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  • 1
    Electronic Resource
    Electronic Resource
    Divalent cations enhance ammonia excretion in Lahontan cutthroat trout in highly alkaline water (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 50 (1997), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The Lahontan cutthroat trout lives under highly alkaline and saline conditions in Pyramid Lake, Nevada (pH 9.4; 0.2 mmol 1−1 Ca++; 7.3 mmol 1−1 Mg++). These experiments were conducted to study the possible roles of water Ca++ and Mg++ concentrations on ammonia excretion in the Lahontan cutthroat trout under highly alkaline conditions. The basic protocol of the experiments was to determine ammonia excretion rates during the following three exposure periods (each of 3-h duration) in sequence: (a) in normal lake water; (b) in soft lake water with the divalent cation concentrations reduced; and (c) in the soft lake water with either Ca++ or Mg++ (or no divalent cations added) added back at the appropriate lake water concentration. The soft-water exposure caused a significant reduction in ammonia excretion to about half of the control (original lake water) levels. When either Ca++ or Mg++ was added to the soft water in the third exposure period, the ammonia excretion rates were increased more than twofold back to lake water levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1997.tb01630.x
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  • 2
    Electronic Resource
    Electronic Resource
    Responses of juvenile rainbow trout, under food limitation, to chronic low pH and elevated summer temperatures, alone and in combination (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 52 (1998), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Rainbow trout were exposed (90 days) in synthetic soft water to sublethal low pH (5.2) and a simulated climate warming scenario (+2°C above the control summer temperature range of 16.5–21° C), alone and in combination, under conditions of limited food (∼4% dry body weight day−1). Weight specific oxygen consumption rates (Mo2) were ∼55% of Mo2(max), in contrast to ∼75% of Mo2(max) found in trout fed an unlimited ration. This is likely due to a reduction in food quantity and thus feeding activity. However, the trout exposed to low pH at control temperatures exhibited higher conversion efficiencies and increased growth. In contrast, trout exposed to +2°C had reduced growth rates. No ionoregulatory disturbance occurred in any treatment, suggesting that this ration was sufficient to provide a replacement salt load in the diet. Energy budgets indicated that the limited ration resulted in a lowered optimum temperature for growth, with a greater proportion of the energy intake dissipated for metabolic expenditure, resulting in reduced conversion efficiencies. A fourfold reduction in faecal and unaccounted energy losses indicated higher absorption efficiencies than in satiation-fed trout.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1998.tb01553.x
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  • 3
    Electronic Resource
    Electronic Resource
    Calcium regulation in the freshwater-adapted mummichog (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 51 (1997), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In light of recent findings of an unusual pattern of ionoregulation (high Na+ uptake and negligible Cl- uptake) in the freshwater-adapted mummichog Fundulus heteroclitus, the pattern of Ca2+ regulation was examined. Under control conditions (water Ca2+= 200μEq l-1), unidirectional Ca2+ influx was 11 ± 4 nEq g-1 h-1. Acute variation of external Ca2+ levels revealed a saturable Ca2+ uptake system with a relatively high affinity (Km= 125 ± 36 μEq 1-1) and a transport capacity (Jmax= 31 ± 4 nEq g-1 h-1) comparable to those of other teleosts. Lanthanum (equimolar to [Ca2+]) significantly blocked Ca2+ uptake by 67% whereas magnesium had no effect. Chronic low Ca2+ exposure (50 μEq 1-1) stimulated Ca2+ uptake almost three-fold above control values, whereas chronic high Ca2+ exposure (20000 μEq 1-1) had no effect. Lanthanum and chronic low Ca2+ treatments disturbed the normally positive Ca2+ and Na+ balances of the animals whereas acid-base balance and ammonia excretion were undisturbed. The results indicate that Ca2+ regulation by the mummichog conforms to the model for freshwater Ca2+ transport whereby chloride cells on the gills take up Ca2+ actively from the water. However, the absence of extra-intestinal Cl- uptake and the recent demonstration of significant Ca2+ uptake by opercular epithelia raise questions about the relative roles of branchial and opercular epithelial chloride cells in freshwater F. heteroclitus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1997.tb02519.x
