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  • 1
    Electronic Resource
    Electronic Resource
    The energy of Hopf vector fields (2000)
    Springer
    Manuscripta mathematica 101 (2000), S. 71-88 
    Details
    ISSN: 1432-1785
    Keywords: Mathematics Subject Classification (1991):53C20 (53C15, 58E15, 58E20)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract: The 3-dimensional Hopf vector field is shown to be a stable harmonic section of the unit tangent bundle. In contrast, higher dimensional Hopf vector fields are unstable harmonic sections; indeed, there is a natural variation through smooth unit vector fields which is locally energy-decreasing, and whose asymptotic limit is a singular vector field of finite energy. This energy is explicitly calculated, and conjectured to be the infimum of the energy functional over all smooth unit vector fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002290050005
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of extremely alkaline water (pH 9·5) on rainbow trout gill function and morphology (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 45 (1994), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Rainbow trout that were held under control conditions, at pH8·0, in moderately hard Hamilton tap water, had Cl− and Na+ influx rates (JCLin and JNa, respectively) of 270 and 300 μmol kg−1 h−1, respectively. Exposure to pH 9·5 water led to an immediate 67% decline in JCLin and a 45% reduction in JNain at 0–1 h. Influx rates declined further and by 4–5 h the net decreases in both JCLin and JNain approximated 80%. By 24 h JCLin had recovered to rates not significantly different from those at pH 8·0; while JNain only partially recovered and remained about 50% lower than control measurements through 72 h. The complete recovery of JCLin and partial recovery of JNain may have been related to a fourfold greater branchial chloride cell (CC) fractional surface area observed in rainbow trout exposed to pH 9·5 for 72 h. Ammonia excretion (JAmm) was about 170 μmol N kg−1 h−1 at pH 8·0 but was initially reduced by 90% over the first hour of high pH exposure. JAmm rapidly recovered and by 24 h it had returned to pre-exposure levels. This recovery tended to parallel the partial recovery of JNain. However, subsequent addition of amiloride (10−4M) to the water at 75 h led to no change in JAmm, despite a 50% reduction in JNain. Thus, it does not appear that there is a linkage between Na+ influx and the recovery of ammonia excretion under highly alkaline conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1994.tb01288.x
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  • 3
    Electronic Resource
    Electronic Resource
    The influence of dietary and waterborne zinc on heat-stable metal ligands in rainbow trout, Salmo gairdneri Richardson: quantification by 109Cd radioassay and evaluation of the assay (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 35 (1989), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The 109Cd binding assay of Eaton & Toal was critically evaluated and then used to assess the induction of cytosolic metal-binding ligands in rainbow trout exposed to Zn in the diet and/or in the water for 16 weeks. With purified rabbit Cd-Zn metallothionein (MT), 109Cd binding and total Cd recovery in the assay were linear up to 5 μg of protein; gel chromatography revealed a single peak. With heat-denatured extracts of gill, liver and intestine from control and Cd- and Zn-injected trout, 109Cd binding was generally linear with sample size. Gel chromatography demonstrated that 109Cd was bound by a protein with the same apparent weight as MT (∼ 11000 daltons), but significant binding occurred also at three other regions [molecular weight (mol wt) 〉70 000, 30000 and 〈3000]. In the dietary/waterborne Zn exposure, induced 109Cd-binding activity occurred not in the MT peak but in the low mol wt peak (〈 3000). Activity in the gill rose in response to both dietary and waterborne Zn, but the liver did not respond. The maximum five-fold elevation in the gill was primarily a waterborne effect. In the intestine, the maximum rise was 25-fold due to both factors. The thresholds for induction were 〉 39 μg Zn| in water, and 〉 90 mg kg | in the diet, but only when waterborne Zn was also high. There was no correlation between 109Cd binding and acid soluble thiol levels, which tended to decline at higher Zn exposures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1989.tb03006.x
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of β-adrenergic blockade on the recovery process after strenuous exercise in the rainbow trout, Salmo gairdneri Richardson (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 32 (1988), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Trout fitted with arterial catheters were subjected to 6 min of strenuous exercise, injected with either saline (controls) or the β-adrenergic antagonist propranolol, and monitored over the following 8-h recovery period. Control responses were very similar to those previously reported, except for much higher resting and post-exercise plasma catecholamine levels, and less marked RBC pHi regulation, perhaps due to season (February–May). Trout subjected to prior β-blockade would not exercise. Trout β-blocked immediately after exercise showed a much higher incidence of mortality during the recovery period, but accompanying symptoms were similar to those previously documented in control trout dying after exercise. Specific effects of post-exercise β-blockade seen in both survivors and mortalities were a sustained elevation of arterial Pco2 and an inhibition of blood glucose elevation. There were negligible effects on RBC pHi and volume regulation, blood metabolic acid and lactate dynamics, or plasma ion changes. The results provide little support for the hypothesis that β-adrenergic actions of plasma catecholamines are intimately involved in post-exercise recovery, but must be considered in the context of the ‘winter’ trout, where β-responses may be diminished.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1988.tb05395.x
