurements.Potential adaptations to longer term anaemia at the level of the red blood cells were investigated using a radioisotopic HCO3 (-) dehydration assay. Owing to the difference in haematocrits, the HCO3 (-) dehydration rate for blood from anaemic fish was significantly lower than that for control fish following equilibration at the same CO2 tension. This difference was eliminated when HCO3 (-) dehydration rates were measured on blood samples adjusted to the same haematocrit, a result which implies that the intrinsic rate of CO2 excretion at the level of the red blood cell was not 'up-regulated' during anaemia. The difference was also eliminated by equilibrating the blood samples with CO2 tensions appropriate for the group from which the sample was obtained,i.e., PCO2=1.4 torr for control samples and PCO2=3.2 torr for anaemic samples; each at the appropriate haematocrit. It is concluded that the elevated PaCO2 helps to reset CO2 excretion to the control level, but that some additional physiological adjustment occurs to lower the PaCO2 after 15-20 days of anaemia.

Erythrodynamics in fish: recovery of the goldfishCarassius auratusfrom acute anemia

Goldfish (Carassius auratus) were rendered anemic through immersion in phenylhydrazine∙HCl, a cohort of [3H]thymidine-labelled erythrocytes was established, and recovery followed over a 234-d period. Red blood cell (RBC), hemoglobin (Hb), and hematocrit (Hct) levels increased in biphasic fashion during recovery, rapid increases to plateau values being followed by more modest increases to levels equalling those observed prior to treatment. During the initial rapid phase of response, increased ventilatory and cardiovascular activities probably compensated for deficits in oxygen-carrying capacity but, by elevating blood O2tension, may have suppressed erythropoiesis. Continuing slow increases in RBC, Hb, and Hct may point to some as yet unidentified alternative mechanism for stimulating red cell formation. During maturation, mean erythrocytic volume decreased, while mean erythrocytic hemoglobin level increased. Cycles of division of circulating juvenile erythrocytes occurred at roughly 56-d intervals, but did not appear to play a major role in elevating blood O2-carrying capacity. Division and karyorrhexis or cell breakdown were loosely correlated. Under the conditions employed, red cell half-life was approximately 80 d.

Maturation of the goldfish (Carassius auratus) erythrocyte

1. Cohorts of [3H]thymidine-labelled erythrocytes were examined over a 42-day period in goldfish (Carassius auratus L.) recovering from phenylhydrazine HCl-induced anemia under normoxic conditions at 20 +/- 1 degree C and maintained with minimal disturbance on a high nutritional plane. 2. As judged by changes in primary and derived hematological variables, maturation required 16-20 days. 3. Similar estimates were obtained using cytomorphic variables obtained by image analysing methods. 4. These suggest that juvenile red cells in this species can be identified on the basis of the following characteristics: major axis less than 9.2 microM; one-sided surface area not greater than approximately 50 microns2; axis ratio greater than 0.774; form factor greater than 0.938. 5. Corresponding values for mature cells are: major axis greater than 11.2 microns; area greater than 68.5 microns2; axis ratio less than 0.716; form factor less than 0.912. 6. These criteria, with values for dividing and karyorrhectic cell numbers, offer a basis for more detailed and dynamic characterization of the erythron during response to environmental variation than has previously been possible.