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  • 4
    Electronic Resource
    Electronic Resource
    Zinc binding to the gills of rainbow trout: the effect of long-term exposure to sublethal zinc (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 52 (1998), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of sublethal waterborne Zn (2·28 μmol l−1) on Zn binding kinetics to the apical gill surface were studied in juvenile rainbow trout (Oncorhynchus mykiss). Two separate radiotracer techniques were employed to ascertain this information. First, in vitro binding kinetic experiments were performed at extremely elevated zinc concentrations (up to 20 mmol l−1) to measure relatively low-affinity binding sites at the gill epithelium. There were no differences in Zn binding parameters (Km and Bmax) for fish sublethally exposed to Zn for 21 days and their simultaneous controls. Nevertheless, Ca did have an increased inhibitory effect on Zn binding in Zn-exposed fish suggesting that the anionic groups on the gill epithelium of these fish had been altered in some manner. Additionally, in vivo Zn binding kinetics were investigated using environmentally relevant waterborne Zn concentrations (low μmol l−1 range) to isolate high-affinity Zn binding sites (Ca transporters). No appreciable alterations in the Km and Bmax values for Zn binding were seen between the Zn-exposed group and its simultaneous control following 15 days of exposure. Furthermore, no significant differences in CC morphometry were observed between treatments. Despite these lack of treatment effects, there were temporal alterations in Km, Bmax and CC fractional surface area in both groups. It is proposed that these fluctuations are controlled by hormonal factors (such as stanniocalcin), believed to play a role in Ca influx.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1998.tb00957.x
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  • 5
    Electronic Resource
    Electronic Resource
    Red blood cell adrenergic responses in Amazonian teleosts (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 52 (1998), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Erythrocytes from Amazonian teleosts of the Rio Negro were surveyed for the presence of adrenergically mediated Na+/H+ exchange. Washed red blood cells (RBCs) incubated in HEPES-buffered Cortland saline were stimulated with 10−4 M L-adrenaline. The adrenergic response was clearly present in two characids, the tambaqui Colossoma macropomom and the jaraqui Semaprochilodus insignis, as demonstrated by a decrease in the pHc-pHi gradient across the RBC membrane, an uptake of Na+ from the extracellular medium, and RBC swelling. The latter was signalled by increased mean corpuscular volume (MCV) and decreased mean corpuscular haemoglobin concentration (MCHC). The response did not occur in two other characids, the black piranha Serrasalmus rhombeus and the aracu Leporinus fasciatus or in two silurid catfish, the piranambu Pinirampus pirinampu and the acari-bodo, armoured catfish, Pterygoplichthys multiradiatus. In acari-bodo, the Na+/H+ exchange response was similarly lacking under anoxic conditions. Oxygenated/deoxygenated comparisons revealed the presence of a marked Root effect in jaraqui and its absence in acari-bodo. GTP dominated over ATP as the major intracellular phosphate in all six species. There were no significant changes in any nucleoside phosphate (ATP, ADP, AMP, GTP, GDP, or GMP) in response to adrenaline in any species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1998.tb01554.x
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  • 6
    Electronic Resource
    Electronic Resource
    On the Energy of a Unit Vector Field (1997)
    Springer
    Geometriae dedicata 64 (1997), S. 319-330 
    Details
    ISSN: 1572-9168
    Keywords: Riemann manifolds ; unit vector field ; sasaki metric ; Hopf vector fields.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The energy of a unit vector field on a Riemannian manifold M is defined to be the energy of the mapping M → T 1 M, where the unit tangent bundle T 1 M is equipped with the restriction of the Sasaki metric. The constrained variational problem is studied, where variations are confined to unit vector fields, and the first and second variational formulas are derived. The Hopf vector fields on odd-dimensional spheres are shown to be critical points, which are unstable for M=S 5,S 7,..., and an estimate on the index is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1017976425512