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of acid and acid/aluminum exposure on circulating plasma cortisol levels and other blood parameters in the rainbow trout, Salmo gairdneri (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 32 (1988), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Softwater (Ca2+=50, Na+= 50(μequiv. l−1) acclimated rainbow trout were fitted with chronic arterial catheters to allow for repetitive blood sampling. After 48 h recovery they were then exposed to either control (pH 6.5, Al = 0μg l−1), acid (pH 4.8, Al = 0μg l−1) or acid plus aluminum (pH 4.8, A1 = 112 μg l−1) conditions for 72 h. Parameters measured included blood glucose, lactate, haemoglobin, haematocrit and plasma Na+, Cl−, protein and cortisol.Exposure to pH 4′8 alone caused no mortality, a moderate ionoregulatory disturbance and a transient elevation in plasma cortisol. All other parameters were not significantly different from controls. Addition of aluminum to this exposure caused 100% mortality with a mean survival time of only 27.0 h. There was a marked decrease in plasma ions, hyperglycemia, lactate accumulation, haemoconcentration, red cell swelling, and a sharp rise in plasma cortisol becoming greatly increased as the fish neared death. The mechanism of toxicity of acute acid/aluminum exposure, the role for cortisol under such conditions, and the validity of cortisol and glucose as indicators of stress in fish are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1988.tb05335.x
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  • 6
    Electronic Resource
    Electronic Resource
    Genetic structure of Lake Magadi tilapia populations (2000)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 56 (2000), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The control region of the mitochondrial DNA haplotype frequencies were significantly different among the two separate lagoon populations of Oreochromis alcalicus grahami in Lake Magadi and of O. a. alcalicus from lake Natron, and DNA fingerprint similarity indices were significantly higher for intra-population comparisons of the two Magadi lagoon populations and the Lake Natron population than the inter-population similarity indices among these populations. A modified Fst measure indicated population sub-division and the phylogeographic partitioning of the VNTR fragments observed were unique to specific populations further indicating substantial genetic differentiation. The lagoon populations within Lake Magadi demonstrated the same degree of genetic differentiation as either of these populations did to the outgroup (the Lake Natron population). There appears to be limited gene flow between Lake Magadi tilapia populations and this population structure has important implications for protecting locally adapted populations within this unique ecosystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.2000.tb00757.x
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  • 7
    Electronic Resource
    Electronic Resource
    Mechanisms of aluminium extraction and accumulation at the gills of rainbow trout, Oncorhynchus mykiss (Walbaum), in acidic soft water (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 38 (1991), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Rainbow trout were fitted with latex masks for the measurement of ventilatory flow rate (V̇w) and with opercular catheters for sampling expired water from close to the branchial surface. Fish were exposed for 6 h to pH 5.1, 4.7 or 4.1 in the presence (138 μg l 1) or nominal absence (1 μg 1–1) of Al. Inspired and expired Al concentrations and water pH were measured via the opercular catheters. Gills were sampled for accumulated Al at the end of the experiments. V̇w increased during Al exposures at all three pHs. However, in the absence of Al, V̇w increased only at pH 4.1. Aluminium extraction from the water and Al accumulation on the gills were highest at inspired pH 5.1 and lowest at pH 4.1, and correlated well with expired pH, which was 0.2–0.7 pH units higher than inspired pH. Gill Al accumulations amounted to only about one-tenth of deposition calculated from Al extraction from the water and V̇w, and gill Al was tightly bound to the branchial surface.Calculations of Al solubility, oversaturation, and species composition were made using measured expired pH values, and were compared with Al extraction from the water and measured gill Al concentrations. In general, these analyses indicated that reduced Al solubility near the gills is a reasonable explanation of Al extraction from the water, and that Al(OH)2+ and Al(OH)3° are the Al species most likely to interact initially at the gills. It is suggested that mucus sloughing removes most precipitated Al, and that only the charged form persists, bound to structural elements on the gill surface. A model incorporating these results, and pH changes in the fish gill micro-environment in general, is presented to explain previously-reported ionoregulatory and respiratory effects of Al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1991.tb03619.x
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  • 8
    Electronic Resource
    Electronic Resource
    Nitrogen metabolism and excretion in Allenbatrachus grunniens(L): effects of variable salinity, confinement, high pH and ammonia loading (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    Journal of fish biology 65 (2004), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The nitrogen metabolism and excretion patterns of the grunting toadfish Allenbatrachus grunniens and the effects of salinity on these processes were examined. Individuals of A. grunniens were subjected to several experimental treatments, including variable salinity (2 to 30), high pH (8·5 compared to 7·0 for controls), high environmental ammonia (10 mM) and confinement to small water volumes, and measurements were made of activities of selected enzymes of nitrogen metabolism, ammonia and urea excretion rates, and tissue and plasma contents of ammonia, urea and amino acids. Activities of key ornithine-urea cycle enzymes were rather low (e.g. liver carbamoyl phosphate synthetase III activity was 0·001 μmols min−1 g−1), and A. grunniens consistently demonstrated a low capacity for urea excretion despite significant elevations of plasma and tissue ammonia contents by the high pH and high ammonia treatments. This species could thus be categorized as ammoniotelic. Total free amino acid contents in plasma and tissues were increased by the high pH and high ammonia treatments, but no patterns were discerned in individual amino acids that would indicate any preferential accumulation (e.g. alanine and glutamine) as has been noted previously in several semi-terrestrial fish species. Thus, it appeared that A. grunniens was not unusual in its patterns of nitrogen metabolism and excretion in comparison to other ‘typical’ teleosts. Furthermore, manipulation of salinity had no major effects on nitrogen excretion in either this species or in comparative studies with the ureotelic gulf toadfish Opsanus beta. The results are discussed in the context of the broader pattern of nitrogen metabolism and excretion in the Batrachoididae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0022-1112.2004.00538.x
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  • 9
    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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  • 10
    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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