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  • 7
    Electronic Resource
    Electronic Resource
    A comparative allometric study of the morphometry of the gills of an alkalinity adapted cichlid fish,Oreochromis alcalicus grahami, of Lake Magadi, Kenya (1996)
    Springer
    International journal of salt lake research 5 (1996), S. 131-156 
    Details
    ISSN: 1573-8590
    Keywords: Lake Magadi ; lagoons ; tilapia ; alkalinity ; gills ; diffusion ; respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geography
    Notes: Abstract A morphometric analysis of the gills ofOreochromis alcalicus grahami has been carried out on specimens from ecologically distinct lagoons and a water-holding tank of Lake Magadi, a highly alkaline salt lake situated in a volcanically active region of the southern part of the Great Rift Valley in Kenya. The data were compared with those fromOreochromis niloticus, a close relative that lives in fresh water and with data from other fresh water and marine fish. Our primary goal was to identify the possible adaptive features which enable the fish to survive in an environment characterized by severely fluctuating levels of oxygen, a condition exacerbated by factors such as high temperature, alkalinity and osmolarity. The specimens ofO. a. grahami from the south-western lagoons of the lake had gills better adapted for gas exchange with a body mass specific diffusing capacity for oxygen which was about 2 times greater than that of the gills of the specimens from the fish spring lagoons and 2.5 times that of those from the water-holding tanks. Some parameters of the gills ofO. a. grahami, e.g. the gill filament length and number of gill filaments are significantly greater than those ofO. niloticus but the number of secondary lamellae, area of secondary lamellae and the diffusing capacity of the gills are similar in the two species. Compared with most other fish, the gills ofO. a. grahami appear to be particularly well adapted for gas exchange especially by having a thin water-blood barrier. Perhaps in no other extant fish have the gills had to be so exquisitely designed to meet environmental extremes and regulate complex and at times conflicting functions such as gas exchange, iono-regulation, acid-base balance and nitrogenous waste excretion as inO. a. grahami
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01995827
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  • 8
    Electronic Resource
    Electronic Resource
    Ammonia and urea excretion in the tidepool sculpin (Oligocottus maculosus): sites of excretion, effects of reduced salinity and mechanisms of urea transport (1995)
    Springer
    Fish physiology and biochemistry 14 (1995), S. 111-123 
    Details
    ISSN: 1573-5168
    Keywords: nitrogenous waste products ; gills ; unidirectional urea flux ; marine teleost ; osmoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tidepool sculpins live in a variable environment where water temperature, salinity, gas tensions, and pH can change considerably with the daily tide cycle. Tidepool sculpins are primarily ammoniotelic, with 8–17% of nitrogen wastes excreted as urea. The majority of net ammonia (Jnet amm; 85%) and urea (Jnet urea; 74%) excretion occurred across the gill, with the remainder excreted across the skin, the kidney, and/or gut. Acute (2h) exposure to 50% seawater significantly increased Jnet urea (2.8-fold), but reduced Jnet amm (3.5-fold). In fish exposed to 50% seawater for 1 week, Jnet urea returned to control values, but Jnet amm remained slightly depressed. Unidirectional urea influx (Jin urea) and efflux (Jout urea) were measured using14C-urea to determine if urea was excreted across the gills by simple diffusion or by a carrier-mediated mechanism. Jin urea increased in a linear manner with increasing urea water levels (0–11 mmol N l−1), while Jout urea was independent of external urea concentrations. As well, Jnet urea and Jout inurea were not significantly different from one another, indicating the absence of “back transport”. Urea analogs and transport inhibitors added to the water did not have any consistent effect on unidirectional urea flux. These results demonstrate that ammonia and urea excretion rates and sites of excretion in tidepool sculpins are very similar to those found in other marine and freshwater teleosts. Urea and ammonia may play a role in osmoregulation as excretion rates and tissue levels were influenced by changes in water salinity. Finally, we found no evidence for a specific urea carrier; branchial urea excretion is likely dependent on simple diffusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00002455
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  • 9
    Electronic Resource
    Electronic Resource
    Respiratory gas exchange, nitrogenous waste excretion, and fuel usage during starvation in juvenile rainbow trout, Oncorhynchus mykiss (1996)
    Springer
    Journal of comparative physiology 165 (1996), S. 542-551 
    Details
    ISSN: 1432-136X
    Keywords: Starvation ; Respiratory quotient ; Nitrogen quotient ; Fuel ; Rainbow trout, Oncorhynchus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Oxygen consumption, CO2 excretion, and nitrogenous waste excretion (75% ammonia-N and 25% urea-N) were measured daily in 4-g rainbow trout over a 15-day starvation period. Oxygen consumption and CO2 excretion declined while N excretion increased transiently in the mid-part of the starvation period but was unchanged from control levels at the end. Component losses (as percentage of total fuel used) of protein, lipid, and carbohydrate were 66.5, 31.1, and 2.4% respectively, as measured from changes in body weight and body composition, the latter relative to a control group at day 0. Instantaneous fuel use, as calculated from the respiratory quotients and nitrogen quotients, indicated that relative protein use rose during starvation, but contributed at most 24% of the aerobic fuel (as carbon). Lipid metabolism fell from about 68 to 37%, and was largely replaced by carbohydrate metabolism which rose from 20 to 37%. We conclude that the two approaches measure different processes, and that the instantaneous method is preferred for physiological studies. The compositional method is influence by greater error, and measures the fuels depleted, not necessarily burned, because of possible interconversion and excretion of fuels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387515
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  • 10
    Electronic Resource
    Electronic Resource
    The effects of arginine vasotocin and catecholamines on nitrogen excretion and the cardio-respiratory physiology of the gulf toadfish, Opsanus beta (1998)
    Springer
    Journal of comparative physiology 168 (1998), S. 461-472 
    Details
    ISSN: 1432-136X
    Keywords: Key words Urea ; Ammonia ; Gill ; Arginine vasotocin ; Adrenaline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Simultaneous measurements of cardio-respiratory variables, oxygen uptake and whole body urea/ammonia/tritiated water effluxes were performed on cannulated gulf toadfish, Opsanus beta, before and after intra-arterial injection of the vasoactive agents, adrenaline, isoproterenol and arginine vasotocin. These experiments were conducted to test the hypothesis that the phenomenon of pulsatile urea excretion might reflect sudden changes in the general diffusive properties of the gill for solute transfer. Injection of isoproterenol (final nominal circulating level = 10−6 mol l−1), was used as a tool to maximise the diffusive and perfusive conditions for branchial solute transfer. This protocol caused a pronounced reduction in arterial blood pressure, an elevation of cardiac frequency and associated increases in whole body urea and tritiated water effluxes; ammonia excretion and oxygen uptake were unaffected. Injection of adrenaline (final nominal circulating level=10−6 mol l−1), caused a significant increase in arterial blood pressure and a tachycardia, yet nitrogen excretion and oxygen uptake were unaffected. Injection of arginine vasotocin, caused a dose-dependent (final nominal circulating levels = 10−11–10−9 mol l−1) increase in arterial blood pressure without affecting cardiac or ventilation frequency. At the two higher concentrations, arginine vasotocin caused large and transient increases in urea excretion without significantly affecting ammonia, water or oxygen fluxes. These results suggest that increased gill diffusive or perfusive conductance, while capable of augmenting urea efflux, cannot fully explain the sudden and massive increases in urea transfer associated with pulsatile urea excretion in toadfish. It is suggested that pulsatile urea excretion in this species may reflect a specific enhancement of urea excretion under the control of the neurohypophyseal hormone, arginine vasotocin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600050166
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